textproduct: Honolulu

SYNOPSIS

A weakening high pressure ridge north of the Hawaiian Islands will keep trade wind speeds on the decreasing trend lasting into Saturday, then ridge and wind speeds strengthen from Saturday afternoon into early next week. Passing showers are possible over windward and mountain areas during this time period, mainly during the overnight to early morning hours. The next best chance for statewide rainfall may develop from Monday into Tuesday of next week, as the cloud remnants from an old cold front drift across the islands on the trade winds.

DISCUSSION

Radar shows isolated trade showers moving into most windward areas this afternoon. A few are still making it over to leeward areas, but rainfall amounts have been very light (just a few hundredths of an inch). Winds were averaging 10 to 20 mph, and the normal windy locations were gusting near 30 mph.

Weak upper level ridging will remain in place near Hawaii through the weekend. At the surface, a high pressure system will move from our northwest to our northeast. Monday, an upper level low will approach from the northwest. At the same time, but unrelated, a band of moisture associated with an old frontal boundary will move across the state from the northeast. This should lead to a brief increase in showers, but no significant rainfall is forecast. The best guess on timing for this band, according to the latest guidance, is Monday evening.

The upper level low will continue to weaken as it moves very close to Hawaii Wednesday into Thursday. With minimal cold air aloft, it is expected to result in a slight increase in instability, perhaps leading to a slight increase in both the coverage and intensity of showers. A new ridge aloft is forecast to move in from the west late next week. Throughout the entire period, trades will continue.

AVIATION

Breezy trade winds along with light windward showers will continue today into Saturday. Brief MVFR ceilings and visibility are possible in any passing shower.

AIRMET Tango is in effect for low level moderate turbulence downwind of terrain.

AIRMET Sierra has been cancelled. Lingering low clouds were noted over the northern Koolaus and the Kawailoa Forest Reserve area, but overall no longer meet widespread or extensive coverage.

MARINE

A high pressure system north of Hawaii will slowly weaken through the remainder of the day, allowing trade winds to slightly decrease tonight. A Small Craft Advisory (SCA) is in effect for the typical windy waters near Maui County and the Big Island. By tomorrow evening, a new high pressure will build north of the islands and restrengthen trade winds, likely leading to an expansion of the SCA to include additional waters. Next week will likely see continuing fresh to strong trades with some minor fluctuations each day. A moderate to large north northwest swell is also expected to fill in early Sunday morning and elevate coastal waters seas above 10 feet.

A moderate, north-northwest swell will continue to decline tonight into the weekend, allowing surf to become moderate to small and then small. A new small, north- northwest swell will support continued small surf into Saturday before the arrival of a more significant north swell. This moderate, long- period north swell arriving Saturday night may bring surf to advisory levels on Sunday for north and west- facing shores. Surf to at least moderate levels will last into Monday before the swell really begins to fade on Tuesday. A small to moderate northwest swell is then possible by next weekend.

Surf along east-facing shores will remain rough and choppy due to the strong trade winds this afternoon, then may decrease slightly tonight and Saturday as trades ease early this weekend. Surf will increase again Sunday into early next week as trades restrengthen. South shore surf will stay tiny to small for the next few days, then a small long period swell could boost surf heights towards the end of next week.

FIRE WEATHER

Fire weather conditions will remain below critical, limited by wind speeds for most areas and by higher minimum humidity levels for the higher elevation zones that reach wind thresholds. Wind speeds will increase into the moderate to breezy levels by late Saturday, lasting into early next week. Temperature inversion heights near Maui and the Big Island will range from 6,500 to 7,500 feet elevation through Saturday.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 PM HST Saturday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.