FXHW52 PHFO 101749 CCA SRDHFO Collaborative Nearshore Swell and Wind Forecast for Oahu NWS/NCEI Honolulu HI 242 PM HST Mon Nov 9 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 NNE 11 3 4 DOWN 17-21 E UP 11/09 7 E 9 5 7 UP TUE 9 E 9 6 8 SAME MED 17-21 ENE SAME 11/10 2 NW 13 2 4 UP LOW 1 SSW 15 1 3 UP WED 10 ENE 9 7 9 UP MED 22-27 ENE UP 11/11 2 NNW 11 2 3 DOWN LOW 1 SSW 14 1 3 SAME LOW THU 10 ENE 9 7 9 DOWN LOW 19-23 ENE DOWN 11/12 FRI 8 ENE 8 5 7 DOWN LOW 17-21 ENE SAME 11/13 2 NNW 17 4 6 UP LOW 1 SSW 17 2 4 UP LOW SAT 7 ENE 7 4 5 DOWN LOW 12-18 ENE DOWN 11/14 5 NNW 14 8 10 SAME LOW 2 SSW 14 2 4 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.... Rough trade wind swell through the work week topping the heights. NNW surf due for the weekend. DETAILED... Mid Monday on eastern shores has declining short- to moderate-period surf from 020-060 degrees and rising, rough, short-period breakers from 60-90 degrees. The combination places surf above the east side average 11/09. Conditions are expected to remain rough with above average breakers on Tuesday favoring 60-90 degrees. A surface high pressure cell to 1045 mb was established 11/6 near 45N, 150W to the NNE of Hawaii. The fetch over the 000-040 degree band beyond 1000 nm out began to weaken 11/7. Surf from this source kept active breakers for more northerly exposures Sunday into Monday morning, when moderate breakers held on. By midday Monday 11/09, surf has dropped sharply as this source fades away and dominant shorter-period swell favors ENE to E. A large jet-level ridge and its associated strong surface high pressure fill the NE Pacific to the NE of Hawaii 11/09. ASCAT satellite since 11/8 shows a wide, long fetch of fresh to strong trades from near Hawaii E to NE out over 1000 nm. Models show the ridge and surface high moving west to a position north of Hawaii by late Tuesday, then holding strong into Thursday. This should make for an extended period for rough, above average breakers from trade wind swell out of 60-90 degrees. Models show a westward-moving, upper level trough immediately east of Hawaii 11/12 that would weaken the surface pressure gradient, thus the speed of the upstream trades. This upper-level feature is predicted in the vicinity 11/13-14. This pattern should lead to a downward trend 11/13-14 in local, short-period breakers from 60-90 degrees. See the latest NWS State Forecast Discussion regarding the influence of this upper-level feature on the trend in local winds and skies late in the week. Mid Friday on northern shores has breakers from 20-40 degrees well below the seasonal average. There has been a steep drop in size Monday morning aforementioned. Heights are expected to remain near low on Tuesday more from the NW. Gales east of the Kuril Islands 11/5 aimed swell toward Hawaii beyond 2200 nm away, that got a minor extra push from near gales associated with a low pressure NW of Hawaii 11/7-8. The combined low swell should fill in locally overnight from 305-330 degrees 11/09. This small event should peak late Tuesday 11/10 and drop into Wednesday. Models show a stronger gale racing east along 50N reaching the Date Line late Tuesday with seas to 25 feet. This source has better odds for surf locally with the source closer. Models suggest long-period forerunners from 310-325 degrees Friday PM with the event peaking Saturday from 315-335 degrees, likely a notch under the fall season average. It should be short-lived. Mid Friday on southern shores has breakers at a seasonal minimum. Low surf is predicted to continue on Tuesday with a slight increase. Exposures to east wind swell on the south side should trend this period aforementioned. A fast-moving gale in the high latitudes S to SE of New Zealand 11/2-3 could bring a low, long-period event building 11/10 and dropping 11/11 from 180-200 degrees. A slightly broader and stronger system SE of New Zealand 11/5-6 could do similar locally 11/13-14. Into the long range, peak days from the south at most background levels within 11/15-17. Models show east side trending down below average 11/15-16 from 60- 90 degrees. Models show a jet-level trough and surface low in the Gulf of Alaska 11/14-16, that could bring N to NE surf near the average roughly 11/17-18. Long range forecasts are subject to low confidence. The next Collaborative Forecast will be updated Friday, November 13. 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