Swell Matrix

Area Forecast Discussion

National Weather Service Honolulu Hi

910 am hst Fri apr 17 2026

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.

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.

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.

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