Forecast Discussion

Synopsis

21 Feb 2025 13:14:00 GMT: Light winds and mostly dry conditions will prevail through early next week, with a few showers possible along windward slopes and coasts at night and over the island interiors each afternoon. Areas of vog will be possible at times during the next couple days due to a recent increase in volcanic activity on the Big Island. A front will approach from the northwest around the middle of next week bringing an increase in showers, particularly over the western end of the state.

Discussion

21 Feb 2025 13:14:00 GMT: Currently at the surface, a 1025 mb high is centered around 1700 miles east-northeast of Honolulu, with a ridge extending southwestward to a location around 175 miles north of Kauai. The resulting gradient is producing light to moderate trades across the island chain early this morning, with land breezes present in some of the more terrain sheltered locations. Infrared satellite imagery shows partly cloudy conditions in most areas, with a bit more cloud coverage in some windward and mauka locales. Radar imagery shows a few light showers moving into windward areas, as well as brushing the the leeward Big Island coast. Main short term focus revolves around wind trends and rain chances. The ridge of high pressure north of the islands will gradually weaken today through Saturday, allowing land and sea breezes to become common over the western islands, while light to moderate trades hold over the eastern end of the state. A new high building north of the area could bring a brief return of light to moderate trades across the entire island chain late Sunday, but this appears short lived as an approaching front eases the trades again Monday. Light to moderate trades may fill back in again Tuesday, followed by a transition to more southerly flow at light to moderate speeds Wednesday and Thursday in advance of another approaching front. As for the remaining weather details, mostly dry and stable conditions should prevail through Tuesday, with significant moisture sources associated with decaying fronts remaining to the north and west of the state. There will still be a few showers moving into windward slopes and coasts each night, with a few daytime heating showers possible over the island interiors each afternoon. Rainfall amounts should remain light however with low and mid level ridging keeping inversion heights suppressed over the state. As winds turn southerly in advance of another front Wednesday and Thursday, the boundary layer should moisten up and inversion heights should rise, bringing an increase in showers, particularly over the western end of the state.

Aviation

21 Feb 2025 13:14:00 GMT: A surface ridge north of the islands will support light to moderate E to SE winds. A strengthening ridge aloft will lead to increasing stability, with isol SHRA. MVFR cigs can be expected windward and mauka but VFR should prevail. No AIRMETs are anticipated.

Marine

21 Feb 2025 13:14:00 GMT: High pressure over the northeast Pacific will hold through the week. A ridge extending from the high and passing just north of Hawaii will drive moderate east winds through the morning hours. The ridge will shift south today causing low level winds to weaken and shift to the east-southeast by evening. Light trade wind flow will then persist through the remainder of the weekend and into the coming week. The current west northwest swell will continue its gradual decline. The next significant northwest swell is due late Saturday into early next week with peak surf heights likely reaching warning levels along north and west facing shores. Yet another similar sized northwest swell is expected to build in Tuesday night and linger through Wednesday night. Small surf is expected along east facing shores over the next week as trade winds remain light. Surf along south facing shores should see a small boost as a small south swell fills in on Friday and Saturday.