Oahu Surf Conditions
Surf along north facing shores will be 3 to 5 feet today, lowering to 1 to 3 feet Friday.
Surf along east facing shores will be 2 to 4 feet through Friday.
Surf along south facing shores will be 2 to 4 feet today, rising to 3 to 5 feet Friday.
Surf along west facing shores will be 2 to 3 feet through Friday.
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, at the locations of the largest breakers. 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.
The SRFHFO product will change format and be expanded to more islands on or about September 10, 2020. More information at: https://www.weather.gov/hfo/statesurf2020 .
|SWL HGT||Open ocean swell height measured from trough to crestin feet located 20 nautical miles offshore|
|DMNT DIR||Dominant direction typically +/-10 degrees in 16 compasspoints|
|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 surfzone|
|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 located20 nautical miles offshore|
|WIND DIR||Wind direction in 16 compass points|
|SPD TEND||Wind speed tendency (valid values: UP/DOWN/SAME)|
DISCUSSION: SUMMARY.... Fireworks in sky and ocean to bring in the new year.
DETAILED:. Mid Wednesday on northern shores has steady, above-seasonal-average breakers spread from 12-18 seconds, dominant in the 15-17 second band, and ranging directionally from 300-340 degrees, dominant from 320 degrees. Heights are extra-large, defined by size high enough to trigger outer reefs. Heights should remain above the seasonal average Thursday morning, though sub-extra-large, then ramp up sharply midafternoon into the evening.
A broad area of winter-caliber low pressure filled the NW to central N Pacific 12/25-28, commonly referred to as the Aleutian low, which is plentiful for most days of winter to define the average surface pressure pattern. The parent low for this present event sent extra-long-period energy to Hawaii from hurricane-force winds west of the Date Line beyond 1800 nm that took surf above average locally Monday night into Tuesday from 305-325 degrees. An offspring low added a new fetch of upper gales nosing seas to near 25 feet about 1000 nm away by 12/28. Surf from this closer source filled in overnight Tuesday and is peaking Wednesday 12/30 on Oahu. This event should slowly trend down in the wee hours Thursday to midday, though remain above average from 300-340 degrees. A larger event is imminent in the PM.
The next offspring in this extra-tropical cyclone family formed near 35N, 160E 12/28, raced ENE and reached the Date Line early Tuesday with hurricane-force winds. The track then turned more NE as it continued to deepen to 960 mb, reaching near 42N, 168W early Wednesday. The reduction in surf potential due to the fast track was well offset by the extreme winds acting upon existing high swell over the 310-330 degree band. Largest seas to 40 feet 12/30 are aimed NE of Hawaii, though 12/30 morning JASON satellite registered seas of 32-36 feet with a more direct aim at Hawaii in an area about 1000 nm away. Given the wave travel decay rule of thumb of half of the height reduced for each 1000 nm travel, that places deep water swell off Oahu late Thursday of long periods of 15-19 seconds, that would manifest at the peak of the event to giant levels, defined by the common larger, though less frequent, sets surpassing 40 feet on outer reefs in zones of high refraction. With a close source, events typically rise and fall faster, with the extreme heights likely centered overnight Thursday as the New Year rings in. It should be from 310-340 degrees, though dominant near 325-330 degrees. Heights should slowly settle down Friday though remain extra-large through the day. Heights should fall sharply Saturday to levels below the seasonal average by the afternoon from 310-360 degrees. Remnant shorter-period surf is expected for Sunday morning as a new event slowly fills in.
Keep abreast to National Weather Service updates 12/31 for fine-tuning of the timing and magnitude of the potential, short-lived, giant episode as the swell trains roll under the NOAA NW Hawaii buoys. Note the NWS statement regarding the coinciding spring high tide and upper-level winter surf, giving way to potentially well-above average coastal wave run-up 1/1 in the wee hours to near dawn.
The parent low aforementioned weakened in the Bering Sea 12/28-29. A new parent low is modelled to replace it by 12/31 over the western Aleutians with the center of low pressure dropping to near 928 mb Thursday. Hurricane-force winds about 2400 nm away should send low, extra-long-period forerunners arriving in Hawaii Saturday evening from 320 degrees. The primary event is expected to be generated by a long, wide fetch of gales to storm-force winds beyond 1800 nm away 12/31-1/1. This event should have a slow rise Sunday reaching levels above average midday from 300-325 degrees.
Models show the jet south of the parent low becoming zonal 1/1-3, and sending a new offspring of gales on a track from the far NW Pacific to east of the Date Line by 1/2. This closer source should bring larger surf, with heights growing above average early Monday and peaking late Monday from 310-330 degrees.
Mid Wednesday on eastern shores has above average surf from the trade wind belt of 70-90 degrees. Heights should be similar on Thursday.
See the latest NWS State Forecast Discussion regarding the trend in local winds and skies.
Surface high pressure has held between Hawaii and California since last weekend with a large fetch of fresh to strong breezes, and pockets to severe gales, east of Hawaii mostly within 135-150W. This upstream source has the PacIOOS/CDIP Hilo, Hawaii and Mokapu, east Oahu, buoys holding 7-10 second wave period energy, which is on the longer side of the wind swell spectrum. Longer wave periods allow more height transformation upon shoaling, and leads to more active surf. This upstream source should hold through Thursday, as a new fresh to strong trade event locally of 12/31-1/2 maintains the above average breaker heights under rough conditions from 70-90 degrees into the weekend. Heights are modelled to slowly trend down 1/3-4 to near average.
Mid Wednesday on southern shores has breakers near nil as common in winter. More of the same is likely on Thursday.
Austral summer mode became established last week into this week in the midlatitudes for longitudes from Tasmania to south of French Polynesia, which spells more of the same nil-ness locally. From late December to early March, odds are higher for surf on south shores from east or west than from south.
Into the long range, wind swell from the trade wind belt should drop below average out of 70-90 degrees by late Monday and hold below average into Wednesday 1/4-6.
The north side should hold above average 1/5 and slowly trend down into 1/7 from 310-340 degrees. Long range forecasts are subject to low confidence.
This is the last Collaborative Forecast. Thanks for support from the NWS HNL team and kind words received from the public.
This forecast was produced through the collaborative efforts of NWS and NCEI. Please send suggestions to firstname.lastname@example.org or call the Warning Coordination Meteorologist at 808-973-5275.
ADDITIONAL RESOURCES: See https://www.weather.gov/hfo/marine