textproduct: Honolulu

SYNOPSIS

An unstable and somewhat wet trade wind pattern will continue through mid-week, with brief downpours possible. During the second half of the week, a strengthening area of high pressure north of the islands will increase stability across the region, producing drier, but windier conditions.

UPDATE

Trade showers continue this morning, with rainfall reports between 1 and 2 inches at higher elevations, but only 0.10 to around 0.40 at lower elevations. Today should end up looking much like yesterday, with additional showers, mainly windward and mauka, through the day. Some of these showers may be heavy due to high PW values, and a few will spill over to (or develop in) leeward areas. All this is handled well by the current forecast and no update is planned at this time.

PREV DISCUSSION

Issued at 342 AM HST Mon May 18 2026 This morning, local satellite and radar imagery shows just a few light scattered showers moving into the islands on moderate easterly trade wind flow. While some areas of the state received significant rainfall totals yesterday, shower intensity and coverage eased area-wide after sunset. With that said, the early morning sounding from Hilo continues to show over two inches of precipitable water, compared to the much drier Lihue sounding. Broad troughing aloft persists over the islands, and with this amount of ample moisture available, expect that a generally wet trade wind pattern will continue for the next couple of days with frequent showers over windward areas, especially for the Big Island. Some showers could produce brief downpours, similar to those that were observed this past weekend at times. Showers will generally favor windward areas during the overnight and morning hours, with scattered leeward showers developing during the afternoons. Additionally, dewpoints will continue to linger in the upper 60s to low 70s, which should make temperatures feel warmer than normal.

Increased stability and stronger trade winds are expected by Thursday. Latest global guidance remains in good agreement with a strong high developing far north of the state during the second half of the week, which should result in windy conditions. Winds could potentially reach Wind Advisory levels Thursday into Friday for select areas downstream of terrain. Drier conditions are also expected during this time, but scattered showers embedded within the windy trade wind flow will continue, especially during the night and early morning hours.

AVIATION

Moderate to locally breezy trades expected for the next couple days. Low cigs and SHRA should primarily impact windward and mauka locations with some limited spillover to leeward areas. MVFR conds possible in heavier SHRA, otherwise VFR prevails.

AIRMET Sierra is in effect for mtn obsc for Kauai, Oahu, Maui and windward sections of the Big Island.

Will continue to monitor for possibly adding AIRMET Tango for moderate low level turbulence through the afternoon as tradewind strengthen slightly.

MARINE

A surface high centered about 1,400 nautical miles northeast of the islands will generate moderate to locally strong trades over the next few days. This anchored high will strengthen and expand during the second half of the week and will cause the trade winds to strengthen to widespread strong speeds with near gales over the windier zones around Maui County and the Big Island. A Small Craft Advisory (SCA) is currently in effect for the windier zones around Maui County and the Big Island. The SCA will expand in area later this week as the trades strengthen.

A small size, short to medium period north northwest is expected on Tuesday. Otherwise, another small north northwest bump is possible over the weekend.

A series of small long-period south-southwest swells will provide surf near the summer average along south facing shores throughout the week. Strengthening trades later this week will bring an increase of short-period energy and will bring elevated surf along east facing shores by Thursday or Friday.

Water levels peaking between 2.5 to 3.0 ft MLLW during today's high tides may result in some minor overwash within low lying coastal areas this afternoon.

HFO WATCHES/WARNINGS/ADVISORIES

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