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El Nino Southern Oscillation (ENSO) Forecast

Issued: 11/07/2011
Updated as Warranted

See ENSO page for Links and Current Data
ENSO Archives

La Nina Dominates
No Respite Forecast Through Early 2012

Overview: Following on the heels of the El Nino winter of 2009/2010, La Nina starting brewing in early March 2010 and continued strengthening through the end of the year, wrapping into 2011 and remaining solid into the last week of April when it peaked with 30 day average Southern Oscillation Index (SOI) values to +30.  At that time a massive pulse of the Active Phase of the Madden Julian Oscillation (MJO) set in driving the average down to just shy of 0 in a short 25 days, almost making it look like La Nina was going to fade out and El Nino move in complete with a Kelvin Wave washing across the equatorial Pacific and the requisite warming of surface waters off Ecuador. But contrary to to initial observations, the SOI slowly fought to regain positive footing through the summer of 2011 on into the early months of Fall, with the Inactive Phase of the MJO pulsing in August and then again October pushing the 30 average back to 10.  This was a long ways from the peak achieved in April, but an equally long ways from being in El Nino territory.  

Under the influence of La Nina, the 2010-2011 winter surf season for the North Pacific peaked out with 6 significant class storms (well below normal), of which only 2 were of any real notice. But contrary to expectations, a consistent storm track fell out of the Gulf of Alaska and down the US West Coast providing cool temperatures and serious accumulations of precipitation at higher elevations resulting in record snowpack for the Sierra.  And follow-on cold weather held the snowpack in-place well into the end of July (2011). The seasons appeared to be displaced 6 weeks behind normal. 

The MJO sat near dormant for the balance of the summer and if anything pulsed only in the direction of the Inactive Phase.  But surprisingly, the Southern Hemisphere produced a solid series of 7 storms, with the peak being a large system that traversed the entire South Pacific late in August with 60 kt winds and seas to 52 ft resulting in large long period swell pushing up into all Northern Hemisphere summer breaks. And an interesting start to Fall produced a rather early series of gales pushing into the US West Coast, with near 3 ft of snow in the Sierra in early October and 1 near significant class swell resulting.  We've been holding off producing a long term forecast pending arrival of the true Fall-Winter 2011-2011 weather pattern, but as of this writing the existing pattern has held solid, suggesting the October snow was not an anomaly.  We also wanted to allow sufficient time for the 6 week seasonal delay to pass, which we now believe it has.    

It is with that background that we look to the coming Fall and Winter of 2011/2012 with below normal 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, and it's state during El Nino and La Nina years. It is followed by an analysis of how that feature is currently behaving. Once all features are analyzed, 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 implicated 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 implicated 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 Inactive Phase since July and no serious Active Phases have been evidenced since then.  Weak Active Phases occurred in June and August, but did nothing to push the pattern more towards even a neutral state and instead only reinforce the pattern that was set in May.  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. 

Just as the shift from the 2009/2010 El Nino occurred on March 1 2010 with the 30 day average SOI moving meteorically into positive territory (starting at -25 and reaching +15 by early May), a equally meteoric drop in the 30 day average occurred starting the last week in April 2011, dropping from +30 to +2.0 in a 1 month window. This time period is called the 'Spring Unpredictability Barrier'.  During this time frame (roughly March to May) often 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. As such, there were hopes the big drop in the SOI would hold or even drop more fueled by successive Active Pulses of the MJO.  But over the course of the northern hemisphere summer the Active Phase of the MJO remained weak, and when it appeared barely reinforced the existing pressure pattern and not driving it more in favor of a negative SOI.    


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 play, that enabled the water temp changes to occur in the first place). 

Looking at current seasonally adjusted equatorial Pacific Sea Surface Temperatures (SST), the pattern somewhat delineates La Nina. Warmer than normal water (+1.5 degs C) extends off Ecuador streaming west over the equator to a point about south of California. But a closer inspection reveals pockets of cooler than normal water tracking west through the heart of the warm pool and then amplifying near 120W  continuing west over the equator to the dateline and almost to New Guinea.  Temperatures were dipping -1.0 degree below normal over that expanse with perhaps pockets a little cooler. This is the classic signature of La Nina.  It should be noted that the solid pulse of the Active Phase of the MJO in late April-May set up a Kelvin Wave that in-turn produced the warm waters still lingering off Central America. And subsequent weaker Active Phases in June and August tried to reinforce that warm pool, but without much luck. And even more telling was feeder bands of cooler than normal water, resulting from upwelling, were occurring, streaming off the California Coast heading southwest and joining the main flow south of Hawaii to the dateline and another mirror image flow pushing from off Chile and Peru tracking northwest to the same junction just east of the dateline.  This was the hallmark 'Horseshoe Pattern' typical of La Nina and is driven by stronger than usual northeast trades winds pushing off the US West Coast and southeast trades tracking off South America. These winds are presumably being driving by stronger than normal high pressure in both the north and southern hemispheres of the Pacific which in turn cause the upwelling and colder than normal water temps.  Conversely warmer than normal water was pooled up in the far West Pacific and Indian Oceans and also displaces into the Northwest and Southwest Pacific Ocean.  This is effectively the same setup as last time this year, only not quite as strong.  And the presence of any warm water off South America in the Pacific is a step in the right direction.  But it is clear the upper level wind circulation still very much favors enhanced trades and easterly wind anomalies (blowing east to west) over the equatorial Pacific which is symptomatic of La Nina.  

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.  Clearly we are in a La Nina regime with very little evidence of significant trade reversal or WWB's since the April-May pulse (during the Spring Unpredictability Barrier).  

Wind anomaly analysis for Summer and Fall 2011 indicate that on average trades over the equatorial Pacific have been blowing stronger than normal east to west. There is clear evidence of upwelling (colder waters over the equator and flowing off the US and South America. and even though the velocity may not be exceptional, the duration of those trades has been relentless, resulting in the cold water pattern discussed above.  It is that 'duration' that would be a trademark of stronger than normal high pressure in both hemispheres of the Pacific. That is, high pressure tends to produce not strong winds, but steady winds.  Conversely low pressure produces gusty-uneven winds.  To generate massive upwelling, one would require the presence of solid unrelenting high pressure. That appears to still be the case for the Pacific

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 place 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 consistent small pocket of warmer than normal water in the the far West Pacific under the equator down at 150 meters ranging near 2 deg C above normal and holding steady. And a modest pool of cooler than normal water (-3 deg C) has remained present between 120-140W at a depth of 100 meters.  This cooler water has been locked in-place since the one Kelvin wave that passed through here in May 2011. The cool pool has not really gotten any cooler nor grown in size, but appears to be acting like a brick wall preventing any warm water from encroaching east.  The assumption is that no Active MJO pulse has developed with enough force to set up a decent Kelvin wave to move in and dislodge the cool pool. This is in stark contrast to the wave-after-wave pattern of warmer than normal water that tracked east through this region during the 2009-2010 El Nino.  

Kelvin Waves: A Kelvin Wave is a pocket of warm water that travels under the oceans surface from west to east at 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 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 no data to indicate that any Kelvin Wave activity has occurred since about May of 2011 and if anything, even if one were to try and form, it's eastward progress would be blocked by the pocket of cooler than normal water south of 120W on the equator.

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. 

Looking at recent data the current is running stronger than normal towards the west, a clear signal of La Nina. It is strongest over the East Pacific but still is tracking west over the entire length of the equator. A month previous it was in effect doing the same thing, and also the same the month before that (Aug). No surprise there. But looking further back starting about March 10-15 (2010) the current changed direction, from flowing anomalously west to east switching to east to west. This was the time we switched from a El Nino regime towards a La Nina regime. Looking back one year to the summer of 2009, the current was flowing steadily west to east and biased in favor of El Nino. Then in March of 2010, it suddenly reversed direction, the SOI started it's race to positive territory, and the storm machine shut down in the North Pacific.  We started looking month by month from 3/2010 forward and found that the typical east to west flow was in control through Dec 2010.  Then in January a reversal set in with the current running steadily west to east, holding solid through the Spring to early June before starting to subside.  We are wondering if this possibly was a precursor to the big Active Phase Push and subsequent Kelvin Wave that occurred in May 2011. Regardless, by July the current started to weakly reverse itself (flowing east to west), and has continued ever since (through Oct 2011).         

Looking at the time of year the current changed for El Ninos in the past (the record starts in '93), most started at least 3-4 months into the year. In these previous events (including the record year of '97) it was not really till the Fall months that the current bloomed to it's full potential.  And interestingly most had some sort of a pause or significant decline in the flow in the July/August timeframe, before the final push into Fall (except 2006).  In many cases, the current changed before the SOI dropped for the first time that year into it's first run of sustained negative numbers (i.e. the first Active Phase of the year): 2002 current change was Feb 1/Negative SOI starting mid-March, 2006 current change mid-Feb/SOI early May, 09 current mid-Jan/SOI negative late April/though dropping since Feb. 1994 was excluded from the review because it appeared that a multi-year ENSO event was occurring, carried over from '92/93.   This is relatively new data and the record is very short, so no solid conclusions can be drawn, but it provides some foresight for future research. If nothing else, it seem that during the Spring Unpredictability Barrier, the Pacific Counter Current seems disposed to  changes in flow and the SOI seems to make significant changes as well. 

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 an above normal reflectivity over the equatorial West Pacific for this time of year. This trend has been consistent for months now (except when the MJO tries to turn Active, and the only fleetingly)  and is certainly an indicator of the Inactive MJO phase were are currently in and the broader Inactive pattern that continues to dominate.  

Analysis: Reviewing all the data over the past several months, the evidence clearly suggests that La Nina continues to have control over the Pacific. It started in the Spring of 2010 with the Pacific equatorial counter current changing direction, followed by a meteoric rise in the SOI with a quick decay of the storm pattern and the rise of the Inactive Phase of the MJO. Shortly thereafter a pool of cooler than normal water started to develop over the equator off Ecuador and started building to the west. Then a pocket of cooler than normal water started building 100 meters down under the equator south of Hawaii. That pattern held through the winter of 2010-2011 and never gave up an inch until late April 2011.  Prior to that (starting Jan 2011) the Pacific counter current changed direction (west to east) and flowed solid, possibly enabling a solid pulse of the Active Phase of the MJO to take root forcing trades to reverse and allowing a Kelvin Wave to track into the East Pacific, setting up warmer waters off Ecuador and almost taking the legs out of La Nina. But by then the current had returned weakly to it's normal configuration starting in June and has held it's own since.  As a result the Inactive Phase of the MJO has dominated, with only weak iterations of the Active Phase making a showing in June and August. In short, a La Nina dominated pattern has continued to persist with virtually no evidence to suggest any sort of an El Nino pattern was to return (other than the brief glimpse of hope in May).  

But none of this is unexpected. Typically some form of La Nina always develops after a run of El Nino, and so we were due after the 2009-2010 El Nino.  There have been multiyear El Nino events, typically associated with the Midoki variety. A Modoki El Nino (Modoki 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 Ninos 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 place.  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). Given the 'rubber band' postulation above, we are expecting a pretty firm multiyear La Nina response as the atmosphere tried to rebalanced after the 2009/2010 El Nino. 

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 sumer 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-play, which suggests at least a moderate La Nina might be in effect. 

Looking at the Atlantic hurricane activity during the Summer of 2011, it again was a statistically active season, but nothing over the top. 17 tropical storm formed, 6 of which became hurricanes and 3 of which became major hurricanes. Of most interest to the US was hurricane Irene which reached Category 3 status on 8/24 (120 mph winds) then faded while pushing into North Carolina raking the Northeast US Coast. Like the year before, most storms took a track to the north before reaching the US Eastern Seaboard. We had actually expected more from this season. The previous years hurricane season was hampered by lingering effects of the previous El Nino. But no such lingered effect remained for 2011. 

Models: Looking at the MJO models, there is little to indicate than any significant pulses of the Active Phase of the MJO will result in the next few months. The Active Phase of the MJO was virtually absent for much of the summer, or when it did appear, it was weak. The Inactive Phase has dominated.  That said, normally during La Nina events there are supposed to be occasional big swings between the Inactive and Active Phases of the MJO. And with those Active Phases, increased support for storm development in the North Pacific. 

Some ENSO models suggest we are going to see a regeneration of La Nina during late Winter/early Spring (i.e. Jan-Feb 2012). If this occurs, then there would be increased potential for perhaps a solid Active Phase from the MJO and then maybe a good but short run of storms in the North Pacific.  But that assessment is a minority opinion and seems highly unlikely.  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 we move into the no-mans land of a transition towards equilibrium, a rather stable pattern settles in. We suggest that is the pattern expected for the 2011-2012 Winter into Spring.  

LONG-RANGE NORTH PACIFIC STORM AND SWELL GENERATION POTENTIAL FORECAST

Fall/Winter/Spring 2011-2012 Swell Generation Potential (for California & Hawaii) = 2.5
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 (2011) : We are using the same methodology for making long term predictions as in 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 displaced 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 split pattern develops, it will continue in that mode through Winter and Spring. A split Northern hemi jetstream does nothing to support surface level gale development.

Forecast Conclusion: All data suggests that a moderate strength La Nina was in-play starting in the Fall of 2010, continued through Winter, tried to make a correction in the Spring of 2011, but then fell weakly back into a La Nina mode in the early Fall (2011), and is slowly trying to continue on that path. If anything, we expect it to get mildly stronger as we move into the Northern Hemisphere winter, but not overly so. The presence of colder than normal waters over the balance of the equatorial Pacific, the locked in Horseshoe Pattern over the North and South Pacific, a weakly positive SOI, and a moderate pool of cold water below the equatorial Eastern Pacific and a near total lack of any real Active Phases of the MJO for months now supports this conclusion. The buildup of warm water in the Atlantic and a reasonably active hurricane season there only adds to the conclusion. And there is no evidence to suggest that any reversal of this trend is at hand. Historically La Nina events last 2 years, peaking out in December of the first year with effects on the environment holding well through Spring, and if strong enough, affecting Summer and Fall of the following year (or potentially longer if recent insights in to the effects of ENSO events over a global scale are correct). 

Down south, over the southern hemisphere winter, net storm activity was above normal and focused on the preferred Southwestern Pacific. This is not explainable using our regular forecasting techniques. But there was a significant increase in tropical and monsoon activity in the Central and Eastern Indian Ocean during the northern hemi Summer and Fall of 2011.  And the total lack of any real MJO activity in the Pacific (and if anything, a persistent Inactive Phase pattern locked over the West Pacific) tends to suggest that a semi permanent Active Phase was locked over India and Indonesia.  In short, the MJO, rather than traveling around the globe, was locked in a 'standing wave' pattern focused on the Indian Ocean.  And it was the poleward storms that indirectly were enhanced by this standing wave, that developed in the Southern Indian Ocean and traveled east from it, surviving the journey into the Southwestern Pacific resulting in 7 significant class storms/swells occurring with a series of smaller utility class swell mixed in, focused well on Hawaii with still good exposure to the US mainland. 

The North Pacific jetstream pattern remained reasonably good in August and September, in that it was not split and had reasonably good velocity associated with it.  But it was displaced well to the north averaging over the Aleutian Islands.  Still a couple of early season swells managed to move into the Northern CA swell window, but mostly from a rather northern direction sending only limited sideband energy towards Hawaii. 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.  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 2009, the first significant class swell of the season arrived on Sept 12th. Clearly that was not the expectation this year, and it did not occur. In fact, as of 10/31, we're still waiting for the first 'real' significant class storm of the season. 

We have previously postulated that stronger La Nina events have the potential to positively impact the production of Fall and Winter storms, but then went on to state we didn't clearly understand if that was the case or whether since strong La Nina events tend to follow stronger El Nino event, that it wasn't just the hangover from El Nino doing the influencing.  For the Fall and winter of 2011, that will not be a factor. We are well past the point where the 2009-2010 El Nino will have any impact, and past the point where the early energy of a building La Nina will have any influence either. If anything we are being extra vigilant monitoring the jetstream to see if it will move into a split mode resulting in the storm track rapidly faltering. If this were to occur, it would likely happen during an Inactive Phase of the MJO and start sometime in late January or early February 2012, as Winter passes it's peak and a real malaise in terms of storm production starts to take hold.  But looking at recent model data, it seems that such a jetstream split is just starting to make an appearance over the East Pacific.    The net result would be strong high pressure down at the oceans surface, especially in the Northeast Pacific, setting up brisk north winds raking the California coast and strong easterly trades pushing into Hawaii. We had expected this to occur in the Spring of 2011, but it did not.  But we suspect we will not get so lucky this year.            

We have assigned a swell potential rating of 2.5 for the coming Fall/Winter and Spring season, suggesting far less than average odds of a historically 'normal' Winter swell production season. Diving down to the details, we expect the best odds for swell production to occur in the November to early January timeframe, historically the peak window for North Pacific storm and swell production.  A rapid decrease is expected as the season moves on, with next to no activity once we reach mid February 2012, with colder than normal air and water temps and an early and strong Spring signature setting in (i.e. brisk cold north winds). 

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 believe that will be the case as well, with short lived-swell durations with long breaks in between, through not so much that way during November and December (2011), and especially during the Active phase of the MJO, but increasingly moving toward that pattern as the season progresses.  So if during El Nino years the surf strategy is to plan for the long run, with endurance and stamina month after month outweighing short feasts and 'go-for-broke' assaults, this seasons strategy should be to get all you can while you can, cause the odds of it occurring anytime soon again will be low. 

The weather will also play a factor 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. Clearly 2011 was an anomaly, with copious precipitation occurring well down into Central CA (Mammoth Mountain) but still coming from a more northerly direction typical of La Nina rather than direct out of the west typical of El Nino.  Under normal La Nina conditions from a ski and boarding standpoint, going north would be the recommended strategy (Oregon northward).  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 is to get it when it comes and not expect more to follow directly. 

That said, the 2010-2011 La Nina winter was exemplified by the core of the Northeast Pacific high pressure system being positioned a bit west of normal (for a typical La Nina year).  So rather than the high ridging hard into the Southwest US Coast, it actually remained just offshore, allowing an incessant flow of cold air and moisture to fall down the coast (i.e. backdoor fronts), resulting in tremendous accumulations of dry snow.  For the Fall of 2011, that pattern has again manifest itself. There is already total ground coverage at most Sierra resorts highly reminiscent of last year, and highly unusual for early November.  And long range models suggest that at least normal precipitation amounts could be expected into the early Winter for the Southwest US.  Perhaps the exact position of the Northeast Pacific high will remain offset just a bit to the west, with another good snow year possible. But that is mainly a highly speculative guess at this early date and has no bearing on surf generation potential.

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 have 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.  

So assuming a moderate plus strength La Nina in-play and expected to hold Winter and early Spring of 11/12, we calculate net storm activity will be significantly less than normal, with the strongest La Nina component occurring in early February. Swell producing Pacific storms will be shorter in duration and less intense than normal with the potential to cover less surface area, resulting in generally a smaller fetch of decreased duration and less intensity. This should result in less consistent, smaller and shorter period surf, similar to the 3 year period from 2006-2009.  And the swell direction will be displaced well to the north.      

(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 area of cooler than normal water temperatures (blue shades) extending along the equator from the Ecuador all the way to the dateline. Notice some warm water has built up on either side of the equator off South America, the result of a Kelvin wave that impacted the region in May, with subsequent weaker pulses in months afterwards.  But they were not enough to wipe out the more dominant cool flow. Also notice the concentration of cool waters extending from California southwest over Hawaii reaching to the dateline, at -1.0 degs C below normal with a mirror image flow pushing off Chile tracking northwest.  The production of these cooler than normal surface water temperature is driven by stronger than normal trades winds blowing east to west (or if not stronger, at least with more duration than normal). Both these are the product of stronger than normal high pressure in the North and South Pacific causing  enhanced trades, upwelling and hence the colder water temperatures. Also notice the warmer than normal waters temperatures in the Central Atlantic, the result of less than normal trades there and less upwelling and more stagnation, allowing heating to occur. 

SST Anomoly

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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. This pattern has been unrelenting all year. There has been no evidence of reversed trades associated with the Active Phase of the MJO or a Westerly Wind Burst (WWB) except in late April into May (2011) and for short durations during subsequent Active Phase pulses in late June and August. In the lower panel notice that surface water temps are above below normal in the area on the equator near 130W (off the South American coast)  The bulk of the temperature departure is focused from south of Hawaii to south of California with temperatures -1.5-2.0 deg C below normal. The arrows indicate the strength and direction of wind anomalies, which are trending towards an enhanced trade pattern in the West and near neutral)(normal) in the East.  There is no evidence of any west to east blowing winds (WWB). 

SST Wind Anomoly

 

20 Degree Thermocline Depth and Position Time Series
Courtesy: CPC NCEP NOAA
(Top Image) The core of warm subsurface water is centered well west of the dateline and making no indication of moving east, symptomatic of La Nina. The thickness of the depth of warm waters in the east is almost non-existent with all warm water off to the west, another indicator of La Nina.
(Lower Image) Notice the pronounced pocket of cooler than normal water 
(-3 degs C below normal) at 120W and 100 meters deep. This pocket is stationary and has been in place for over a year now.  It is slowly easing east and getting warmer (it was -7 degs C below normal last year at this time), but is still blocking the flow of warm water from the west to the east. There is no evidence of any Kelvin Waves (warm subsurface water) traveling from west to east 

SST Depth

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Equatorial Pacific Sea Surface Temperature Forecast
Courtesy: NOAA/NCEP
Notice that the average of many separate runs of many models generally suggesting cooler than normal waters forecast off Ecuador through March 2012, consistent with the ongoing evolution of a moderate La Nina.

SST Forecast

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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 in 2009 (indicative of El Nino occurring then) and then the the big upward trend starting in March 2010, from -25 to +25, indicative of La Nina. A big drop occurred in late April/early May 2011 during the Spring Unpredictability Barrier.  But  it is slowly trying to push back into more positive territory indicative of a continuing La Nina. Small pauses or fluxuations in the trend occurred as the Active and Inactive pulses of the MJO moves 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. 

SOI



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 generally weak La Nina signal with easterly anomalies in the Eastern Pacific and far West Pacific with a faint westerly push near the dateline.   

Pac Current


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