Moderate trades tonight will gradually strengthen each day over the next several days with widespread strong trades expected by Thursday or Friday. The main focus for the weather this week will be the tropical cyclone development southeast or south of the Big Island over the next several days. While the potential wind impacts remain uncertain, the threat for flash flooding will increase over the Big Island during the second half of the week.
Issued at 332 PM HST Mon Sep 21 2026 Moderate to locally breezy trade winds will persist as a disturbance in the deep tropics moves to within a few hundred miles south of the Big Island on Tuesday. Moisture along the northern periphery of the disturbance will gradually spreads over the island chain, leading to an increase in mainly windward rainfall. MVFR ceilings will become more widespread over windward slopes. AIRMET Sierra for mountain obscuration remains in effect for windward Big Island and will likely be expanded to additional islands overnight and Tuesday. Aside from scattered afternoon SHRA over the Kona slopes of Big Island, VFR will dominate over leeward areas.
With trades remaining at moderate to breezy strength, AIRMET Tango for moderate low level turbulence downwind of island terrain will
Issued at 332 PM HST Mon Sep 21 2026 The gradient between high pressure to the northeast and an approaching trough that may develop into a tropical cyclone to the southeast will maintain moderate to locally strong trade winds through Wednesday. A Small Craft Advisory is in effect for the typical windy waters of Maui County and the Big Island through early Wednesday morning. Wind speeds will strengthen during the latter half of the week as the trough or potential tropical disturbance moves near the islands. Shower coverage will also increase, along with the potential for isolated thunderstorms, particularly across the eastern waters.
Surf along south facing shores will remain above average through this afternoon, then will gradually drop heading into midweek as the current south-southwest swell fades. A slightly smaller, long-period south-southwest swell will fill in late this week into next weekend generated by a series of lows near New Zealand. West facing shores will experience a bit of the southerly wrap through most of the week.
Breezy trade winds will maintain moderate surf along east facing shores for the next several days. Surf along north facing shores will remain flat to tiny through tonight, but will see a bump heading into Tuesday and Wednesday as a small, medium-period north-northwest swell fills in from an Aleutian low. Then a small, long- period west-northwest swell generated by Typhoon Dujuan as it curves northeast near Japan will build locally Friday into next weekend, increasing surf along north and west facing shores.
Small Craft Advisory until 6 AM HST Wednesday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.
