textproduct: Honolulu

SYNOPSIS

A front will move over Oahu this morning before stalling and dissipating just north of the Big Island this afternoon and evening. Limited rainfall is expected Friday. Moderate southwesterly winds ahead of a stronger front will increase shower potential along leeward areas Saturday. The highest potential for heavy rainfall will develop over the western end of the state Sunday through Tuesday.

DISCUSSION

Current satellite and radar imagery shows a band of low level clouds with embedded light to moderate showers, associated with a front, moving over the north shore of Oahu early this morning. Moderate northerly winds have filled in over Kauai behind the front with light to moderate southwesterly winds ahead of the front. Overnight rainfall totals for Kauai range from .25 to 1.0 inches along windward areas with a few leeward locations receiving .01-.02 inches of rainfall. This front will continue to move SE across Oahu this morning reaching Maui County by late morning and early afternoon with mainly light to moderate showers expected. The front will stall and dissipate over Maui County, just north of the Big Island this afternoon and evening and winds will ease to light speeds allowing land breezes to develop overnight. Dewpoint temperatures will dip in the upper 50s tonight around Kauai and Oahu as drier more stable air filters in behind the front.

Friday winds are expected to swing northeast over the western half of the state with a light southerly surge developing over the eastern half of the state. Lingering moisture from the front along with afternoon seabreezes could trigger a few showers along leeward and interior areas, especially around Maui County.

Saturday, moderate southerly winds will develop across the state as a stronger front approaches from the northwest. By Saturday night, a pre frontal convergence band may set up over the western half of the state, increasing chances of showers. There appears to be potential for isolated thunderstorm or two during this time mainly near Kauai and south waters of Oahu so have add this the forecast package this morning.

Sunday through Tuesday forecast remains on track with becoming more dynamic. An upper level trough will become negatively tilted and pinch off into a low supporting strong cyclogenesis at the surface northwest of the state. The associated band of heavy rain with the surface low will settle somewhere over the western end of the state Sunday night through Monday night. The parent upper level trough will remain rather progressive suggesting a 24-36 hour type of event. Upon the departure of supporting upper dynamics on Tuesday, the surface low will move far north of the state and weaken, leaving an orphaned frontal moisture band over the area through mid- week, maintaining lingering showers over the area. Southerly winds will prevail throughout this time keeping leeward zones in the game for rainfall for at least the next week.

Blocking high pressure over the Aleutian Island chain will continue a southward- displaced Pacific jet stream that is modeled by the EC, GFS, and machine learning guidance to settle into the low latitudes (20-25N) by the end of the forecast period. This ensures at least some potential for more active weather continuing for the foreseeable future.

AVIATION

Light west-southwesterly winds persist ahead of a front approaching from the northwest, veering more northerly behind the front. The front, currently between Kauai and Oahu, is expected to continue propagating southeastward, reaching Oahu later this morning, and then slowly diminishing over Maui County. Showers along the front may bring periods of MVFR conditions, with brief periods of IFR conditions possible. Otherwise, expect VFR conditions to prevail.

AIRMET Sierra is currently in effect for mountain obscuration across Kauai and Oahu as the front advances southeastward, however, an update may be needed later this morning to remove Kauai when the front fully passes over the island.

MARINE

A weakening cold front that has moved through Kauai this morning will slowly advance east across the Oahu and Maui County nearshore waters through the day. Gentle to moderate northerlies will occur in the wake of the front with light southwesterly winds downstream of the front. The front is forecast to dissipate in the vicinity of Maui County by early Friday morning. Another front will reach the nearshore waters late Saturday into Sunday morning. Light southeasterlies will veer more southwesterly Saturday as the front approaches, becoming more westerly. Numerous showers with locally heavy rain and isolated thunderstorms are possible in association with this front Saturday night into early next week.

Wednesday's moderate size, medium period northwest swell was reinforced by an overnight north-northwest swell and has been peaking this morning. Surf along many north and west-facing shores will remain elevated through the day. Therefore, the High Surf Advisory will remain in effect for these shores through the afternoon. Swell will slowly decline from this evening through Friday. Another moderate, long period northwest swell generated from a developing gale low just northwest of the offshore waters late Friday will travel around the islands Sunday and Monday. This swell should produce advisory level surf from Sunday afternoon through Monday morning.

Southern facing shores, especially southwestern exposures on Kauai and Oahu, may receive a moderate wind swell chop this weekend from amped up southwest winds leading an approaching front.

FIRE WEATHER

Conditions will remain below critical fire thresholds into the weekend. Inversion heights slope from 9,000 ft this morning near Kauai to 6,000 ft over the Big Island. Expect inversion heights to increase ahead of a front that is currently moving through Oahu and will settle and dissipate near Maui County this afternoon and evening. Inversion heights should level out to near 6,000 ft behind the front and as the front dissipates later tonight into Saturday.

HFO WATCHES/WARNINGS/ADVISORIES

High Surf Advisory until 6 PM HST this evening for Niihau-Kauai Leeward-Waianae Coast-Oahu North Shore-Maui Windward West-Kauai North-Molokai Windward-Molokai North-Molokai West-Maui Central Valley North-Windward Haleakala.