Weak El Nino Tries to Take Hold
But Is Expected to Fade
Overview: La
Nina starting brewing in early March 2010 and continued strengthening
through the end of that year, wrapping into 2011 and remained a dominant factor through the winter on into the early Spring of 2012. But starting in January of 2012, a subtle but steady shift started taking.cgiace. A long awaited pulse of the Active Phase of the Madden Julian Oscillation (MJO) began, causing the Southern Oscillation Index (SOI) to start dropping. But rather than abating as is usual after 3 weeks, the Active Phase of the MJO continued lingering in some form for months. With trade winds suppressed, warm water started migrating east along the equator and a small warm pool started building off Ecuador in March, making a little headway, fading some, then regaining ground in fit's and starts. By April a modest reinforcing feedback loop became established. This resulted in a steadily increasing pool of warmer than normal surface water in the far East Pacific. By early July 2012 it looked as if a fully blown El Nino event was underway with the SOI dropping to it's lowest point since the El Nino of 09-10. But as quickly as it started, the trend began to moderate, with a modest Inactive Phase of the MJO taking root and no net additional warm water build-up occurring. The SOI started cyclically loosing ground, then trying to reclaim past negative territory, but never exceeding the negative peak set in July. Presently the SOI continues in neutral territory with the warm water pool off Ecuador slowly but steadily loosing coverage and depth.
The
2011-2012 Winter season experienced 3 significant class storms, well below average, but there was a series of solid utility class storms that developed in-sync with the falling SOI and Active MJO run in Jan-March 2012. This resulted in some better than hoped for swell events and a late season dump of snow in the Sierra that helps to minimize drought concerns for California. But none of these system had enough energy to reach well into the interior continental US, with drought conditions becoming established. As Spring settled in, high pressure dug in stronger than usual in the Northeast Pacific driving unusually strong north winds down the CA coast and easterly trades over the Hawaiian islands as is typical during La Nina years. This resulted in much local north windswell for California and east windswell for Hawaii. A byproduct of these increased trades was much upwelling of colder than normal water between California and Hawaii, that in-turn reinforced high pressure above it, generating a localized feedback loop. So though the equatorial Pacific was trying to usher in El Nino, the Northeast Pacific was firmly entrenched in the effects of La Nina. This pattern also lead to drought over the Midwest in Spring and Summer months. Even the Southern Hemispheric storm pattern was affected, with only 3 significant class storms occurring. And even as of this report, the blocking high pressure and cold upwhelling pattern is still in control relative to the Northeast Pacific. There are some signs of moderation, though nothing overwhelming. And statistically, with La Nina having run it's typical 2 year cycle, the odds now move more in favor of a normal to slightly enhanced weather regime.
It is with that backdrop that we
look to the coming Fall and Winter of 2012/2013 with normal to slightly enhanced expectations for surf for Hawaii, Canada and the
US West Coast. The
paragraphs below describe the state of various indicators used to
assess long-term global weather conditions (be it either El Nino or La
Nina), followed by a revised set of criteria for assessing it's impact
on surf generation potential for the future.
Each
section first provides a basic tutorial on the feature being analyzed (in italics),
and it's state during El Nino and La Nina years. It is followed by an
analysis of how that feature is currently behaving. After all
features are reviewed, an overall analysis is provided along with
additional notes and conclusions summarizing the expected outcome for
the future.
MJO: The
Madden Julian Oscillation (MJO) is a pattern of wind and weather
anomalies that run along and over the equator circumnavigating the
globe from west to east in
roughly 40-60 day cycles, roughly 20-30 days of
the Active Phase followed by 20-30 days of the Inactive Phase at any
one point on it's path. The cycles alternate continuously year after year and are
stronger
during the northern hemisphere Fall, Winter and Spring season and
lessen during the summer. The classic pulse of the Active
Phase of the MJO results in a slackening of trade winds and an increase
in rainfall over the area it is present. The Active Phase is directly
followed by the Inactive Phase which manifests itself though increased
trades winds and reduced rainfall. The Active Phase of the MJO has been
i.cgiicated in fueling the development of Northern Hemisphere storms
during winter months and tropical storms in the Fall over the
Pacific , while the Inactive Phase has been i.cgiicated in fueling the
formation of tropical storm in the Atlantic during summer months. When
the strength of Active Phases of
MJO dominate, El Nino indicators strengthen. When the Inactive
Phase dominate, La Nina moves to the forefront. That is not to say that
the MJO causes either El Nino or La Nina, only that it appear to
support the development of either extreme of the ENSO cycle. In other
words, when the balance of energy favors the Active Phase, the odds of
El Nino developing increases. When the balance
shifts towards the Inactive Phase, La Nina becomes more
likely. The
balance has clearly favored the Active Phase since January 2012 with no
serious Inactive Phases have been evidenced since then. Noteworthy Active Phases occurred in Jan-Feb, April, June and August, but after the June run that ended in early July, no further headway was being made in MJO's assault on the momentum established by 2 years of La Nina. As of right now we remain in a completely neutral state. So it's taken 8 months of domination by the Active Phase just to turn the pattern to neutral, but not enough to fully swing the atmosphere into an El Nino pattern. At least as of now the Active Phase is looking to remain slightly dominant, with no serious Inactive Phase events modeled. More details of the MJO as
it relates to the current forecast is presented below.
SOI: First
we look at the Southern Oscillation Index (SOI). This number compares
surface pressure over Darwin Australia with pressure over Tahiti. If
this value is negative for an extended period of time, that indicates
average surface pressure is lower over Tahiti and higher over Darwin,
symptomatic of El Nino (or over short durations, ~ 20 days, the Active
Phase of the MJO). Positive values over longer times indicates La Nina
(or the Inactive Phase of the MJO for shorter durations). The greater
the negative or positive value over time, the stronger the ENSO (El Nino Southern
Oscillation) configuration (be it El Nino or La Nina). During El Nino
episodes wind flows from generally high pressure over Darwin towards
generally lower pressure over Tahiti, which is a reverse of what a
normal state is. When it's positive, the reverse it true, with higher
pressure over Tahiti and lower pressure over Darwin, typical of La
Nina, with wind flowing east to west, typical of the trade wind pattern for this
region, only more so. The March-June time frame is called the 'Spring Unpredictability Barrier'. During this time wild swings in the SOI can occur, driven by pulses of the MJO. These swings do not always reflect the start of a long term trend, and often can be 'red-herrings' or 'false starts'.
The shift from the 2009/2010 El Nino occurred on Feb
1, 2010 with the 30 day average SOI moving meteorically into
positive territory (starting at -25 and reaching +15 by early May). A false start to the end of La Nina began in 2011 with an equally meteoric drop in the 30 day SOI average the last
week in April 2011, dropping from +30 to +2.0 in a 1 month window, but then all being last as the year drug on. Then another attempt at ushering in El Nino started in Jan of 2012 with the SOI dropping from +24 to -14 by July 1. As such, there were hopes the big drop of the
SOI in the Spring of 2011 would hold or even drop more fueled by successive Active Pulses
of the MJO, but that did not occur. And like 2011, the same thing happened again in the Spring of 2012, though making better long term headway. Over the course of the northern hemisphere summer
the Active Phase of the MJO remained dominant but weak, and when it appeared
it barely reinforced the existing pressure pattern and not
driving it more in favor of a negative SOI. As of today the SOI remains neutral with the 30 days average at 2.58 and the 90 day average at -1.18, and this 2.5 weeks into an Active Phase of the MJO.
Anomalous Equatorial Sea Surface Temperature:
El Nino is characterized by a thin stream of warmer than normal surface
water temperatures extending from Ecuador west over the Galapagos
Islands and onward to a point south of Hawaii or more. As El Nino
matures, the water temps increase and cover more area, typically
peaking in late December. Conversely La Nina is characterized by
the opposite, cooler than normal water temps in the same region and
timeframes. It is the change in water temperature that theoretically
sets up the weather changes associated with either El Nino or La Nina
(though we believe that is more a symptom of greater atmospheric
and oceanic changes already in.cgiay, that enabled the water temp
changes to occur in the first.cgiace). During La Nina a 'Horseshoe Pattern' pattern can develop characterized by La Nina's cold water pushing west on the equator di.cgiacing warm water to the west and positioned both north and south of the cool pool). The Horseshoe is driven by stronger than usual northeast trades winds pushing off the US West Coast and southeast trades tracking off South America deflecting warm water to the west and poleward.
Looking
at current seasonally adjusted equatorial Pacific Sea Surface
Temperatures (SST), the pattern somewhat delineates El Nino.
Warmer than normal water (+1.5-2.0 degs C) is pooled up along the immediate coast of Ecuador streaming
west confined to the equator but loosing heat as it tracks towards the Central Pacific with remnants reaching to the dateline. A
closer inspection reveals small pockets of neutral temp water
tracking west through the heart of the warm pool becoming more coherent on the dateline. These pockets were not present in July and early August, but started appearing in late August and have not dissipated, suggesting weakness in the warm pool if not the beginning of it's outright demise. Still, the overall pattern reflects a patterns consistent with a very weak El Nino. This is a very large step forward from 2 years dominated by cooler than normal waters in the equatorial East Pacific, and will undoubtedly have some positive impact on the Winter storm pattern. and there is some hope for reinforcements arriving in the form of Kelvin Waves (see below).
The other good news is the absence of the 'Horseshoe Pattern'
typical of La Nina. But a remnant of the Horseshoe are still present in the form of a pool of cooler than normal water extending from Central CA over Hawaii. It is being generated by stronger than normal high pressure off the California Coast which is driving stronger than normal trades which in turn cause
upwelling resulting in colder than normal water temps. A secondary more El Nino like symptom is warmer
than normal water tracking from Japan east to within 1000 nmiles of California. Also warmer than normal water has tracked up the Mexico and Baja coast reaching up to Pt Conception CA. But it does not have enough support to round the corner up into Central CA. In all water temperatures reflect what is occurring in the air above them, and the data suggests a hybrid configuration, with elements of El Nino developing but not dominating, and also elements of La Nina lingering and not yet able to be erased.
Wind Anomalies: Trade
winds over the equatorial Pacific typically blow east to west, towards
the Philippines and New Guinea, stronger during the spring and summer
and less so in the Fall and Winter as low pressure starts building in
the upper latitudes with cold front sweeping south towards the equator. During El Nino years and during the Active Phase of the MJO, rather than blowing east to west,
they blow west to east, or at least blow less strong than
normal, which has the same effect as a
reversal of trades in that it supports the generation of a Kelvin Wave
(more below). When trades are suppressed, this reduces
the amount of upwelling along equatorial Central America, allowing the collection of warmer water there (El
Nino).
Conversely stronger than average trades there increase
upwelling producing
cooler than average waters (La Nina).
A
Westerly Wind Burst (WWB) is
an stronger than normal extended duration of wind that blows from west to east along the
equator over the West or even Central Pacific, contrary to normal trade
winds and
forcing warm surface waters to start moving in the same direction as
the wind (details below), a hallmark of a strong Active Phase of the
MJO and a precursor to El Nino. Historically if either El Nino or a
strong burst of the
Madden-Julian
Oscillation is in-effect, trade winds that normally blow from east to
west reverse themselves and blow west to east. That is, when the MJO is
in an Active Phase, the trades reverse themselves in the West Pacific,
and when the MJO is not active, trades return. During El Nino years the the
MJO still has Inactive Phases, just not as prolonged or strong. Conversely during La Nina there are Active
Phases, but they are not as strong or long in
duration.
The continued presence of the Active Phase of the MJO over the Spring, Summer and into early Fall has dampened trade winds over the equator. When the MJO is Active over the Pacific, trade winds have faltered. And when the Inactive Phase was gotten a foothold, trades have been enhanced. The good news is the Active Phase has dominated for much of the year, but mostly very weak when it is in.cgiay. As a result upwelling has been suppressed in the equatorial East Pacific supporting the buildup of warm water there.
Of some interest is what appears to be a modest but long lasting WWB that started 9/2 near 150E and is still in.cgiay as of 9/26. As far as WWBs are concerned, this is an impressively long one, though not particularly strong. The hope is it will support some form of Kelvin Wave driving more warm water eastward.
Pacific Isotherm: Another
key indicator in the evolution of either an El Nino or La Nina
event is the depth and profile of the 20 degree isotherm (thermocline).
During La Nina events, warm subsurface
water remains pooled up in the far equatorial West Pacific while cold
surface and subsurface waters dominate the East Pacific, resulting in a
steep angle from east to west, or from a shallow pool of warm
waters
in the east to a deeper pool of warm water in the west. In El Nino
events, warm subsurface water (i.e. Kelvin waves - more below) migrate
from the West Pacific to the East and the angle flattens with the
depth
of warm water becoming more uniform across the width of the equatorial
Pacific. During
El Nino events though the MJO signal is weak, it appears
that the Active Phases of the MJO are more productive than the Inactive
ones. That is warm water
that successfully makes the multi-thousand mile subsurface journey east
to Ecuador erupts to the surface just off the coast there, and
weaker than usual trades then blow the warm surface water off to the
east, also radiating north up the Mexican coast reaching into
California during significant El Nino events. This results in a pool
of warm water forming off Central America rather than it's usual.cgiace
in the West Pacific, flattening the angle of the 20 degree C
isotherm across the equatorial Pacific. At this time a La
Nina pattern is clearly in control with cool water dominating in
the east and no sign of warmer than usual
waters pushing east towards Central America to flatten
the isotherm
angle.
Subsurface
water profiles for months now have indicated a pocket of blocking cool water that sat down 150 meters below the surface near 130W for nearly 2 years broke up during the Spring of 2012 and has been held at bay ever since, allowing a steady flow of warmer than normal subsurface water to migrate east and erupt along the Central America coast, resulting in the warm surface pool now present there. But the lack of any WWB (over the past 2.5 months) has severely limited the intensity and volume of warm water flowing through this pipe. Regardless, the pipe remains open and the profile clearly supports the flow of warm subsurface water eastward. This is in stark contrast to the
wave-after-wave pattern of warmer
than normal water that tracked east through this region fueling the
2009-2010 El Nino. In contrast, it is just a steady trickle this year.
And of some concern, just in the past week a pocket of -2 deg C water has materialized at 140W and 150 meters down, eerily reminiscent of the previous years blocking pattern. No blockage is yet occurring, nor is it expected to. But it could start influencing events and is worthy of monitoring.
Kelvin Waves: A Kelvin Wave is a pocket of warm water that travels both under and at the oceans
surface from west to east reaching to a depth of about 150-200 meters. It is
generated by a burst of strong westerly winds blowing over the equator
(a.k.a. Westerly Wind Burst (WWB) in the West Pacific and is typically
associated with
the Active Phase of the MJO. As the warm surface water gains eastward
momentum by forcing of the WWB, it sinks
near the dateline and travels well under the oceans surface, only to
reappear at the surface when it impacts and erupts along the South America Coast. This
results in the sudden appearance of warm waters along the coast of Peru
and Ecuador. Occasional eruptions are normal. Large and consistent
eruptions are the hallmark of solid El Nino events. The source of
Kelvin Waves, a negative SOI and reversed trades, is directly related
to the strength and frequency of the Active Phase of the Madden Julian
Oscillation (MJO). This weather pattern is responsible for the periodic
strengthening of the anomalous westerly winds in the West Pacific which
drive production of subsurface Kelvin waves, and also drive the SOI
negative.
Currently
there is some data suggesting a weak Kelvin Wave has pushed through the Central Pacific and migrated off the charts to the east, within a few weeks of erupting along the Central American coast. It was 2-3 deg C above normal at depth, and 1 deg C above normal on the surface. This, if it materializes, could help to weakly reinforce the East Pacific warm pool, or at least prop it up some. Of more interest is what is possibly the formation of yet another stronger Kelvin Wave, currently developing in the West Pacific driven by a near month long WWB event (still ongoing as of this report). Stronger than normal westerly winds confirmed to a tight area near 150E have blown on the equator from Sept 2 through Sept 28 and intensified the first week of October, then forecast to fade. But it will take 3 months for the warm water generated by the WWB to reach the East Pacific and bubble upward, or late in December 2012 (assuming it develops at all).
Pacific Equatorial Counter-Current: There
are three currents that run along the Pacific equator. Two run
just abreast (a few degrees north or south) of the equator flowing east
to west driven by the semi-permanent high pressure centers located
in the center of the North and South Pacific.
These high pressure system are what drives equatorial
trade winds too. But sandwiched between them is the Pacific
Equatorial Counter Current, which flows against the two, running
west to east. Satellite based sensors are used to measure the
strength/speed of the counter current. That data can be
analyzed to determine if the current is flowing stronger or weaker
than in years previous. In essence, anomalies in the
current can be detected. A curious fact becomes apparent when
looking at long-term trends: During El Nino years the counter
current runs harder than usual to the east, and during La Nina years it
runs harder to the west. This is what one would expect, especially
since the exact same pattern appears when
analyzing tradewinds.
In January 2012 the current was weak and flowing generally east to west, consistent with the trades. But in February a significant shift occurred, with the current reversing direction and building slightly with strongest pockets in the far West and Central Pacific consolidating more in the Central and East Pacific in March and building. Another eastward tracking pulse occurred in April to early May then followed by a generally weak west-to-east flow, strongest in the Central Pacific through the summer months. By September the currently had almost reversed direction but only very weakly and isolated to the Central Pacific with a stronger pulse of easterly moving water developing in the far West Pacific, likely consistent with the WWB occurring there. The development of the blocking subsurface cool pool (see above) is tracking exactly in sync with the reverse in the current in the Central Pacific.
In all, the current was just reflecting what was ongoing in the air above it.
OLR:
When
El Nino events unfold at the oceans surface, increased
cloudiness/precipitation will develop
in the atmosphere above the warmer surface waters, since warmer water
supports higher condensation rates above it. The presence of consistent
cloudiness or precipitation where it historically shouldn't be is a
hallmark of El
Nino. Satellite based Outgoing Longwave Radiation (OLR) measurements
track reflectivity from clouds over time. The greater the
reflectivity, the less sunlight is being absorbed by clouds. Low
reflectivity
values represent greater cloud absorption.
Current
satellite data
indicates below normal reflectivity over the equatorial West
Pacific, consistent with the Active Phase of the MJO currently in.cgiay there and enhanced cloud cover. This trend has dominated
for months now (except when the MJO turns Inactive).
Analysis: Reviewing
all the data over the past 9 months, the evidence clearly
suggests that La Nina is loosing control over waters of the Pacific. It's demise started in January 2012 and has continued non-stop through the Spring and Summer. It began with the Pacific equatorial counter current
changing direction and the SOI falling, followed by a quick but modest build up of the storm pattern in Feb-March and the return of the Active Phase of the
MJO. Shortly thereafter a pool of warmer than
normal water started to develop over the equator off Ecuador and
building to the west. The blocking pocket of cooler than normal subsurface water 150 meters down between 130-150W
started decaying as warmer than normal subsurface water assaulted it from the west ultimately opening the gate for more warm water to flow eastward.
That pattern has held through the Spring and Summer of 2012.
It is typical for some
some form of weak El Nino-like pattern to develop after a normal 2 year run of La Nina. In fact, this is how La Nina dies and the system moves towards a normal/neutral pattern. The normal timeframe for the change to try and occur is during the Spring. Whether it sticks is dependent upon a great many factors, not all clearly understood. Regardless, it is not unusual to have a few years of 'false starts' before a legitimate El Nino develops.
What occurs in the ocean influences the atmosphere above it. And as the atmosphere responds to changes in the water below it, it reinforces what is occurring in the ocean. A feedback loops results. As of today we are still trying to get the ocean to return to a non-La Nina configuration. We are part way into that process. Warm water is building up slowly in the equatorial East Pacific supported by weaker than normal trades and the occasional weak WWB all driven by more dominant occurrences of the Active Phase of the MJO and weaker instances of the Inactive Phase. But there is much La Nina momentum in the atmosphere. High pressure remains stubbornly lodged off California driving above normal trades there on over Hawaii and causing upwelling of colder water, which in turn reinforces the presence of high pressure. The change in season often helps to finally break up these long standing patterns out of existence. But that is not guaranteed nor completely expected in the Fall and Winter of 2012.
Always
of interest is the effects of El Nino and La Nina on the relative level of the Atlantic hurricane
season activity. Hurricane activity in the Atlantic is inversely tied to the
strength and duration of El Nino and La Nina in the Pacific (inverse teleconnection noted above). A classic
El Nino
produces strong shearing winds over the Atlantic (during the summer it forms) that tear the tops off
developing tropical storms, rendering them weak and ineffective at
evacuating warm moist surface air up high into the atmosphere through
the storms eye. In effect, a hurricane is the atmosphere's attempt to
create equilibrium, or to restore balance to a system that is too warm,
by creating a chimney to vent off the hot air to the upper atmosphere.
So if an an inordinate
number of hurricanes occur in the Atlantic, or if they are unusually
strong, one could conclude that there is a build up of latent heat
energy in the ocean and the shearing effects of El Nino are not
in.cgiay, which suggests at least a moderate La Nina might be in effect.
Looking
at Atlantic hurricane activity during the Summer of 2012, it
was a statistically active season, but nothing over the top in terms of tropical systems making landfall. As of this report 14
tropical storms have formed, 7 of which became hurricanes and 1 of which
became major hurricane (Michael - Cat 3 for 6 hours).
In fact, as of this date this season is the second most active on record, with the second most active year in the 30's(though one could argue our ability to pinpoint tropical system has been greatly enhanced over the past 30 years, somewhat skewing the trend). It does not appear the developing El Nino-like pattern in the Pacific had much if any direct impact on the tropical storm season in the Atlantic. And contrarily, the presence of La Nina the past 2 years in the Pacific has likely done much to improve the environment in the Atlantic for storm formation. Compared to the previous 2 La Nina years, net tropical storm activity was up for the East Pacific, a direct result of warming of the tropical waters there courtesy of the current El Nino-like pattern. No significant storms hit Hawaii, which is a sure sign of a strong El Nino. In fact, non tropical systems even made it intact to the Islands. And in the far West Pacific, there was no evidence of significant incidences of tropical systems recurving to the northeast bound for the dateline. In fact, the trend was for systems there to travel north and move into Asia. But the season is not yet over. Overall, having any tropical system in the East Pacific, much less ones that produced rideable surf in Southern California, was a big step forward compared to the previous 2 years. So clearly there is some localized El Nino influence occurring in the Pacific.
But at a global scale the net impact was not that typical of El Nino. It was more typical of La Nina in the Atlantic and typical of a weak El Nino in the East Pacific. This suggests a hybrid pattern typical of a developing El Nino, not a mature one having much influence outside the East Pacific Basin.
There are multiyear El Nino events, typically associated with the Midoki variety. A Modoki El Nino (Midoki is Japanese for 'the same but different') forms more in the center of the equatorial Pacific (south of Hawaii), in the Nino 4 region, and evolves there, rarely making much eastward headway through it's life and not typically reaching the Ecuador coast. These El Nino events tend to be more weak-to-moderate in strength too, with lesser impact on the northern hemisphere Fall, Winter and Spring storm pattern. They still have an enhancing impact, just not as strong. In contrast the Classic flavor of El Nino starts forming it's warm pool directly adjacent to Ecuador and expands westward as it matures. The environmental impact tend to be more severe. The most recent El Nino's event (of 2009/2010) was of the classic variety, only one of 5 that have occurred since 1980 (82/83, 87/88, 91/92 [debatable], 97/98 and now 09).
Regardless, the strength of a La Nina event often is in direct proportion to the strength of the preceding El Nino. That is, El Nino and La Nina work in a pair. It's almost as if the atmosphere, in trying to establish some form of equilibrium, compensating in a strong a fashion as the event which caused it to go out of equilibrium in the first.cgiace. If one considers El Nino a warm anomaly, then La Nina is the cold anomaly that follows to set things 'right'. Most notable is the massive La Nina which followed the huge El Nino of '97/98. In fact, that La Nina response was so strong it took till 2009 to mount a respectable El Nino event again (though the 2005/2006 El Nino was not too bad). and there were mult.cgie false starts or weak El Nino's prior to that (02/03, 03/04, 04/05).
Models:
Looking at the MJO models, there is little to indicate any extraordinary energy is to be expected from the MJO, with a weak Active Phase currently occurring and a weak Inactive Phase expected right behind starting mid-October into early November. That said, this is a far cry ahead of last years predicament, where the Active Phase was virtually absent and the Inactive Phase was in control. This year has clearly been dominated by the active Phase of the MJO, strongest in the Spring and then weaker during Summer. But predicting the MJO more than 1-2 cycle ahead is notoriously unreliable. It's better to look and the ENSO models.
We've been following the CFS model. The current operational version (CFSv1) has been consistently suggesting near El Nino like water temps (.75 deg C above normal) in the Nino3.4 region (extending on the equatorial Pacific from south of California to nearly the dateline) peaking in the Jan-Feb 2013 time frame. But that seem laughable given all the other data. And this model was deactivated October 1. The newer version of the model (CFSv2) paints a far different story. It depicts a return to neutral temperatures by mid-Jan 2013 almost going slightly negative, then rebounding into weak positive territory (0.3 degs) by Spring. And CFSv2 run with a climatology going back to 1982 suggests temps dipping to -0.4 deg C in late Jan before rebounding into mildly positive territory. Both these outcomes seem far more realistic.
Looking at the entire population of models produced worldwide, the CFS sits on the low end of the consensus. The mid-point trend through all models suggests the peak has already occurred, and that temps will sit where they are through November, then start to slowly fade back to about 0.35 degs C above normal by mid-January then hold there into the Spring. In all, some warming is to hold on, but likely below minimal El Nino thresholds.
Typically La Nina throws all it has
into it's first year of existence, and by the second year, it is
fading, and is normally just a ghost of it's previous
self. Typically the worst time for storm production is
during the second year of a 2 year La Nina, especially in February
as it is moving into the Spring Predictability Barrier and likely
getting ready to turn towards an ENSO neutral or El Nino favored
long term outlook. This is because there is little energy left in the
atmosphere, where it has almost reached a state of equilibrium. It
is at the extremes of the ENSO cycle (strong El Nino or strong La Nina)
where North Pacific Storm formation is at it's best (and of course
always favoring the strong El Nino). But as things settle down and things
move into the no-mans land of a transition towards equilibrium, a
rather stable pattern settles in.
LONG-RANGE NORTH PACIFIC STORM AND SWELL GENERATION POTENTIAL FORECAST
Fall/Winter/Spring
2012-2013 Swell Generation Potential (for California & Hawaii)
= 5.5
Rating
based on a 1-10 scale: 1 being the lowest (small and infrequent winter
surf conditions), 5 being normal/average, and 10 being extraordinary
(frequent events of large long period swells)
Methodology (2010+) :
We are using the same methodology for making long term
predictions since 2010. In
the past we looked solely upon the presence El Nino using the approach
that El Nino typically enhances the size, strength, frequency and
duration of winter North Pacific storms in and around the Gulf of
Alaska, thereby improving the likelihood for large winter surf in
California and Hawaii. And that La Nina typically decrease the size
strength, frequency and duration of such systems. After reviewing
data from many such years, we still believe that to be true in an
absolute sense over the course of an entire season, but also now
recognize that the lingering effects of either a strong El Nino or
La Nina event last far longer than previous suspected (up to 1 year).
So in the Fall and early Winter season directly following a strong El
Nino winter, even though La Nina may be in effect, the lingering
effects of El Nino on the upper atmosphere could have an enhancing
effect on net storm activity. We've are also turning towards the
opinion that strong La Nina events can potentially have enhancing
effects
on net North Pacific storm formation during the Fall
season. The net effect is the more extreme the
divergence away from a neutral state, the greater the propensity for
weather systems to try and return the system to a state of equilibrium
in the form of storms (which create winds and therefore waves). In the
El Nino state, the focus of the storm is centered more upon the
dateline and the Western Gulf of Alaska and the storm track falls south
and lasts longer into the winter season, where in a La Nina scenario
the focus is more on the Eastern Gulf of Alaska with the track being
di.cgiaced to the north and timed more on the Fall and early
Winter. Therefore, as the swell source
moves east, Hawaii becomes a less likely target.
Also
the relative strength of MJO phases have an impact on the transport of
tropical moisture from equatorial regions of the West Pacific northward
to ultimately fall under the influence of the jetstream, increasing the
probability for storm formation moving over the dateline and into the
Gulf of Alaska. So MJO patterns are now considered in the forecast.
In
addition we are become more convinced there is a teleconnection between
storm activity in the southern hemisphere and that in the north 6 months
later. That is, in years where the net storm activity is up in the
southern hemisphere winter (summer in the N Hemi), a corresponding
increase in activity could also be noticed in winter in the northern
hemisphere (6 months later). The only exception is when there is a
strong El Nino or La Nina up north in the winter, then that translates
into a net increase in winter activity in the southern hemi 6 months
later. Most of this focuses on the strength of the MJO, and seeing how
the area it directly impacts is the equatorial Pacific which straddles
both the north and south hemisphere's, it would seem reasonable to have
an impacts at both poles. And
yet one more possible early indicator is the configuration of the
jetstream over the North Pacific starting late July into August over
the North Pacific. There is some evidence to suggests a healthy
consolidated flow over the NPac early in the Fall season might lead to a
continuation of that pattern through the Winter season, and
that if an early season .cgiit pattern develops, it will continue in that mode through Winter and Spring. A .cgiit
Northern hemi jetstream does nothing to support surface level gale
development.
Forecast Conclusion: All data suggests we are in a hybrid state, not really reflecting El Nino nor La Nina either. The lingering momentum from 2 years of La Nina dominate the global scene while a weakly developing El Nino is trying to get footing, but is being dampened by the lingering momentum from La Nina. And based on the models and other data, it seem the El Nino will be all but gone by the time December arrives. In effect, this will be a neutral winter season. Historically it is not unusual to have several years of False Starts to El Nino before it finally manifests itself in full form. In Summer of 2011 it tried to pulse, only to get beat back. And now in 2012 it has done the same, making more headway, but still not being able to round-the-corner from Summer into Fall. Instead it appears to be dissipating and a consensus of the long range models are doing nothing to dispel that outcome.
Two other points of interest: The North Pacific jetstream was di.cgiaced well to the north during July and August, and the storm trend surely reflected that scenario. No recurving Asian tropical systems tracked from Asia over the dateline, or even made a move towards trying to recurve northeast until late September. Since then a somewhat promising pattern has emerged, but not particularly strong. Regardless any recurving systems are a sign of hope and a far cry from the previous 2 years. Historically during decent El Nino years tropical systems in the West Pacific turn hard east, transitioning to extratropical status and build while moving over the dateline towards the Gulf. Another sign is the arrival of a significant class swell in September. Miraculously, a gale did develop on the dateline in late September which produced swell of 7 ft @ 16-17 secs for a few hours in Northern CA (9/24). But that seemed more of an anomaly than a trend. And it's formation was wholly aided by the Active Phase of the MJO being in.cgiay.
In the super El Nino of '97, the first Significant class storm of the year occurred in mid-Sept, an extratropical cyclone resulting in 65 kt winds over a large area aimed east producing swell of 10 ft @ 25 sec solid hitting the California coast on Sept 27. And lesser northwest swell producing systems had occurred as early as mid-August. And even in the El Nino of 2009, the first significant class swell of the season arrived on Sept 12th. Down
south, over the southern hemisphere winter (Northern Hemi Summer), net storm activity was
well below normal and focused on the not-preferred Southeast Pacific.
Only 3 significant class summer time swells resulted for CA, well below normal. And even those were not obvious calls. Based on our previous statement does not bode well for the following Fall 2012 season. If anything, the transition to a normal or neutral state only saps potential storm producing energy from the atmosphere as a sort of equilibrium is established. This is where we find ourselves today.
The good news is that monster high pressure between Hawaii and California has likely peaked and is expected to decay as late Fall sets in. And whatever energy the lingering warm pool in off Ecuador imparts to the atmosphere, (whatever is not negated just trying to kill La Nina) could help to gently fane the flames of the winter storm season. But overall we are not overly optimistic about the coming Fall Winter season. But conversely, we are not over pessimistic either. At least La Nina is fading and warm water is trying to make a respectable showing in the equatorial Pacific.
We
have assigned a swell potential rating of 5.5 for the coming
Fall/Winter season, suggesting a historically 'normal' Winter swell production season. Diving down
to the details, we expect the best odds for swell production to
occur in the December to January timeframe, historically the
peak window for North Pacific storm and swell production. With luck the season could hold into March or so, but not much beyond unless a new warm pulse starts building during the Spring Unpredictability Barrier in March 2013.
During
El Nino events the standard swell profile is for not only more
storm frequency, but stronger and longer lasting
ones producing larger and longer lasting swells. And with the jetstream
shifting south, the swell angle tends to turn more westerly.
Such a pattern was in abundance during the glory
days of the 90's and early 2000's.
Conversely the abysmal surf pattern of 3 year
period between 2006/2007-2008/2009 (the 3 years after the 2005-2006 El
Nino) where we would get one day, or
even 12 hour swell
events, was marked by the presence of La Nina.
For this year we expect an about normal pattern, with modest swell durations with average breaks in-between. Most activity is to be confined to when the Active Phase of
the MJO is occurring, but that will not preclude storm from forming during Inactive Phases, especially since the phases are expected to be rather muted in either direction.
During El Nino years the surf
strategy is
to.cgian for the
long run, with endurance and stamina month after month outweighing
short feasts and 'go-for-broke' assaults. Conversely during a La Nina winter one should
get all you can while you can, cause the odds of it occurring
anytime soon are low.
This year one should follow the La Nina strategy, but save a little in the tank, because we could be surprised.
Regarding local weather in CA: During El Nino years one
expects more moisture than normal with increased snow pack levels
in higher elevations of the
Sierra on into Nevada and Colorado. El Nino tends to shift the
jetstream southward and flat over the continental US with the
California high pressure system retreating south and west more
than normal if not evaporating completely, favoring
precipitation for the more southerly positioned ski resorts in the
Southwest. But it too causes surface temperatures to rise with a larger
amounts of warmer tropical moisture in the mix, meaning the
freeze line rises (in elevation) with increased odds for
rain at lower lying resorts. But for La Nina years, the
California High pressure tends to take over the waters off the coast
there with the jetstream focused on the Pacific Northwest (Central
Oregon northward). It is not unusual to have much larger volumes of
moisture up there if not outright flooding while a virtual lack of
rainfall occurs down into California, especially from Monterey Bay
southward. The exact north-south position of the dividing line varies
significantly from event to event. Of note, during La Nina years, when moisture does move into the California region, and assuming there is sufficient snow base, there is a higher than normal tendency for it to be driven by backdoor fronts, those tracking directly down the Pacific Northwest coast. They tend to be colder and drier, and when they do arrive, the snow quality is exceptional with bone dry power the result. They are not common, and like the surf profile, come only occasionally. So the strategy during such events is to get it when it comes and not expect more to follow directly.
For the 2012-2013 season, expect somewhat less precipitation than normal, with a late start to the snow and rain season. High pressure has ruled supreme off the CA coast for 2 years now, getting particularly entrenched in 2012, and there is no sign of it abating anytime soon. The good news is lingering light high pressure could make for many pristine offshore days along the coast, with storms organizing on the dateline but getting deflected north as they approach the coast. This might set the potential for somewhat smaller surf, but it will be well groomed upon arrival. if anything Hawaii, might be better set up to catch whatever swell is produced, And it too will have the benefit of trades and offshores versus rain and Kona winds.
As always, this
is a
preliminary assessment, based on what is known at this time and does not guarantee any particular outcome.
And there
remains the nagging question of whether we have
moved into the Inactive Phase of the Pacific Decadal Oscillation
(PDO). The PDO is in-effect a 20-30 year cycle of weather than
slightly mirrors El Nino in the active phase and La Nina symptoms in
it's inactive phase. Our thinking is that if we are in-fact in the
inactive phase of the PDO (probably since 2000, and will be for the
next 20 years), then the odds for favorable winter storm generation
conditions are stacked more in favor of La Nina than El Nino, since the
inactive phase of the PDO mimics a weak La Nina. But this is mostly
just pure speculation. And there is other data that suggests that
we we're only been in a 'corrective pattern' since the big 97/98 El
Nino. Since that ENSO event was so large and strong, the atmosphere had
been trying to re-establish some form of equilibrium for nearly a decade
since, and the 2009/2010 season was the first chance since then for a normal pattern to
manifest itself. Our thoughts are the historical record is too
short and it too soon to know with any certainty whether we
are in a down phase of the PDO.
The other consideration is though the atmosphere is not in a true El Nino state, might we are approaching a year or two run in a slightly warm state, perhaps a Midoki state, as part of the run up to a true El Nino a few years out. This is the preferred option. A slow but steady run-up to an El Nino sets the entire atmosphere in motion slowly moving towards El Nino, and builds much momentum year to year, significantly enhancing the storm track and net storm activity both in summer and winter but without all the negative affects of a full blown El Nino. There is no evidence to suggest that this is in-fact occurring other than the models suggesting slightly warmer water temps in Spring of 2013. But a few False Starts to El Nino typically result in such a configuration.
So assuming a fading La Nina in.cgiay and
a weak El Nino/False Start trying to get footing, we
calculate net storm activity will be
about normal with the best support for storm formation occurring during Active Phases of the MJO in the Dec-Feb 2013 timeframe.
Swell producing Pacific storms will be average in
duration and average in intensity with the
potential to cover normal surface area, resulting in normal sized fetches of average duration and intensity. This
should result in
statistically normal surf in terms of consistency, period and size. And swell direction will be di.cgiaced slightly to the north (295 degs relative to NCal).
(This
forecast is highly speculative and based on historical analysis of past
La Nina/El Nino events and the latest long-range forecast models)
Sea Surface Temperature Anomalies
Courtesy: NOAA OSDPD
Notice the broad but somewhat diffuse area of warmer ler than normal water
temperatures (orange shades) extending along the equator from
the Ecuador all the way to the dateline. This is the result of decreased trades and Kelvin Waves errupting along the coast of South America and is the hallmark sign of El Nino. Temps were much higher in July, but are subsiding. Also notice some warm water
has built up near Japan extending east almost to the US West Coast. But of concern is the cooler than normal water (blue shades) extending from the US West coast over Hawaii to the dateline, a hangover from La Nina and generated by higher than normal pressure and increased trades over the North Pacific.
.
Sea Surface Temperature and Surface Wind Anomalies on the Equatorial Pacific
Courtesy: NOAA PMEL
In the top image notice trades wind blowing firmly east to west over
the width of the equatorial Pacific. But also notice reversed
trades (west winds) associated
with the Active Phase of the MJO and a Westerly Wind
Burst (WWB) over the equator in the far West Pacific. This is occurring during the Active Phase of the MJO and will help to generate a Kelvin Wave. In the
lower panel
notice that surface water temps are slightly above normal over most of the equator. The arrows indicate the
strength and direction
of wind anomalies, which are trending towards a neutral trade pattern in the East and a full reversal in the West.
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20 Degree Thermocline Depth and Position Time Series
Courtesy: CPC NCEP NOAA
(Top Image) The core of warm subsurface water is centered just west of
the dateline and making some indication of moving east, but not remarkable.
(Lower Image) Notice the building pocket of warmer than normal water (1.5
degs C above normal) at 175W and 100 meters deep. This pocket is
building and moving east symptomatic of an eastward moving Kelvin
Wave (warm subsurface water) traveling from west to east. Another Kelvin Wave is moving east off the right of the chart.
.
Equatorial Pacific Sea Surface Temperature Forecast
Courtesy: NOAA/NCEP
Notice that the average of many separate runs of many
models generally suggesting warmer than normal
waters well off Ecuador and slowly settling back to a normal pattern by March 2013 consistent with a weak El Nino at best.
.
Southern Oscillation Index (SOI)
Courtesy: BOM
The SOI depicts the difference in pressure between Tahiti and Darwin
Australia.
When it is consistently negative (that is surface pressure is lower in
Tahiti
than Darwin Aust), the trend is towards El Nino. And when it is
positive
the trend is towards La Nina. Notice the big dip into negative
territory that started in early 2012 (indicative of a developing El Nino). But alos notice that it has rebounded hovering on average in neutral terriroty more recently.
Small pauses or fluxuations in the trend occurred as the Active
and Inactive pulses of the MJO move over the West and Central Pacific
at 30-45 days each. Dips are the Active Phase
of the MJO and rises are the Inactive Phase.
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Pacific Countercurrent Anomalies
Courtesy: OSCAR/NOAA
This image depicts the zonal flow of the Pacific Counter current, which
runs roughly on the equator between the West and East Pacific. The top
panel depicts the absolute flow of the current. When it runs east
to west as it normally is (blue arrows), this means nothing, unless is
is strong, then that suggest La Nina. When the flow reverses and
moves west to east (red) that suggest El Nino.
The bottom panel depicts anomalies in the current as compared to
historical and seasonal averages. Departures from normal
are clearly obvious, with strong red arrows reflective of El
Nino and strong blue of La Nina. The images suggest a hybrid state with a weak La Nina signal with easterly anomalies in the Eastern Pacific and
a strong El Nino/Westely Wind Burst signal occurring west of the dateline.
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