Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
159 FXHW60 PHFO 190658 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 858 PM HST Tue Jun 18 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 persist through the foreseeable future, with wind speeds on the higher end of the spectrum. Afternoon soundings showed a strong subsidence inversion based near 6000 feet, PWAT just above June norms at 1.35", and instability aloft (most notable above 15000 feet in the PHLI sounding), associated with a mid- and upper-level low centered just W of Kauai. Satellite data and empirical observations indicate that the incoming low cloud field is broken to overcast in coverage, and is primarily comprised of stable stratus, with a few embedded showery cumulus elements. Radar shows most of the showers over windward slopes, but light returns are seen spreading leeward on the smaller islands. Scattered mid- and high level clouds are seen moving N over the area. Surface high pressure centered well N of the islands will strengthen slightly over the next couple of days, supporting a gradually increasing trend in wind speeds, with locally windy conditions developing by the weekend. The mid- and upper-level low will drift W over the next couple of days, allowing a stabilizing mid-level warm pool to move over the islands from the E, but periods of patchy high clouds are expected to continue. A trend toward fewer showers is expected on Wednesday/Thursday, but increased PWAT moving over the islands from the E may lead to increased low clouds and light windward showers Friday and Saturday. This moisture is associated with a weak front currently in the vicinity of 30N 140W. && .AVIATION... Moderate to breezy trades will continue tonight, with showers and low cigs favoring windward and mauka locations. Periods of MVFR conditions are possible in any showers, which are expected to increase in coverage during the late night to early morning hours. Otherwise, VFR conditions should prevail. Trade winds are expected to strengthen slightly to become locally strong during the next 24 hours. 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 this evening and might need to be expanded to include windward sections of some of the smaller islands later tonight as shower coverage increases. && .MARINE... A high pressure system north of Hawaii will strengthen keeping fresh to strong trade winds in the forecast for most areas, and near gale- force winds for some of the windier eastern channels. A Small Craft Advisory (SCA) remains in effect for most waters around the Big Island and Maui County. As the high settles far north of the islands Thursday and Friday, trade winds will increase a notch, and the SCA will likely be expanded and continue through the weekend. The current south swell will fade out tonight, followed by a lull in south shore surf into Friday. A mix of small, long period south and southwest swell may push shores up near seasonal average during the weekend. As these swells slowly decline early next week, another small long period south-southwest swell is expected to fill in. Surf along east-facing shores will gradually trend up Thursday through the weekend. The trade wind swell is currently just under seasonal average at about 6 to 7 feet at 7 to 8 seconds. Expect a slight increase late Wednesday or Thursday, followed by a rise above seasonal average this weekend. Surf along north-facing shores will return to seasonally tiny levels tonight as a small northwest swell fades. Additional very small 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