textproduct: Honolulu

SYNOPSIS

Moderate to locally breezy trade winds will continue tonight, with periods of showers favoring windward mountain areas. An upper level low will briefly move over the region today and tonight, enhancing threats for locally heavy rainfall and isolated thunderstorms. Expect periods of heavy showers along with isolated to scattered thunderstorms today across the islands in Kauai County, Oahu, and Maui County. A wet trade wind weather pattern however will likely continue through Sunday morning for most areas. More typical trade wind weather will return from late Sunday into the end of next week with brief passing showers in the forecast as moderate to locally breezy trade winds continue to blow across the region.

SHORT TERM UPDATE

Strong showers and a few thunderstorms continue to develop ahead of and under the approaching upper low. Heavy rain is occurring, but so far the precipitation is moving NNE along at around 15 mph, so there is a relatively low chance for flooding at this time. However, the latest guidance is consistent with a continued threat of flooding through today, and the flood watch will remain in effect unchanged. There is a good chance that it will be extended through tonight in some areas, and Big Island may need to be added. These decisions will be made in the afternoon forecast, giving us time to fully include the latest data over the next few hours.

PREV DISCUSSION

Issued at 301 AM HST Fri May 15 2026

An unstable upper level low continues to drop into the islands from the north this morning with thunderstorms forming less than 100 miles north of Niihau, Kauai, and Oahu. Expect periods of heavy showers along with isolated to scattered thunderstorms today across the islands in Kauai County, Oahu, and Maui County. A Flood Watch was issued through this afternoon for these islands due to the heavy rain and flooding threats across most of the state. This watch may need to be extended into the overnight hours for some areas as this upper low pivots over Kauai, then weakens and drifts eastward across the state.

Unstable cold air aloft within this upper level low will enhance shower activity statewide, showers will become heavy at times with isolated to scattered thunderstorms. Small scale low level wind convergence bands and thunderstorm outflows will likely drive the heaviest shower activity today. Higher rainfall rates will likely lead to flash flooding in some areas through at least the afternoon hours and possibly into the overnight time period. This low will slowly weaken as it drifts eastward on Saturday, decreasing the threat for heavy rainfall, especially as the low departs the Hawaii region on Sunday. A wet trade wind weather pattern however will likely continue through Sunday morning for most areas.

A broad high pressure ridge remains in place north of the islands through much of next week. Expect a more typical moderate to locally breezy trade wind weather blowing across the Hawaiian Islands from late Sunday into the end of next week. Brief passing showers will occur favoring the windward mountain areas in the overnight to early morning hours.

AVIATION

Surface trough near Kauai this morning will result in gentle to moderate trade to ESE winds (90 to 120 degrees) across the state. Upper low tracking over the western half of Hawaii today will destabilize the atmosphere producing scattered heavy showers and thunderstorms, particularly across Kauai and Oahu. SIGMET Zulu is posted for thunderstorms across waters just north of Kauai and Oahu this morning. This SIGMET may be moved over either/both Kauai and Oahu later today and tonight as the upper low digs slowly southward. The upper low is expected to weaken through the day Saturday, while shifting heavy rain/thunderstorm threat to Maui and Big Island.

AIRMET Sierra is in effect for tempo mountain obscurations above 2000 feet for entire area of Kauai and Oahu, and for windward and southeast slopes of the Big Island. It's possible AIRMET Sierra could expand to portions of Maui County at some point later today, but likely the areas in effect now will continue into this evening. AIRMET Tango is posted for tempo moderate turbulence all islands below 080, and associated with the jet stream from 150 to FL380. No changed are anticipated with AIRMET Tango today.

MARINE

An upper level low and its surface trough near Kauai will turn weakening winds more east southeast today and this weekend. A Small Craft Advisory (SCA) remains in effect through 6 AM HST Saturday for the eastern half of Hawaiian coastal waters. The close proximity of the upper low, along with disturbances coming up around the low from the south southwest, will produce widespread rain with periods of locally heavy rainfall and scattered thunderstorms across the nearshore waters. Some of these thunderstorms could have locally strong winds and small hail, so marine interests should monitor for Special Marine Warnings in the nearshore waters throughout the day, particularly across the western waters.

A small, moderate period north northwest (320-330 degree) swell that peaked last night is declining this morning, but will produce near to slightly above head high surf along many north- facing shores today. This swell will gradually decline into the weekend.

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

Tides will peak around 2.5 ft MLLW this weekend. Combined with ongoing trades and a small south swell bump, water levels will peak near 3.0 ft as early as tomorrow. Minor overwash of low lying coastal areas will be possible during times of high tide.

HFO WATCHES/WARNINGS/ADVISORIES

Flood Watch until 6 PM HST this evening for Central Oahu-East Honolulu-Ewa Plain-Haleakala Summit-Honolulu Metro-Kahoolawe- Kauai East-Kauai Mountains-Kauai North-Kauai South-Kauai Southwest-Kipahulu-Koolau Leeward-Koolau Windward-Lanai Leeward- Lanai Mauka-Lanai South-Lanai Windward-Maui Central Valley North- Maui Central Valley South-Maui Leeward West-Maui Windward West- Molokai Leeward South-Molokai North-Molokai Southeast-Molokai West-Molokai Windward-Niihau-Oahu North Shore-Olomana-South Haleakala-South Maui/Upcountry-Waianae Coast-Waianae Mountains- Windward Haleakala.

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