textproduct: Honolulu

SYNOPSIS

Moderate trades will strengthen to moderate to breezy Wednesday and hold into the weekend. Moisture will increase across the state from east to west today through Friday increasing chances of showers mainly for windward and mauka areas. Chances of heavy rain and flood potential for windward areas looks to develop Thursday through Friday as an upper level disturbance moves overhead. Drier air will move back in this weekend as trades continue. Moisture from the remnants of Tropical Depression 15-E may bring another round of enhanced showers early next week.

SHORT TERM UPDATE

Radar and satellite show mainly light to moderate showers focused along windward and mauka areas. Moderate to locally heavy showers can be seen just upstream of Oahu and Kauai so have increased the POPs and QPF slightly this morning and afternoon for windward locations of these islands as these showers are expected to move over the area within a northeast trade wind flow. Have also removed chance of thunderstorms for upslope windward and southeast Big Island this afternoon as mid level ridging should keep the atmosphere stable for the most part. Expect moderate to brief heavy trade wind showers to increase along windward and mauka locations tonight as the airmass continues to become more saturated.

Forecast remains on track for Wednesday with chances of showers increasing as remnant moisture from Norbert fills in from east to west. Latest guidance shows the best upper level support for heavy rain and flood potential developing Thursday. Thus a flood watch maybe be issued as early as Wednesday.

PREV DISCUSSION.

Issued at 323 AM HST Tue Sep 15 2026 Radar and satellite show showers mainly offshore to the north of Maui County and Oahu this morning. Only isolated showers were noted over land, mainly Molokai. Winds averaged 5 to 15 mph.

A large surface high pressure system centered almost 2000 miles northeast of the state dominated the Pacific between Hawaii and Alaska this morning. This high will weaken and slide slowly southeast through the week, as a trough moves east across the northern Pacific. Trades will continue to bring ENE to E winds to the region. Embedded in this flow is an area of moisture from the remnants of Norbert, and this moisture will bring a sharp increase in showers from late Wednesday night through early Friday. Instability will be sufficient for an isolated thunderstorm as well. Heavy rain is possible, and a flood watch may be needed as we get closer in time.

Moisture will decrease late Friday through the weekend, but the latest guidance shows that another area of increasing moisture (from the remnants of tropical depression 15-E) will likely move into the area Monday or Tuesday next week. The GFS is especially bullish with this moisture, showing PW values over 2 inches. The ECMWF is not as wet. A better estimate of how much moisture this system will bring should be available by Friday, just as the initial moisture from the remnants of Norbert depart. Trade winds are forecast to be moderate to breezy starting Wednesday and lasting into early next week.

AVIATION

No major changes to the forecast as moderate trade winds prevail this morning. The trade winds will gradually strengthen to become locally breezy this afternoon into the evening. Moisture will continue to gradually increase as well throughout the day and increase windward cloud and shower coverage as it passes through. MVFR conditions will be possible in passing showers. Otherwise, VFR conditions will prevail.

AIRMET Sierra is in effect for tempo mountain obscuration for windward areas of the Big Island through Oahu and may be needed through the morning hours as showers linger.

MARINE

Issued at 323 AM HST Tue Sep 15 2026 Moderate to locally fresh trade winds will persist today as a weak trough lingers to the northeast. By Wednesday, high pressure building north of the islands will increase the trade winds into the fresh to locally strong range through the weekend. Also by Wednesday afternoon, the remnants of Norbert will begin to move into the offshore waters as a trough and increase shower coverage as it traverses east to west across the islands, potentially through the weekend.

A series of long-period south to southwest swells will fill in through the week, leading to a gradual increase in surf for south-facing shores through the week. The first pulse fills in today into Wednesday out of the southwest, followed by larger south-southwest swells Friday into the weekend. Small surf is expected through Wednesday, after which an upward trend is expected, and surf could approach advisory thresholds by this weekend.

Surf along east-facing shores should see a gradual increase this week as trade winds strengthen and a small, medium-period east swell from Tropical Storm Norbert arrives. Flat to tiny surf along north facing shores is expected through the forecast period.

FIRE WEATHER

Issued at 323 AM HST Tue Sep 15 2026 Fire weather risk should remain low through the remainder of the week due to light to moderate winds and the effects of recent (and upcoming) rainfall. Inversion heights from Maui to the Big Island should be 7000 to 8000 ft through Wednesday. Showers will dramatically increase from late Wednesday into early Friday, keeping vegetation moist.

HFO WATCHES/WARNINGS/ADVISORIES

None.