FORECAST DISCUSSION

Synopsis

A trough aloft west of Kauai will keep the atmosphere unstable near the islands through at least the coming weekend. A surface low north of the islands will move away to the northeast today and a weak ridge will persist north of the area through Thursday and produce gentle trade winds. The trades will be light enough to allow afternoon sea breezes to develop and produce clouds and showers over interior area. Nighttime land breezes will produce partial clearing at night. The trough aloft will deepen late in the week. The surface winds will shift out of the southeast and bring an increase in rainfall.

Discussion

A trough aloft west of Kauai has weakened over the past 24 hours and a surface low north of the area is moving away to the northeast. A weak ridge will build north of the area today and produce gentle trade winds over the islands. The winds will remain light enough for daytime sea breezes and nighttime land breezes to prevail through Thursday. The trough west of the area will keep the atmosphere unstable enough to allow locally heavy showers to develop during the afternoons and evenings. The land breezes will bring partial clearing during the late nights and early mornings. The trough aloft will deepen again Thursday. Winds near the surface will veer out of the southeast by the end of the week and the atmosphere will become more unstable. This may bring another period of more widespread rain by Friday. There continue to be differences in the global models beyond a few days out, so longer term forecasts remain uncertain.

Aviation

VFR will prevail at terminals from Kauai to Molokai today, with occasional MVFR on Maui and the Big Island. AIRMET Sierra remains in effect for mountain obscuration from Molokai eastward to the Big Island. Conditions are expected to improve over Oahu later this morning. Molokai and Lanai should see improving conditions by this afternoon, and Maui and the Big Island may deal with mountain obscuration through much of the day. AIRMET Tango is in effect for moderate upper level turbulence between 150 and FL350 across all islands due to a trough aloft west of Kauai. These conditions are expected to improve later today. AIRMET Zulu is in effect for icing from Molokai eastward. These conditions are expected to improve from west to east this afternoon.

Marine

Winds and seas are expected to remain below the advisory thresholds for the next several days. A series of northwest swells will continue, but surf will remain below the High Surf Advisory threshold.

HFO Watches/Warnings/Advisories

Flash Flood Watch to 600 PM this afternoon for Maui and Big Island.

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