Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
231 FXHW60 PHFO 191321 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 320 AM HST Wed Jun 19 2024 .SYNOPSIS... Persistent high pressure far north of the islands will support locally strong trade winds through the weekend. Brief and passing showers will favor windward areas, especially during nights and mornings, with a few sprinkles occasionally spreading leeward. && .DISCUSSION... Seasonable trade wind weather will prevail, with wind speeds slightly stronger than normal. Surface high pressure centered well NNE of the islands will strengthen slightly and drift W the next couple of days, supporting a gradually increasing trend in wind speeds, with locally windy conditions developing by the weekend. Morning soundings showed a very strong (15 degrees F at PHLI) subsidence inversion based around 6-7 kft, PWAT just above June norms near 1.4", and modest instability aloft associated with a mid- and upper-level low centered W of Kauai. VIIRS Day/Night band and traditional infrared satellite images indicate that the incoming low cloud field has become overcast and increasingly stable overnight, with radar detecting a few light showers embedded. Scattered high clouds are seen moving N over the area. The mid- and upper-level low will drift W the next couple of days, allowing a mid-level warm pool to move over the islands from the E, but periods of patchy high clouds are expected to continue. Just a few showers are expected today into Thursday, with low cloud and shower coverage likely following a diurnal pattern - with coverage greatest during nights and mornings. Increased PWAT moving over the islands from the E is expected to lead to increased low clouds and light windward showers Friday and Saturday, despite strong stability in place. This moisture is associated with a weak front currently near 27N-30N between 140W and 148W. The summer solstice will occur at 1051 AM HST Friday June 20th, marking the astronomical start of summer. && .AVIATION... Trades will gradually strengthen to become breezy to locally windy today, with showers and low cigs favoring windward and mauka locations. Periods of MVFR conditions are possible in any showers, which are expected to increase slightly in coverage during the late night to early morning hours. Otherwise, VFR conditions should prevail. AIRMET Tango is in effect for low level turbulence lee of mountains due to the strengthening trade winds. AIRMET Sierra is in effect for windward sections of the Big Island through this morning. && .MARINE... A high pressure system north-northeast of Hawaii will strengthen over the next two days, keeping fresh to strong trade winds in the forecast for most areas, and near gale-force winds over some of the windier eastern channels. A Small Craft Advisory (SCA) remains in effect for most waters around the Big Island and Maui County. Trade winds will increase into the breezy to windy range, as the high center shifts more north of the islands on Thursday and Friday. The SCA will expand in coverage over all coastal waters from Thursday into early next week. Expect diminished south shore surf through Friday. A mix of small, long period south and southwest swells may push surf heights up near seasonal averages this weekend. Another small long period south- southwest swell is expected to fill in early next week. Surf along east facing shores will gradually trend up Thursday on through the weekend as trade wind speeds strengthen by Thursday. Surf along north facing shores will return to seasonally tiny levels. Additional very small background pulses are possible Thursday and again early next week. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Thursday for Kaiwi Channel- Maui County Windward Waters-Maalaea Bay-Pailolo Channel- Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Birchard AVIATION...Farris MARINE...Bohlin