Atmospheric Model: Using a 'snapshot' of actual
current atmospheric conditions as input, mathematical computations are executed on a
computer to simulate the evolution of weather conditions for periods ranging from several
hours to weeks or more into the future. In general, models are good for determining the
probability of mid to large scale weather events. Models are very CPU intensive and
therefore, costly to run.
AVN, MRF, NGP, ETA, RUC, MM-5: Standard mathematical atmospheric models
used to project what the weather will be for a specific geographic location for some
period of time in the future. Typically each model forecasts pressure, temperature, wind
speed and heading at various heights in the atmosphere, and relative humidity and
precipitation amounts. Generally, short-term forecast models (72 hr or less) run at higher
fidelity. For practical purposes, models that forecast in excess of 4-5 days are only good
for indicating tendencies in the weather pattern, and cannot be used to identify specific
local weather occurrences. Each model is fine-tuned to support particular needs.
AVN (Aviation) 3 day model in 12 hr
MRF (Medium Range Forecast) up to 9 day model in 12 hr
NGP (NoGaps) similar to the MRF
ETA 48 hr model in 12 hr increments
RUC 12 hr model in 3 hr increments
MM-5 scalable to cover very small geographic locations with
a higher degree of resolution/fidelity.
ENSO: El Nino Southern Oscillation. This term is
synonymous with the El Nino/La Nina cyclical pattern. El Nino statistically enhances
consistency and size of northwest Pacific winter storms, thereby increasing the
probability of larger and more consistent winter surf. La Nina conditions tend to have the
ERS-2: European Remote Sensing Satellite. This is a
polar orbiting satellite that has sensors which are used to measure wind speed, wind
direction and sea heights accurate to within about 4 centimeters. The satellite passes
over the entire surface of the earth once every 18 hours, but doesn't cover every square
meter, only thin bands (about 50-100 miles wide). This is an excellent source for
confirming wind speeds and seas heights in locations where buoys are not present (like the
North Pacific on the dateline). Raw ERS-2 data must be interpreted by computer and the
results are available for review roughly once every 12 hours at select Web sites.
Ft: Feet, a measure of height or amplitude.
Kts: Knots or 'nautical miles per hour' is a measure
of speed or velocity.. A nautical mile is about 1.15 times the distance of a standard
statute mile. So, wind which blows at 69 kts is equivalent to 77 mph (69kts X 1.15 =
Mb or mbs: millibars. An increment for
measuring barometric/air pressure. Typically used to identify the strength of a low or
high pressure weather system. Most home barometers use "inches" rather than
millibars. The lower the mb number, the deeper the low pressure system. The higher the mb
number, the stronger the high pressure system is. 950 mb is a very strong/intense low
pressure system. 1028 mb is a fairly strong high pressure system. Normal surface pressure
is about 1000 mbs.
Mon - Sun: Abbreviations for days of the week
nmiles: Nautical miles is a measure of distance. A nautical mile is about
1.15 times the distance of a standard statute mile. For swell prediction purposes, it is
used to determine swell arrival time. A swells period (in secs) can be translated into
swell speed (in kts). Roughly, swell period times 1.5 equals swell speed in Kts. If you
know how far away a swell producing storm is from your location (in nmiles), and you can
estimate the swells average period, you can determine the number of hours till the swell
arrives at your shore.
Sec or Secs: Seconds. Typically used in combination with the term 'Ft' to
identify the height and period of a swell/sea. Example 14 ft @ 14 sec = 14 feet at 14
seconds. Reference output of any buoy.
SOI Index: A numeric value assigned to the difference
in surface pressure between Darwin,Australia and Fiji. A negative SOI index number is
indicative of El Nino conditions, while positive values indicate La Nina.
SSM/I: There is an polar orbiting F-8 satellite
equipped with a Special Sensor Microwave/Imager(SSM/I) device that measures wind speed (no
direction). It covers every square inch of the earth's surface every 18 hours.
WAM : Short for Wave Model. These models
predict significant sea heights and main swell direction/vector up to 9 days in the
future. NOAA and FNMOC have operational wave models available on the Web. The NOAA
model is driven using the AVN atmospheric model (and is limited to 72 hr forecast period)
while the FNMOC uses the NGP atmospheric model (and can predict up to 9 days ahead). In
general, wave models are not a good source for developing a surf forecast. But, they are
quite good for determining the probability for future swell generation potential. Only
confirmed ERS-2/SSMI outputs yield reliable swell prediction results.
All storms that appear capable of producing 'significant
swells' will be numbered. The resulting swell will be numbered also to correspond with the
storm number (i.e. 'Storm 5' produces 'Swell 5'). In this way, a total count of
significant storms and swells can be determined for the season, and when multiple storms
occur simultaneously, each resulting swell can be uniquely identified (like tracking
hurricanes by using 'names'). The first swell of the winter season will be Swell 1
Example: Swell 1 (1997/98)
Summer (June through August)
In summer, Southern Hemisphere and swells of tropical origin
will be numbered when they appear to be significant, that is, when the resulting swell
size is estimated to be equal or greater than 3 ft @ 17 secs. The numbering convention
will be like the winter numbering scheme, except an 'S' will be appended to the number
Example: Swell 1S (1998)
Please see the paper titled Swell Rating System for all the
details concerning Swell Categories.
Impulse Swell: A Category 1
swell with a period of 17 secs or greater. (Waist to head high)
Utility Swell: All Category 2
or 3 swells (Head high to just under double overhead/4.5 ft overhead)
Signficant Swell: All
Category 4-7 swells (double overhead to 5 times overhead plus!)