Swell Matrix

Area Forecast Discussion

National Weather Service Honolulu Hi

321 pm hst Tue apr 21 2026

Synopsis

A light land and sea breeze pattern will produce afternoon clouds and spotty showers over land and partial clearing at night. Trade winds will redevelop late Wednesday and strengthen Thursday and Friday focusing rainfall over windward and mauka areas.

Discussion

A humid land and sea breeze regime will prevail over the next 24 hours or so. Isolated showers near the coasts will dissipate during the early morning, followed by interior clouds and spotty showers in the afternoon. While stability is slowly returning, a briefly heavy shower is still possible in the afternoon and evening.

Trades will slowly redevelop on Wednesday as the low to the north drifts east and weakens. The combination of the building trades and gradually increasing stability will lessen chances for afternoon showers. Trade winds will strengthen Thursday and Friday and will persist into early next week as surface high pressure becomes established north of the islands. The moderate to locally breezy trades and more stable conditions will push dew points back into the lower 60s, providing relief from the recent humidity. Showers will become focused over windward slopes.

Aviation

Land-sea breeze pattern can be expected into Wednesday as background wind regime remains light and variable. Onshore sea breezes will keep clouds and light showers possible over island interiors rest of this afternoon. Land breezes will develop shorty after sunset, helping to clear these interior areas of clouds and decrease chances of rainfall. Winds will gradually become light to gentle out of the northeast Wednesday, but could remain light enough for afternoon seabreezes to develop Wednesday afternoon for sheltered areas. Moderate to locally breezy tradewinds will return Wednesday evening allowing for a more typical tradewind pattern to return and hold through the rest of the week. Expect mostly VFR with brief MVFR conditions possible in cld and shra.

No AIRMETs in effect.

Marine

A weak low north of the area will continue to drift eastward and further away from the state over the next few days. As the low drifts further east, a ridge of high pressure will fill in north of the state, which should bring the return of moderate trade winds by Wednesday evening. Light winds during the night tonight and day time Wednesday will lead to land and sea breeze development near the coastlines. By Thursday evening, we should see moderate to fresh trade winds and by the weekend, we could see moderate to locally strong trade winds as another high builds north of the state.

A small, medium-period, west-northwest to northwest (300-330) swell continues to fill in this afternoon and will likely peak tonight, then gradually decline over the next few days. Another smaller reinforcing swell will also fill in tonight into Wednesday.

A moderate, medium-period north-northeast swell also started filling in today and will likely peak on Wednesday near advisory thresholds for east facing shores. This swell will produce above average surf for select north and east facing shores on Wednesday, before slowly declining through the end of the week. Strengthening trades late this week will support closer to seasonal average surf for east facing shores into the weekend.

As the former Super Typhoon Sinlaku made its extra tropical transition last weekend, it gradually traveled eastward along our great circle route. Although the former typhoon was relatively compact, altimeter did show some higher seas of 14 to 18 feet far west of the state a few days ago. This could bring some west swell along select exposures starting today through the next several days. Peak energy from the former Typhoon is expected Wednesday or Thursday and could wrap into select southwest facing exposures. Otherwise a small southwest swell from the Tasman Sea should arrive this weekend.

Watches, Warnings, Advisories

None.

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