Pat Caldwell

Outlook
Outlook through Monday April 27: surf heights will remain at advisory levels over east facing shores through early Wednesday. A south swell will reach near advisory levels today and remain so until Thursday, then gradually subside through the rest of the week. Another reinforcing small northwest swell will peak tonight then gradually diminish through the rest of the week. Surf heights are forecast heights of the face or front of waves. The surf forecast is based on the significant wave height, the average height of the one third largest waves, in the zone of maximum refraction. Some waves may be more than twice as high as the significant wave height. Expect to encounter rip currents in or near any surf zone.
Hazards
HIGH SURF ADVISORY FOR EAST FACING SHORES
Forecast
Surf along north facing shores will be 5 to 7 feet today, decreasing to 4 to 6 feet Wednesday. Surf along west facing shores will be to 3 to 5 feet today, decreasing to 2 to 4 feet Wednesday. Surf along east facing shores will be 6 to 10 feet through Wednesday. Surf along south facing shores will be 5 to 7 feet through Wednesday.
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About Collaborative Surf
This collaborative forecast will be updated Monday through Friday at 300 pm when Pat Caldwell is available.
Collaborative Surf Discussion
SURF HEIGHTS WILL VARY BETWEEN DIFFERENT BEACHES AND AT THE SAME BEACH AT DIFFERENT BREAK AREAS. DISCUSSION: Summary: spring surf from around the compass. Detailed: mid Monday on northern shores has breakers near the late April - early may average from 330-350 degrees with 10-12 second intervals. An increase is expected on Tuesday. Two low pressures cells merged near the Aleutians east of the dateline on Friday. The initial stages produced the local NNW surf for 4/19-20. The combined system broadened 4/17-18 with strong to near gale breezes covering a long, wide fetch from near the dateline on the Aleutians to near 40°N, 165°W. The system moved east of the Hawaii swell window on 4/19. Based on seas of 10-12 feet about 1000 nm away on Sunday, this should give swell near 4 feet locally. It should trend up on Tuesday from 325-345 degrees, peak late Tuesday, and drop on Wednesday. Tiny to small remnants are possible on Thursday. A weak low pressure formed east of Japan on 4/18 and has reached the dateline near 40°N on 4/20. Winds were sub-gale over the 300-315 degree band 4/19. Models show the system occluding as it stalls on Tuesday, with weaker winds aimed at Hawaii. Only a tiny to small, short-period WNW episode is expected Friday into Saturday, lower than the refracting easterly windswell that should be steady through the week. Mid Monday on eastern shores has rough, above trade windswell average breakers from 60-90 degrees with 6-10 second periods. Similar conditions are expected on Tuesday. See the latest NWS state forecast discussion regarding the local wind and weather trends. Surface high pressure north of Hawaii 4/20 is modelled to move NE, then remain stationary between Hawaii and California into the weekend. This should keep the rough seas to the immediate E to ENE of Oahu stretching out over 1000 nm. This type pattern makes for above trade windswell average breakers. It should remain active into Friday, with a downward trend on Saturday. Mid Monday on southern shores has long-period southerly swell with a rising trend. Heights are near the summer average, meaning refractive spots on the common, though less frequent higher sets around 5 feet peak face. It is a mix of Tasman sea energy from 208-220 degrees with 14-15 second periods and New Zealand energy out of 190-200 degrees with 16-19 second period. The latter should dominate on Tuesday with a continued rising trend. Low pressure over New Zealand 4/11-12 placed gales in the Tasman sea. Swell from this source out of 208-220 degrees picked up locally Sunday 4/19. It should linger on Tuesday. The low pressure area moved east 4/13-14 as a secondary low pressure cell from S of New Zealand merged into it, dropping central pressure to 955 mb near 50s, 170°W 4/14. A long, wide fetch of gales to severe gales grew seas to 30 feet with the head of the fetch about 3800 nm away. The system weakened as it moved slowly ENE 4/15-18. The pacioos/cdip american samoa buoy showed a sharp rise in swell height 4/17. It remained elevated with a secondary maximum early on 4/19. Dominant periods were around 15 seconds through the period. With the 2200 nm travel distance and swell centered on 190 degrees, this would take 4 days to reach Hawaii. Surf is expected to slowly increase late Monday through Tuesday, then remain at a quasi-maximum late Tuesday to early Thursday from 180-200 degrees at levels above the summer average. Heights should fall to near the summer average on Friday then gradually fall to summer background levels over the weekend from the same direction. Into the long range, the near gale remnant of the New Zealand low remained active SW to SE of Tahiti 4/17-19. It should keep shorter-period background level surf from 170-180 degrees Sunday into next Tuesday 4/26-28. A more zonal jet stream set up for longitudes from Tasmania to French Polynesia 4/16-20 within 50-70s and is expected to hold this week. This would mean below average surf locally with off and on, background level long-period swell out of 180-220 degrees 4/26-30. In the northern hemisphere, models track a gale low in the Bering Sea from near Kamchatka 4/21 to the dateline 4/23. It is expected to place marginal gales hugging the Pacific south of the Aleutians. It could bring in NNW surf near the late April average locally late Sunday 4/26, peaking Monday 4/27, and slowly dropping 4/28-29 from NNW to N. Models suggest easterly windswell to be near or a notch above the trade windswell average 4/26-28. Long range forecasts are subject to high uncertainty. This collaborative forecast will resume on Wednesday, April 22. This forecast was produced through the collaborative efforts of NWS and NCDDC. Please send suggestions to w-hfo.webmaster@noaa.gov or call the Warning Coordination Meteorologist at 808-973-5275. Additional resources: see /in lowercase/ http://www.prh.noaa.gov/hnl/pages/marine.php.
Collaborative Surf Table
FORECAST
DATE
SWL
HGT
DMNT
DIR
DMNT
PD
H
1/3
H
1/10
HGT
TEND

PROB
WIND
SPD
WIND
DIR
SPD
TEND
1PM
04/20
3NNW1146SAME19-23ENESAME
8ENE9610SAME
2SW1424DOWN
2SSW1736UP
TUE
04/21
4NNW1268UPMED19-23ESAME
8ENE9610SAMEMED
4SSW1568UPMED
WED
04/22
3NNW1146DOWNLOW17-21ESEDOWN
7E958DOWNLOW
4SSW1568SAMEMED
THU
04/23
2NNW923DOWNLOW17-21ESESAME
7E958SAMELOW
4SSW1468DOWNLOW
FRI
04/24
2WNW1123UPLOW17-21ESESAME
7E958SAMELOW
3SSW1346DOWNLOW
SAT
04/25
2WNW1023SAMELOW13-19ESEDOWN
6E947DOWNLOW
2S1325SAMELOW
Disclaimer
Collaborative Surf Table Legend

LEGEND:

SWL HGTOPEN OCEAN SWELL HEIGHT MEASURED FROM TROUGH TO CREST IN FEET LOCATED 20 NAUTICAL MILES OFFSHORE
DMNT DIRDOMINANT DIRECTION TYPICALLY +/-10 DEGREES IN 16 COMPASS POINTS
DMNT PDDOMINANT PERIOD IN SECONDS
H1/3SIGNIFICANT WAVE HEIGHT IN THE SURF ZONE
H1/10AVERAGE HEIGHT OF THE HIGHEST ONE-TENTH WAVES IN THE SURF ZONE
HGT TENDHEIGHT TENDENCY OF SWELL (VALID VALUES: UP/DOWN/SAME)
PROBPROBABILITY OF OCCURRENCE (VALID VALUES: HIGH/MED/LOW)
WIND SPDOPEN WATER WIND SPEED MEASURED IN KNOTS LOCATED 20 NAUTICAL MILES OFFSHORE
WIND DIRWIND DIRECTION IN 16 COMPASS POINTS
SPD TENDWIND SPEED TENDENCY (VALID VALUES: UP/DOWN/SAME)
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NWS FORECASTER AND NCDDC PAT CALDWELL

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