West Kaua’i

Tonight: Mostly cloudy. Lows 70 to 75 near the shore to around 62 above 3000 feet. East winds up to 10 mph.

Thursday: Mostly cloudy. Highs 84 to 89 near the shore to around 76 above 3000 feet. East winds up to 15 mph.

Thursday Night: Mostly cloudy. Isolated showers after midnight. Lows around 71 near the shore to around 61 above 3000 feet. Light winds. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy. Isolated showers after midnight. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Mostly cloudy. Highs 80 to 88. East winds 10 to 15 mph.

Thursday Night: Mostly cloudy. Isolated showers after midnight. Lows around 72. Northeast winds up to 10 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 63 to 70 in the valleys to around 59 above 4000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Thursday: Mostly cloudy with isolated showers. Highs 74 to 82 in the valleys to around 66 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Thursday Night: Mostly cloudy with isolated showers. Lows 63 to 69 in the valleys to around 58 above 4000 feet. Light winds. Chance of rain 20 percent.

North Kaua’i

Tonight: Mostly cloudy. Isolated showers after midnight. Lows 65 to 73. Southeast winds up to 10 mph. Chance of rain 20 percent.

Thursday: Mostly cloudy. Isolated showers in the afternoon. Highs 76 to 86. Southeast winds up to 15 mph. Chance of rain 20 percent.

Thursday Night: Mostly cloudy with isolated showers. Lows 64 to 73. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy with isolated showers. Lows 64 to 77. Northeast winds up to 10 mph. Chance of rain 20 percent.

Thursday: Mostly cloudy with isolated showers. Highs 74 to 85. East winds up to 15 mph. Chance of rain 20 percent.

Thursday Night: Mostly cloudy with isolated showers. Lows 64 to 76. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Trade winds will taper off through Friday as a front approaches the islands from the northwest. The front will move north to south across the islands chain Saturday night through Monday bringing rainfall focusing on windward slopes. Strong trade winds will follow the front that will continue into next week.

Discussion

Visible satellite shows high clouds remaining across most of the state this afternoon, but beginning to thin out. A few low clouds and isolated showers are blowing in from the east with moderate to locally fresh trade winds. Expect a mostly dry night with any clouds and precipitation focused windward.
A stalled, weak trough to the north will begin to move northwest tonight in response to an approaching cold front. Winds will veer east southeasterly on Thursday before becoming light and variable by Friday. High clouds will likely lift away northeastward at this point, and localized land and sea breezes will bring a few afternoon clouds and clear nights.
The cold front is expected to arrive to Kauai Saturday night, and then begin slowing down and weakening as it moves down the island chain. Oahu and Maui will be next on Sunday, and the Big Island Sunday night into Monday. The ECMWF is a bit slower by the time it reaches the Big Island as it leans more towards Monday. Strong trade winds overruning the front will bring mostly windward showers, but many of the showers will blow over to the leeward sides of the smaller islands. There won't be any upper level support with this frontal passage. Rainfall is expected to be light to moderate but persistent and moving along, limiting any flood potential.
Breezy trade winds will continue behind the front into next week as 1038 mb sets up far north of the state. Conditions will remain stable, with scattered low clouds and showers.

Aviation

Moderate to locally breezy easterly trade winds will gradually ease and veer to the east-southeast tonight through Thursday. Low pressure to the west will continue to draw high clouds over the western end of the state this evening. VFR conditions will prevail with a brief periods of MVFR conditions over windward and mountain areas.
No AIRMETs are expected tonight but will monitor for lower ceilings, visibilities and extensive mountain obscuration on the Big Island.

Marine

A high pressure ridge north of the Hawaiian Islands will maintain fresh to locally strong trades into Thursday before weakening as a cold front approaches from the north. A Small Craft Advisory (SCA) remains in effect for the typical windier zones around the Big Island and Maui, but the north zones near Kauai and Oahu have been dropped as seas have remained below the threshold. Trade winds will gradually decline from Thursday through Friday as the cold front approaches and then weakens and potentially stalls over the northwestern and central waters from Saturday to Sunday. Stronger northeast winds will blow across waters north of the front, with moderate easterly winds south of the frontal boundary.
A gale force low that passed far north of the state on Monday has produced a moderate to large medium period north-northwest (340-350 degree) swell that will move across the Hawaiian waters through Thursday. This swell seems to be underperforming, with most of the energy likely passing to the northeast of the state, as evidenced by the observations at buoy 51000. Will keep the current High Surf Advisory (HSA) in effect for now in case the swell builds later this afternoon or evening, but it might need to be cancelled early. This swell should peak this evening and then gradually fade heading into Friday. In the longer range forecast, a deep low pressure system is expected to develop to our north and northeast from Friday into Saturday. This low will likely generate a large north-northeast (010-020 degree) swell late this weekend, easily exceeding HSA thresholds. Due to the swell angle, heavy surges will be possible along north facing harbors such as Kahului and Hilo on Sunday.
South facing shores will remain small throughout this week. A small long-period south-southwest swell will boost south shore surf heights from Friday into the weekend, along with a larger out of season south swell possible by early next week. Surf for east facing shores should be rough and choppy tomorrow with the locally breezy trade winds and could also see a little bit of north wrap from the medium period north-northwest swell.
Peak monthly tides combined with water levels that are running higher than predicted will lead to minor flooding along the shoreline and in low-lying coastal areas. The greatest chance for coastal flooding will occur during the daily peak high tide during the early morning hours, and along north facing shores exposed to the large north-northwest swell.

Fire weather

Winds and relative humidity values are expected to remain below critical fire weather thresholds into the weekend. The inversion will be between 6,500 to 7,500 feet tonight as a mid level ridge builds overhead, further stabilizing the atmosphere and limiting vertical mixing.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Thursday for Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala, Big Island East, Big Island North.
Small Craft Advisory until 6 AM HST Thursday for Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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