Surf Discussion
Issued by NWS Honolulu, HI

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FXHW52 PHFO 220012
SRDHFO

Collaborative Nearshore Swell and Wind Forecast for Oahu
NWS/NCEI Honolulu HI
212 PM HST Fri Feb 21 2020

This collaborative forecast will be updated Monday through Friday at
300 PM when Pat Caldwell is available.

FORECAST  SWL  DMNT DMNT  H    H     HGT          WIND   WIND   SPD
DATE      HGT  DIR  PD    1/3  1/10  TEND   PROB  SPD    DIR    TEND

1 PM        3  NNW   12     4     6  DOWN         19-23   E     SAME
02/21       9  E      9     6     8  SAME

SAT         5  NW    15     8    10  UP     MED   11-16   E     DOWN
02/22       7  E      9     5     7  DOWN   LOW

SUN         4  NNW   13     6     8  DOWN   MED     4-6   VRB   SAME
02/23       5  E      9     4     6  DOWN   LOW

MON         3  NNW   11     4     6  DOWN   LOW    9-13   NE    UP
02/24       4  E      9     3     5  DOWN   LOW

TUE        13  NNW   17    28    36  UP     LOW   13-19   ENE   UP
02/25       6  ENE    8     3     5  SAME   LOW

WED         8  NNW   14    14    18  DOWN   LOW   17-21   ENE   UP
02/26       7  ENE    8     4     6  UP     LOW

LEGEND:
SWL HGT    Open ocean swell height measured from trough to crest
           in feet located 20 nautical miles offshore
DMNT DIR   Dominant direction typically +/-10 degrees in 16 compass
           points
DMNT PD    Dominant period in seconds
H1/3       Significant wave height in the surf zone
H1/10      Average height in the highest one-tenth waves in the surf
           zone
HGT TEND   Height tendency of swell (valid values: UP/DOWN/SAME)
PROB       Probability of occurrence (valid values: HIGH/MED/LOW)
WIND SPD   Open water wind speed measured in knots located
           20 nautical miles offshore
WIND DIR   Wind direction in 16 compass points
SPD TEND   Wind speed tendency (valid values: UP/DOWN/SAME)

Surf heights will vary between different beaches and at the same
beach at different break areas.

DISCUSSION:
SUMMARY... North shores trending up while east side receives
steady windswell.

DETAILED...
Mid Friday on northern shores has breakers from 320-360 degrees at
levels below the seasonal average. An increase is predicted for
Saturday.

A zonal jet stream has held this week. Such patterns steer surface
low pressure systems rapidly east, which reduces surf potential.
The second in a pair of events is due on Saturday.

The first event generated 2/16-17 east of the Date Line is
steadily dropping 2/21. It should fade out by Saturday.

The source for the second event, due locally Saturday, formed east
of the Kuril Islands 2/17-18. It started off with severe gales
over the 300-315 degree band. The winds weakened to gales as it
crossed the Date Line 2/19 and moved east of the Hawaii swell
window 2/20.

The onset at NOAA NW Hawaii buoys 51001 and 51101 is slow relative
to the Wave Watch III prediction, which also called too early and
too high the first event aforementioned. This suggests surf
locally to build Saturday morning instead of Friday night as the
models suggest. The event should be filled in by Saturday PM from
300-330 degrees. It should peak overnight Saturday night just below
average, with a slow decline into Monday from 315-345 degrees.

Models show the central north Pacific jet stream returning to a
winter mode this weekend with a broad gyre and amplifying trough
expected to form near the Date Line Saturday. At the surface, a
severe gale low to near 980 mb is modelled to track SE into Sunday
night, bringing gales with near 25 feet seas over a captured fetch to
within 1000 nm of Hawaii. Proximity should lead to well above
average surf in Hawaii.

The onset should be rapid Tuesday near dawn with surf climbing by
mid morning from 320-340 degrees to extra-large levels, meaning
high enough for outer reefs. It is expected to peak near sundown
Tuesday 2/25. It should hold above average Wednesday 2/26 from the
same direction with a steady decline.

Mid Friday on eastern shores has rough breakers from 60-90 degrees
at levels above the trade windswell average. Heights are predicted
to remain above average on Saturday.

See the latest NWS State Forecast Discussion regarding the trend
in local skies and winds.

Surface high pressure near 35N, 150W 2/21 is modelled to slowly
shift eastward, but keep fresh to strong trades in the 60-90
degree trade wind belt aimed at Hawaii east of 155W. This should
keep active breakers locally with a slow downward trend Sunday
into Tuesday, when a new trade wind event begins.

The a new surface high pressure system is modelled to shift
eastward from the NNW to NNE of Hawaii starting 2/25. This should
lead to an upward trend in windswell mid week from 60-90 degrees.

Mid Friday on southern shores has near nil breakers. Low
conditions are expected to continue on Saturday.

Various sources in the austral mid latitudes between longitudes of
New Zealand to French Polynesia are expected to keep off and on
low, long-period swell near 1 foot in the deep ocean this period.
2/22-24 should favor from 190 degrees, and 2/25-26 from 180
degrees. This should make for inconsistent, tiny to small
breakers at high refraction zones, while most areas remain near
the winter minimum.

Into the long range, another low, long-period event is suggested
locally from 170 degrees roughly 3/1.

In the north Pacific, models show a storm-force low pressure
occluding east of the Kuril Islands 2/23-24 then slowly weakening
west of the Date Line 2/25. Wave models suggest an event near the
seasonal average from 300-320 degrees starting late 2/27 and
peaking 2/28.

Trade windswell is modelled to build above average 2/27-29.

Long range forecasts hold low confidence.

This collaborative forecast will resume on Monday, March 2.

This forecast was produced through the collaborative efforts of
NWS and NCEI. Please send suggestions to w-hfo.webmaster@noaa.gov
or call the Warning Coordination Meteorologist at 808-973-5275.

ADDITIONAL RESOURCES:
See  https://www.weather.gov/hfo/marine

$$

NWS Forecasters and NCEI Pat Caldwell


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