textproduct: Honolulu

SYNOPSIS

A high pressure system will strengthen north of the Hawaiian Islands, producing moderate to locally windy trades. Light to moderate showers will focus over windward and mauka areas with brief showers spilling over to leeward areas, especially during the overnight and early morning hours. Winds will ease and possibly shift out of the southeast during the second half of the week and into the weekend as the high shifts northeast of the state and a weak frontal boundary approaches the state from the northwest.

SHORT TERM UPDATE

Light showers were moving onshore in windward areas this morning, with additional showers over the mountains on most islands. Winds were a touch stronger than yesterday, currently averaging 10-20 mph, with some areas gusting 25 to 35 mph. Showers should trend down slightly as we head into the afternoon, with a typical trade pattern of mostly cloudy windward and mostly sunny leeward. All this is handled well by the current forecast and no update is planned at this time.

PREV DISCUSSION

Issued at 326 AM HST Sun Oct 18 2026

Two radars are currently out of service, limiting radar coverage from Oahu to northern portions of the Big Island. Satellite imagery shows a band of low level clouds with embedded showers moving east to west across the state. Over the past 6 hours, rainfall totals ranged from 0.20 to just under 1.0 inches across windward areas, with some leeward areas seeing 0.10 to 0.75 inches.

The soundings this morning show inversion heights have increased to 10,000 ft to 11,000 ft at the Lihue and Hilo sites. These elevated inversion heights have allow windward showers to spill over to leeward areas of the smaller islands overnight.

Inversion heights will drop to near 4,000 ft for the western half of the state and near 7,500 for the eastern half of the state as drier air filters in during the day today. This will lower rainfall chances, focusing precipitation mainly along windward slopes.

Another band of low level clouds with embedded showers will increase chances of rain tonight into Monday. Combined with elevated inversion heights, brief showers will again spill over to leeward areas of the smaller islands.

The remainder of the short term forecast generally repeats this pattern of passing light showers focusing along windward and mauka areas during the day and slightly enhanced showers overnight with spillage to leeward areas driven by showers embedded in the trade wind flow and lingering instability aloft.

A surface high to our north will strengthen today, allowing winds to become breezy to locally windy at higher elevations and ridges. Gusty winds will also develop downslope of leeward areas this afternoon has inversion heights lower. These conditions will hold through the first half of the week with minor fluctuations.

The second half of the week and into the weekend the high is expected to shift northeast of the state as a weak front approaches from the northwest. This will result in surface level winds weakening and possibly allow for a hybrid trade wind and land/sea breeze pattern to develop. In addition, upper level instability from a trough swinging from the northwest to southeast over the state could make for enhanced showers during this time. However timing and position of the upper level trough and surface front start to diverge between the GFS and ECMWF deterministic guidance thus there remains low confidence in the extended forecast at this time.

AVIATION

Breezy trades will persist through the forecast period. Isolated to scattered showers will be concentrated mainly along windward and mauka locations, most numerous late at night through the mornings. Some of the showers may produce brief periods of MVFR ceilings and visibility.

AIRMET Sierra remains in effect for north through east sections of the Big Island below 2500 feet due to low clouds and showers. Sierra will likely be canceled later this morning as conditions improve.

AIRMET Tango remains in effect for for tempo moderate turbulence downwind of terrain below 9000 ft.

MARINE

Robust surface high pressure centered far north of Hawaii will maintain fresh to near gale force trade winds into Tuesday. A Small Craft Advisory (SCA) remains in effect for all waters except windward Big Island through Monday morning but will need to be extended through at least early Tuesday. Trades will steadily decrease late Tuesday and Wednesday as the high weakens and is displaced eastward by an approaching low far northwest of the islands. Trade winds may lower to gentle strength or may become disrupted as the low passes to the north Thursday.

A north-northwest swell and a smaller overlapping west-northwest swell will slowly decline through Monday and fade on Tuesday. A very small northwest swell may arrive Thursday, followed by a moderate north- northwest swell next weekend.

The current south swell will continue a slow decline today. South shore surf will drop below seasonal average Monday and will remain relatively small through much of the week. A moderate south- southwest swell is expected next weekend.

Rough trade wind swell will produce east shore surf just above seasonal average through Tuesday, then decline later in the week as trade winds decrease.

FIRE WEATHER

Issued at 326 AM HST Sun Oct 18 2026

Fire weather conditions could reach near critical for select leeward locations downwind of ridges as breezy to locally windy conditions develop and minimum humidity levels dip near critical levels for the next couple of days. During the second half of the week, below critical fire weather conditions may develop as winds ease to light to moderate levels and minimum relative humidity rebounds each afternoon. The subsidence inversion heights near Maui and the Big Island will range from 7,500 to 8,500 this afternoon.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory until 6 AM HST Monday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Kaiwi Channel-Kauai Channel-Kauai Leeward Waters-Kauai Northwest Waters-Kauai Windward Waters-Maalaea Bay-Maui County Leeward Waters-Maui County Windward Waters-Oahu Leeward Waters-Oahu Windward Waters-Pailolo Channel.