textproduct: Honolulu

SYNOPSIS

A slightly unstable trade wind flow will prevail today as a weakening upper level low produces isolated heavy showers and thunderstorms, mainly on the Big Island. Somewhat wet easterly trade winds will focus most rainfall along windward slopes Sunday into early next week. A more stable, moderate to breezy trade wind flow will develop Tuesday and Wednesday.

DISCUSSION

Heavy showers and thunderstorms decreased dramatically yesterday evening as the upper level low over the islands weakened, and easterly trade winds have focused mainly moderate showers over windward slopes overnight. There is some lingering instability from the upper low, but so far, only a few heavy showers have briefly flared up, even with a steady supply of low level moisture streaming into windward Big Island. Given recent trends, the Flood Watch has been cancelled.

Chances of heavy showers and thunderstorms will diminish today as the upper low drifts eastward and weakens. Moderate easterly trade winds will focus rainfall over windward areas of all islands, with more shower activity expected on Big Island due to increased low level moisture filtering in from the east. Lingering instability from the departing upper level low could also trigger isolated heavy showers and thunderstorms on the Big Island, but the threat of flooding does not appear high enough to continue the Flood Watch today.

Moderate easterly winds and a somewhat wet pattern of mainly windward and mauka showers is expected Sunday into early Tuesday. The upper low will be replaced by a broad and flat upper trough, which will not allow the atmosphere to become very stable. As a result, we cannot rule out a briefly heavy shower, mainly over the heated leeward slopes of the Big Island and Maui during the afternoon hours.

Increased stability and stronger trade winds are due late Tuesday or Wednesday. Expect a typical pattern of mainly windward rainfall and mostly dry conditions leeward.

AVIATION

An upper level low continues to weaken this morning just north of the Big Island. Expect an unsettled trade wind weather pattern with brief periods of MVFR conditions. Shower trends will decrease through the weekend as the upper low continues to weaken and march eastward.

AIRMET Sierra remains in effect for mountain obscuration over Kauai, Oahu, Molokai, and Big Island.

MARINE

Winds will remain slightly east southeasterly this weekend at moderate to fresh levels. The upper level disturbance that gave us some severe weather yesterday will be moving northeast away from the state, with stability slowly returning to the region. As a result, expect decreasing showers and thunderstorms across the waters. A more typical easterly trade wind pattern will return next week.

A small, medium period north northwest (320-330 degree) swell that peaked overnight will continue to decline. Surf along north and west facing shores will follow suit, easing during the weekend.

A mix of small, medium to long period south swells will maintain small surf along south-facing shores this weekend. A series of gale lows passing south of New Zealand should send small south swell energy into the southern waters through next week. Surf should lift to summer averages around Sunday and hold through Wednesday. Moderate to fresh trades will maintain rough and choppy surf along east-facing shores.

Tides will peak around 2.5 to 3.0 ft MLLW this weekend. Minor overwash of low lying coastal areas will be possible during times of high tide.

HFO WATCHES/WARNINGS/ADVISORIES

None.