Strong trades develop this weekend as a tropical system delivers heavy rainfall to windward and southeast slopes of the Big Island. A Flood Watch remains in effect for the Big Island.
A surface trough continues to move west and should clear Kauai this morning. The trough is maintaining light winds over the western islands, allowing for localized land and sea breezes. Behind the trough, trades are starting to fill back in, and will begin to fill back in and strengthen gradually across the island chain from east to west. Trade winds will continue to strengthen on Saturday and AIRMET TANGO will likely need to be issued for low level turbulence.
Due to the lighter wind flow pattern, clouds and showers will likely form over the interior regions and elevated terrain this afternoon and then transition to mainly windward locations this evening into tonight. Background southeast flow this morning has pushed some clouds and showers up against the mountains producing some MVFR conditions on Kauai, Oahu, Maui and the Big Island. As such, AIRMET SIERRA is in effect for mountain obscuration. The smaller islands are expected to clear later this morning, and the Big Island will persist into the afternoon hours. Otherwise, VFR conditions are expected to prevail.
Issued at 355 AM HST Fri Aug 21 2026
A trough passing north of Kauai this morning will continue to track northwestward and away from the state. As the trough moves away, moderate to locally fresh trades will return later this afternoon and could become locally strong tonight. A Small Craft Advisory (SCA) will likely be needed for the windier waters around Maui County and the Big Island by late tonight. Trade winds will continue to strengthen over the weekend with gale force winds possible across the windier waters around the Big Island as Tropical Depression Two-C passes south of the state. A Gale Watch will be possible for some of the windier waters around Maui County and the Big Island late Saturday into Sunday. Across the offshore waters, Tropical Storm conditions will be possible as early as late Saturday. Tropical Storm conditions are expected Saturday night into Sunday across the southern offshore waters.
Surf along south facing shores will see a modest increase today from a new long-period south swell that began trickling in yesterday. Another reinforcing swell is expected over the weekend, which should boost surf heights near the summer average over the weekend. A series of south swells are expected next week with above average surf likely during the second half of next week. Surf along east- facing shores remains below average with weak trades, then is expected to build this weekend as the trades restrengthen. Surf along east and south- facing shores will be compounded by a southeast swell generated by Tropical Depression Two-C that will build through Sunday and then become south, then southwest through early next week. This short- period tropical swell could cause surf to approach advisory levels along east facing shores of the Big Island Saturday night into Sunday, though forecast confidence is on the lower side as the wind field with this tropical cyclone is expected to be relatively small and the forecast track may shift slightly. North facing shores will remain tiny through today, with a slight bump from Hurricane Lala possible this weekend out of the west-northwest direction.
Flood Watch from late Saturday night through Monday afternoon for Big Island East-Big Island Interior-Big Island North-Big Island South-Big Island Southeast-Big Island Summits-Kohala-Kona.
