Surf Discussion
Issued by NWS Honolulu, HI

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FXHW52 PHFO 240102
SRDHFO

Collaborative Nearshore Swell and Wind Forecast for Oahu
NWS/NCEI Honolulu HI
302 PM HST Fri Oct 23 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        2   NW    8     1     2  SAME          7-10     S   SAME
10/23       3  ENE    7     1     2  SAME
            2  SSE    9     1     2  SAME

SAT         2   NW   18     4     6    UP   LOW    7-10    SE   SAME
10/24       4  ENE    8     2     3    UP   LOW
            2  SSE    9     1     2  SAME   LOW

SUN         7  NNW   14    12    16    UP   LOW    9-13   ESE     UP
10/25       5  ENE    8     3     5  SAME   LOW
            2    S   11     1     3  SAME

MON         6  NNW   13     8    12  DOWN   LOW    9-13   ESE   SAME
10/26       5  ENE    7     2     4  DOWN   LOW
            2   NE   12     2     4    UP   LOW
            2  SSE    9     1     2  SAME   LOW

TUE         5  NNW   12     6    10  DOWN   LOW    9-13     S   SAME
10/27       3   NE   11     3     5  SAME   LOW
            1  SSW   15     1     3    UP   LOW

WED         3  NNW   11     4     6  DOWN   LOW    9-13   ESE   SAME
10/28       3   NE   11     3     5  SAME   LOW
            1  SSW   14     1     3  SAME   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....Active surf from NW to NNW by Sunday.

DETAILED...
Mid Friday on northern shores has breakers at a seasonal minimum.
Similar low surf is expected to hold into Saturday PM.

See the latest NWS State Forecast Discussion for trends in local
winds and skies. Wind estimates in table above are open for updates
given the unsettled weather pattern in the vicinity this period.

A favorable pattern for above average surf in Hawaii unfolded in the
NW to central N Pacific 10/20-23. It should make for a long-lived
event beginning late Saturday.

A compact, gale, low-pressure cell near 45N, 175E late 10/20 moved
ESE to 175W 10/21 as it strengthened. The system became occluded by
late 10/21 which coincides with a slowing of the track, a broadening
of the circulation gyre, and a strengthening of the surface winds.
The pattern has remained fairly stationary 10/22-23 with a slight N
shift of the center. It is expected to weaken sharply 10/24.

The initial gales over the 315-330 degree band increased to within
severe gales to storm-force winds after the occlusion late 10/21 into
10/22 as the fetch favored 320-335 degrees. The head of the fetch
reached near 40N, 175W or about 1500 nm away 10/22 PM. JASON
altimeter 00Z 23 OCT, or 2 PM HST Thursday, showed combined seas and
swell above 20 feet near 40N, 175W, higher than modelled by the Wave
Watch III. The long, wide fetch held the same into mid Friday 10/23
though winds have steadily dropped toward the marginal gale bracket
over the 320-335 degree band over the last 18 hours.

Long-period forerunners are due locally near sundown Saturday from
315-330 degrees. The event should be above the October average by
dawn Sunday 10/25. The event should peak mid Sunday centered from 325
degrees. Heights should slowly decline to near the October average by
Tuesday 10/27 from the same direction. The event should linger at
small levels 10/28 and fade 10/29.

Mid Friday on eastern shores has breakers at an east side minimum.
Similar surf is predicted Saturday AM with a slight increase Saturday
PM.

Surface high pressure near 1030 mb near 40N, 140W became established
10/22 and is modelled to hold about the same into 10/26. ASCAT
satellite Friday morning 10/23 shows fresh breezes with pockets to
strong beyond about 300 nm away from away from Oahu to the E to NE.
Short-period waves of 6-8 seconds are predicted to increase Saturday
PM from 50-90 degrees, making for small breakers. It should trend up
to near the average by Sunday 10/24 and hold into Monday as the event
decreases. A new remote wind swell is due at this time.

A similar situation to a week ago has set up off California on the SE
side of the high-pressure cell. Strong to near gale winds are aiming
at targets SE of Hawaii. This should send in a remote wind swell
locally. Breakers should hold near average late Monday into Wednesday
10/26-28 from 45-70 degrees.

Mid Friday on southern shores has breakers near seasonal background
levels from 140-220 degrees. Similar surf is predicted for Saturday.

South shores of Hawaii are in transition mode as the southerly swell
season wanes. No surf beyond background is expected this period from
140-220 degrees. 2019 saw above average southerly swell into Veterans
Day weekend. There are still low odds for one to a few more S
episodes before the winter sets in, when dominant surf typically has
a W-component for peak days.

Into the long range, south side should hold at a seasonal minimum
10/29-31.

East side is modelled to trend down 40-90 degrees below average
10/29-31.

For north shores, surf is expected hold near a seasonal minimum
10/29-31, with small, shorter-period NNW to N surf.

Long range forecasts are subject to low confidence.

The next Collaborative Forecast will be updated Monday, October 26.



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 Forecaster and NCEI Pat Caldwell


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