What
source data is used to construct the buoy forecasts? Stormsurf
buoy forecasts provide you with the most detailed and accurate
swell and surf forecasts available. To acco.cgiish this, we use
site specific bulletins from the regional runs of the operational
NOAA Wavewatch III wavemodel. The advantage of these bulletins
is they detail the swell height, period, and direction for each
individual swell converging at predefined locations across the
globe for up to 6 different swells. The downside is they don't
provide as much global coverage as the other major option: GRIB
data. But GRIB data suffers in that it only provides information
about the dominant 'swell'. If the dominant 'swell' is a windswell,
even though smaller but more energetic secondary groundswell
is present, the GRIB data will not recognize the groundswell.
The paradox is that often the smaller but more energetic groundswell
will produce larger waves. From a surfing perspective, period
is more a determiner of wave size than swell height. It is for
this reason that we felt compelled to use the bulletins, because
of their ability to ferret out with a high degree of accuracy
high energy swells. The bulletins have excellent coverage for
all United States locations, modeling sea state for every NOAA
buoy, many Canadian and European buoys and a good collection
of virtual buoys outside these locations including Europe, Brazil
and the West Pacific.
Tell
me more about the models and their association with buoy forecasts.
Building accurate automated surf forecasts is very dependent
upon the ability of the wave model to forecast local sea conditions,
specifically those for nearshore buoys that sit within 20 nmiles
of the coast. The ability to sort out windswell from groundswell
is paramount. Since many ocean enthusiasts have built an understanding
of how real-time buoy readings correlate to near shore surf
conditions, building forecasts for those buoys to predict future
ocean and swell conditions is essential. In general, the bulletin
data gets you a forecast for an exact point, accurate to within
one tenth of a degree (about 6 nautical miles) and for 6 individual
swells hitting simultaneously. In this way the real-time NDBC
buoys become a way to verify the accuracy of the wave models.
In contrast, the best GRIB regional datasets provide one datapoint
for every .25 square degrees (one reading for every 225 square
nmiles of ocean surface) and only for the dominant 'swell'.
And the global models only have a resolution of 1 by 1.25 degrees
(one reading for every 4500 square nmiles). That's still very
good for modeling raw sea conditions, but for critical near-shore
a.cgiications, why not use the best source available? For those
locales not covered with regional bulletins, GRIB data is a
good (and the only) option. But for everywhere else, regional
bulletins are the way to go.
Which
models does Stormsurf use? As mentioned before, there
are currently 5 Wavewatch III wavemodels run in near-parallel,
all using the same initial atmospheric state data. The prime
one is the global model which provides global forecasts (with
less fidelity but more coverage area). There are 3 regional
models (West North Atlantic, East North Pacific, and the Alaskan
model) which focus on specific regions while providing greater
resolution), and two hurricane models which superimpose the
fine details of hurricane surface circulation on the regional
models providing an even higher operating resolution. Each
of these models provides bulletins for specific locations,
and with varying degrees of fidelity. These models are the
state of the art in predicting conditions on the oceans surface
and generally quite accurate. Stormsurf uses bulletin data
from the highest fidelity models, the regional and hurricane
models, whenever possible to provide the highest level of
accuracy and fidelity.
Note
of Caution: Though the models are state of the art
and a tremendous leap forward in wave modeling technology,
that does not mean they are infallible. The reality is that
there are still physical process in the real world that that
are not well understood and constructed in the theoretical
world. One has to develop some skill using these models (for
several years) to get a good feel for their strengths and
weaknesses. The further out the forecast goes, the less accurate
it is. But the near-term projections (one to 2 days out) are
normally pretty good. Remember, the data you are viewing is
raw data. Use it as a rough guile only. Manually computed
groundswell forecasts still have the edge in accuracy.
How
often are the forecasts updated? The models at NOAA
are run once ever 6 hours (4 times per day). Stormsurf downloads
the data right after it's posted by NOAA, and processes it
for presentation on our site. The fresh data is loaded real-time
for viewing. The date and time from the source files (model
run time) are posted on each page.
How
is this data prepared for presentation? Each site
specific bulletin is parsed using Stormsurf's custom designed
proprietary algorithms that determine the two largest swells
(of up to 6 that are documented at each site). The 'top two'
are selected using the combination of swell height and period
that will produce the largest waves.
Why
only the 'top two' swells? We could have done the
top three or four swells, but two seems to be the most that
a person would ever notice at one location at a time. Also
the pages would get too large to view. As is common in many
locations, it is possible to have one ground swell coming
from say the south, and another from the north. Or a combination
of windswell and groundswell coming from the same direction
but with different periods. From a surfing perspective, the
groundswell is usually the swell most sought after because
of it's concentration of power and energy. The top two seems
to account for most normal conditions around the globe.
Surf
Height from Primary or Secondary Swells: This graph
depicts the height of waves that will result when the primary
or secondary swell breaks at beaches nearest the buoy. We calculate
the surf height using a combination of swell height and period
and scale the result using proprietary tables that account for
the buoys proximity to land. The surf height estimates are a.cgiicable
only to those breaks relatively close to the buoy. As you move
to beaches further away from the buoy, the accuracy falls off.
But in such cases, normally, there are other buoys to select
from.
Surf
Height is not specific to any particular break. It
represents the size of the average set wave at a theoretical
break that has neither anything to reduce the size of the swell
or enhance it. Bathymetry can significantly alter the resulting
wave size. Waves can be as much as twice the stated size or
down to one half the stated size. Things that can reduce swell
size include (but are not limited to) obstructions that prevent
a swell from proceeding straight towards the beach, like islands,
points or anything that causes the swell to wrap or change direction.
Offshore shoals, reefs or sandbars can cause the swell to drag
on the bottom and loose energy, reducing size too. Conversely,
certain ocean bottom configurations enhance wave size like:
deep water trenches that deposit a swell onto a shallow reef
or jetties than cause reflections (to name two). In short, use
this data in combination with your local knowledge of the breaks
near where you surf to determine what location will be best
suited for your skills.
Primary
and Secondary Swell Height and Period: This is the
forecast height and period of the Primary and Secondary Swells.
Height is in feet and period is in seconds, the same as what
is normally reported at the NOAA buoys. Remember, smaller swells
with longer periods often result in larger waves than seemingly
bigger waves that have short periods.
Combined
Sea Height (also known as Significant Seas): This
is the summation of all the energy expected to be hitting
the buoy. It is a rough approximation of the height of the
highest 1/3 of all waves that passed under the buoy. Individual
swells up to twice this size could occur once every hour.
Note that combined Sea Height does not necessarily correlate
well to near-shore surf height. Chop and short period windswell
can skew the numbers to the high side. That's why we tend
to dow.cgiay this graph, and provide it as a rough guide only.
Surf
Height Variability: This graph depicts the variability
of surf height caused by the interaction of groundswell and
windswell. The more windswell there is, the greater the variability.
This data is calculated by first computing the surf height
for the primary swell. Next we calculate the surf height for
combined seas using the primary swell period as dominant period
for the seas (E.g. if swell was 6 ft @ 17 secs and seas were
8 ft, then the input range would be 6-8 ft @ 17 secs). The
graph should not be taken too literally, but is provided mainly
as a rough guide to help set expectations.
