528 FXHW52 PHFO 130030 SRDHFO Collaborative Nearshore Swell and Wind Forecast for Oahu NWS/NCEI Honolulu HI 230 PM HST Fri Apr 12 2019 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 WNW 12 2 4 SAME 19-23 ENE SAME 04/12 2 NNW 14 2 4 UP 11 E 11 8 12 UP SAT 3 WNW 12 4 6 UP LOW 19-23 ENE SAME 04/13 3 NNW 13 4 6 DOWN LOW 11 ENE 11 8 12 SAME LOW SUN 2 NW 11 2 4 DOWN LOW 17-21 ENE DOWN 04/14 10 ENE 11 8 10 DOWN LOW MON 5 WNW 16 8 12 UP LOW 11-16 ENE DOWN 04/15 8 ENE 9 6 8 DOWN LOW TUE 4 NW 14 6 8 DOWN LOW 7-10 E DOWN 04/16 5 ENE 8 4 6 DOWN LOW WED 3 NNW 11 4 6 DOWN LOW 9-13 E UP 04/17 4 ENE 8 2 4 DOWN 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 from WNW to NNW for north shores and rough, large ENE to E windswell for eastern exposures. DETAILED... Mid Friday on northern shores has tiny to small breakers from 305-360 degrees. An increase is due late Friday. Shorter-period swell from 285-310 degrees were generated west of the Date Line 4/8-10. This weak event is filling in Friday, should peak on Saturday, then fade out Sunday. Moderate-period swell is rising mid day at NOAA buoy 51001 NW of Kauai and the Hanalei, Kauai PacIOOS/CDIP site with 13-15 second energy. It was generated by a fast-moving, hurricane-force system that crossed the Date Line 4/10 heading to the Aleutians with highest seas aimed well NE of Hawaii. This short-lived event should peak Friday night from 315-330 degrees then slowly drop into Sunday. A compact, storm-force system formed east of Tokyo 4/11. It has tracked NE and was near 40N, 170E early 4/12 with seas growing near 30 feet. Models show it crossing the Date Line near the Aleutians early Saturday as the system weakens and aims more west to east well NE of Hawaii. Long-period forerunners are due locally Sunday night from 300-315 degrees. The event should build near to a notch above the April average by Monday PM from 305-320 degrees, peak Monday night, then slow drop into Wednesday from 310-330 degrees. Mid Friday on eastern shores has rough breakers from 60-90 degrees at levels well above the trade windswell average. Similar conditions are predicted for Saturday. Surface high pressure of 1040 mb near 40N, 140W 4/10-11 set up a large fetch of strong trades within 20-30N, 130-150W. The high is slowly weakening as it shifts WSW 4/12. ASCAT satellite Friday morning shows a drop in the strength of the wind over that same area mostly in the fresh to strong bracket. The seas generated 4/10-11, added with the locally strong trades, should keep surf about the same into Saturday from 60-90 degrees. Local winds and seas are predicted to slowly subside Sunday into Monday while breakers remain above average with a similar downward trend. A jet stream level trough and associated surface front are modelled to move from west to east north of Hawaii Tuesday into Wednesday, bringing trades down to a minimum. Seas generated east of Hawaii into Sunday 4/14 should keep breakers near the average Tuesday 4/16 with heights falling below average Wednesday 4/17 from 60-90 degrees. Mid Friday on southern shores has rising short-period breakers from the local trade wind event aforementioned. Similar breakers for easterly exposures of the south shore are expected for Saturday. The Tasman Sea 4/6-8 had gales that would likely be the dominant background swell locally 4/15-17. Into the long range, broad marginal gales tracking east along 65S to the S of New Zealand 4/11-13 and a compact gale east of New Zealand 4/11-12 could shift the background swell locally to 180-210 degrees for 4/19-21. The long-lived jet stream ridge over and SE of New Zealand, that has led to a below average start of the south swell season, is modelled to give way to a long- wave trough starting 4/14-18. A the surface a broad, comples area of low pressure systems 30-70S within 150-180W should have a direct aim of seas and swell at Hawaii. This suggests surf climbing to the average with peak days above average within 4/22-26. In the north Pacific, models show near gales behind a SE-pushing front from the Date Line at the Aleutians 4/14 to 1000 nm away from Hawaii 4/16 that should bring a shorter-period NNW event locally 4/19-20 at levels a notch under the April average. Models depict trade winds increasing 4/19-21 with breakers from windswell out of 60-90 degrees climbing to near the average. Long range forecasts are subject to high uncertainty. This collaborative forecast will resume on Monday April 15. 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 http://www.prh.noaa.gov/hnl/pages/marine.php $$ NWS Forecaster and NCEI Pat Caldwell