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.

SHORT TERM UPDATE

Numerous showers and thunderstorms were underway on the Big Island east and southeast sides. So far rainfall rates have been light to moderate. Isolated showers were occurring on each of the other islands. The upper level system which brought showers and thunderstorms to the state yesterday is continuing to pull away to the northeast and its impact on the island will diminish through today. Wet trades are still expected tomorrow through Tuesday, with more typical trades forecast from Wednesday into next weekend. No changes are needed at this time.

PREV DISCUSSION

Issued at 336 AM HST Sat May 16 2026

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

Conditions are generally expected to be VFR today as yesterday's weather system continues to weaken and move away from the islands. Periodic windward showers and MVFR conditions cannot be ruled out, however the trend for the rest of the weekend is expected to be a gradual return towards normal trade wind conditions.

AIRMET Sierra remains in effect for mountain obscuration above 020 for Kauai, Oahu, and the Big Island, however conditions are expected to improve by the afternoon.

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 will continue to decline this weekend, with surf along north-facing shores following suit. A new, short period northwest swell will provide another small bump to surf along north-facing shores by mid-week. Surf along west-facing shores will remain mostly steady this weekend as the northwest swell influence gradually declines, but a new, long-period south southwest reinforcement arrives today.

A mix of small, medium to long period south swells will maintain small surf along south-facing shores for the next several days. The long-period south southwest swell described above will maintain small surf along south-facing shores today. Additional small, medium to long- period south swell reinforcements will arrive Sunday through mid-week. Surf along south-facing shores should lift to summer averages by Sunday and hold through Wednesday.

Moderate to fresh trades will maintain rough and choppy surf along east-facing shores for the next several days.

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.