textproduct: Honolulu

SYNOPSIS

High pressure passing to the north will bring a brief return of moderate to locally breezy easterly trade winds from this afternoon into Saturday. An upper level trough will bring a slight chance of thunderstorms over the Big Island slopes this afternoon and over Kauai late this afternoon into tonight. From Sunday into early next week, a series of disturbances passing near the state will produce light and variable winds and increased shower chances over the western portion of the island chain.

SHORT TERM UPDATE

Issued at 910 AM HST Fri Apr 17 2026

The forecast remains on track today, with a few heavy showers and thunderstorms possible over select areas. Surface high pressure moving eastward far north of the islands will bring a return of moderate trades, which will focus modest showers across windward slopes. Weak ridging aloft centered east of the Big Island has brought clearer skies during the past 24 hours, but an upper level trough slowly advancing toward the state from the west will produce another increase in high clouds and some instability. As a result, isolated heavy showers may develop across leeward and interior Big Island and Kauai this afternoon, with some chance of thunderstorms lingering around Kauai tonight.

PREV DISCUSSION

Issued at 405 AM HST Fri Apr 17 2026

At the surface, high pressure building north of the state will cause the trade winds to strengthen today especially during the afternoon. Moderate to locally breezy trades should fill in during the afternoon and will likely persist through Saturday. In the upper levels of the atmosphere, we have a short-wave trough swinging through the state today, which will bring an increase of mid to high clouds and provide some instability. Thunderstorms have already been developing along this short-wave trough this morning and while most of the thunderstorm activity is expected to stay west of the state, a slight chance of thunderstorms remain over Kauai later this afternoon through tonight. Over on the Big Island slopes, day time heating should lead to afternoon convection and we could see a few thunderstorms develop once again this afternoon. Any thunderstorms that develop along the slopes will be short-lived with the threat for any lightning decreasing in the evening hours. Elsewhere across the state, fair weather conditions are expected with moderate to locally breezy trade winds.

Over the weekend, another trough developing west of the state will cause the winds to weaken and veer towards the southeast by Sunday. As the flow veers more southerly, deeper moisture will spread northward across the state, especially over the western half of the state, where the GFS model is showing precipitable water values approaching 2 inches around Kauai. Abundant moisture and another upper level short-wave trough swinging through could bring the threat of heavy rain Sunday afternoon into Monday for Kauai and possibly Oahu. The forecast for Sunday into Monday will likely evolve over the next 24 to 36 hours as we get more data from our high resolution models, so stay tuned.

Beyond Monday, we will likely continue to see some lingering moisture over most of the state through the middle of next week. Light winds during this time will allow for afternoon sea breezes to develop, which will allow for afternoon clouds and showers to develop especially over interior and mountain areas.

AVIATION

Issued at 910 AM HST Fri Apr 17 2026

Mid- and upper-level cloud cover will pass intermittently over the islands today. An upper level disturbance may provide a slight uptick of showers around Kauai this afternoon with isolated thunderstorms. Isolated thunderstorms will also be possible over interior Big Island this afternoon. Elsewhere, showers should be limited to mainly windward and mountain areas with brief periods of MVFR ceilings and visibility.

Easterly trades are expected to strengthen to moderate to locally breezy through the day as surface high pressure builds to the north of the region. Heading into Saturday, winds may veer east-southeasterly as a weak trough approaches the state from the northwest.

AIRMET ZULU remains in effect for tempo light icing over the Big Island. This will continue for the next several hours as mid and upper level moisture lifts northward over the area.

MARINE

Issued at 405 AM HST Fri Apr 17 2026

A weak trough N of the state will continue to move NE and away from the area today. High pressure then builds N of the area into the weekend, which will allow trade winds to gradually strengthen this afternoon into tonight. Moderate to fresh trade winds are expected across area waters by this afternoon with locally strong trades expected over the windier waters around Maui County and the Big Island. A Small Craft Advisory (SCA) has been issued for the windier waters through Saturday. A trough developing to our W and NW on Sunday will cause trades to weaken slightly and veer to ESE. Gentle to moderate ESE winds are expected Sunday into early next week.

Small background energy from the W will be possible this weekend into next week from Typhoon Sinlaku, but confidence remains low. A moderate NW to WNW swell is possible towards the second half of next week as Typhoon Sinlaku transitions to extratropical early next week. Low pressure advancing S along the W coast of the US next week should produce a moderate, medium period NE swell toward the islands by midweek.

A small to moderate, medium-period, SSE swell boosts surf along S shores through today then lowers over the weekend. Surf is expected to return to background levels along south facing shores by early next week. Surf along E shores remains below the seasonal average as trades remain light. However, increasing trades by week's end should bring a slight bump to surf over the weekend.

HFO WATCHES/WARNINGS/ADVISORIES

Small Craft Advisory from noon today to 6 PM HST Saturday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters-Maalaea Bay-Pailolo Channel.