West Kaua’i

Tonight: Mostly clear with isolated showers. Lows around 66 near the shore to around 56 above 3000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers. Highs 79 to 85 near the shore to around 72 above 3000 feet. Light winds becoming south up to 10 mph in the afternoon. Chance of rain 20 percent.

Wednesday Night: Partly cloudy with isolated showers. Lows around 66 near the shore to around 56 above 3000 feet. Light winds becoming southeast up to 10 mph after midnight. Chance of rain 20 percent.

South Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 66. Light winds. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers. Highs 78 to 85. Northeast winds around 10 mph shifting to the southeast up to 10 mph in the afternoon. Chance of rain 20 percent.

Wednesday Night: Partly cloudy with isolated showers. Lows around 66. Light winds. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Partly cloudy. Lows 57 to 66 in the valleys to around 55 above 4000 feet. Light winds.

Wednesday: Mostly sunny. Scattered showers in the afternoon. Highs 72 to 79 in the valleys to around 64 above 4000 feet. Light winds. Chance of rain 30 percent.

Wednesday Night: Partly cloudy. Isolated showers in the evening. Lows 56 to 66 in the valleys to around 54 above 4000 feet. Light winds becoming southwest up to 10 mph after midnight. Chance of rain 20 percent.

North Kaua’i

Tonight: Mostly clear. Lows 60 to 67. Light winds.

Wednesday: Mostly sunny. Scattered showers in the afternoon. Highs 74 to 81. Southeast winds up to 10 mph. Chance of rain 30 percent.

Wednesday Night: Partly cloudy. Isolated showers in the evening. Lows 60 to 67. Light winds becoming south up to 10 mph after midnight. Chance of rain 20 percent.

East Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 59 to 70. Light winds. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers. Highs 73 to 83. Northeast winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 20 percent.

Wednesday Night: Partly cloudy with isolated showers. Lows 59 to 69. Light winds becoming southwest around 10 mph after midnight. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Rather dry and stable weather will persist through Thursday, as winds gradually shift around to the south. A few showers will remain possible along windward slopes and coasts at night and over island interiors each afternoon. Showers will slowly increase in coverage and intensity over the western islands Thursday night into Friday as a weakening front moves in from the west and stalls out near Kauai. A ridge building north of the state should bring a return to drier conditions and light to moderate trades Friday night and Saturday, although showery weather will develop across windward Big Island as some deeper moisture moves in from the east. A new front will strengthen south to southwest winds and bring unsettled weather, and potentially heavy showers, into the area Sunday through early next week.

Discussion

Currently at the surface, a 1026 mb high is centered around 1500 miles east-northeast of Honolulu, with a ridge extending westward to a position around 125 miles north of Kauai. Land breezes are present or developing across the vast majority of the state, with some unsheltered sections over the eastern islands seeing light to locally moderate east-southeasterly trades. Infrared satellite imagery shows decreasing cloud cover across the state, with cloud coverage the greatest over leeward sections of the Big Island. Radar imagery shows very little shower activity, with nothing more than a few light showers affecting windward slopes. Main short term focus revolves around the incoming front at the end of the work week.
The ridge north of the islands will keep land and sea breezes dominant across much of the state through Wednesday night, with light to moderate east-southeasterly trades holding on in the unsheltered sections over the eastern islands. Winds will pick up out of the south on Thursday as a front approaches the area, reaching moderate speeds by late in the day over the western islands, while a more southeast component and lighter speeds hold over the eastern end of the state. The front will fizzle out over or near Kauai late Thursday night and Friday, with winds lightening up across the state and land/sea breezes becoming dominant. The front or its remnants will lift northward Friday night and Saturday, allowing ridging to the northeast to become more dominant and bring a return of light of moderate trade winds. The trades won't last long, as yet another approaching front will shift winds southerly at moderate speeds for Sunday, followed by easing winds and land/sea breezes on Monday as the front dissipates over the central islands. High pressure building rapidly eastward to the north of the state may re-establish trades again next Tuesday.
As for the remaining weather details, dry and stable weather will continue through Thursday. A few showers will remain possible over windward slopes and coasts at night, particularly over the eastern end of the state, with a shower or two possible over the interior of all islands each afternoon. The boundary layer should begin to moisten up Thursday night, bringing a bit more shower activity northward in the southerly flow. These showers will favor south facing slopes and coasts mainly over the western islands. As deeper moisture associated with the decaying front arrives on Friday, we should see shower coverage and intensity pick up over the western islands, particularly on Kauai where a few downpours will be possible. The eastern end of the state will remain rather dry, with nothing more than a few isolated showers possible during the afternoon hours.
Scattered showers may hold on into the evening hours Friday over Kauai, before drier conditions move in after midnight. Elsewhere, mostly dry conditions will prevail, with the exception of windward Big Island where some deeper moisture moving in from the east will bring an increase in shower coverage and intensity through the night. Showery weather looks to hold on over windward Big Island on Saturday, while mostly dry weather prevails over the smaller islands. The next front will begin to draw some of the deeper moisture around the Big Island northward into the smaller islands Saturday night, increasing showers over south facing slopes and coasts. Some unsettled weather then appears on track to affect the state in association with the front Sunday through Monday, with some heavier showers and even a few rumbles of thunder not out of the question. A trade wind pattern appears to return next Tuesday, but lingering moisture and instability may keep showers a bit more robust than normal.

Aviation

Light to moderate ESE winds will persist through tomorrow with a relatively dry and stable airmass overhead. Winds will be light enough to allow for some sea/land breezes. Low cigs and brief SHRA can be exp over interior and leeward areas. MVFR conds are possible in SHRA but otherwise VFR conds exp to prevail.
No AIRMETs are in effect.

Marine

A surface ridge located roughly 100 nautical miles north of Kauai will maintain gentle southeast or variable winds over the western half of the island chain and moderate east to southeast winds around the Big Island and Maui through Wednesday. An approaching front will push the ridge over the islands veering winds to more of southeast to south direction and strengthening to moderate speeds for the western half of the state on Thursday. The front will stall and weaken near Kauai on Friday as high pressure approaches from the northwest, leading to a decrease in winds and eventually bringing a return of gentle trades. As the high builds and rapidly moves off to the northeast, easterly trade winds will strengthen on Saturday, with Small Craft Advisory (SCA) conditions possible over the typically windy areas. Winds will decrease and shift out of the south as another front approaches on Sunday.
A series of west-northwest swells will produce elevated surf into the weekend. Offshore NOAA buoy 51001 measured the swell at 9 to 11 ft at 15 seconds since this afternoon, and is expected to receive a reinforcing boost late tonight that could keep surf elevated through Wednesday. A High Surf Warning remains in effect for north and west facing shores of Kauai and Niihau and for north facing shores of Oahu, Molokai, and Maui. Due to the westerly component of the swell (290-300 degrees), there will be significant shadowing produced by the islands, and the west facing shores of Oahu and Molokai remain under a High Surf Advisory (HSA). These headlines only run through early morning Wednesday, and will continue to monitor latest observations to determine if an extension is needed, but at the least expect advisory level surf to prevail Wednesday into Thursday. A HSA remains in effect for west facing shores of the Big Island from midnight through Wednesday afternoon, and due to the significant westerly component of the swell, we will continue monitor buoys overnight for the potential of larger swell impacting the Big Island. A SCA remains in effect for seas of 10 ft or more, mainly in swell, around Kauai and north of Oahu. Surf will fall below advisory levels Thursday, followed by another large pulse of west-northwest swell on Friday and Saturday.
Surf along east and south facing shores will remain small through the week, though a modest uptick in waves on the south shore is possible later Wednesday into the weekend.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 AM HST Wednesday for Niihau, Kauai Leeward, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Maui Central Valley North, Windward Haleakala.
High Surf Advisory until 6 AM HST Wednesday for Waianae Coast, Molokai West.
High Surf Advisory from midnight tonight to 6 PM HST Wednesday for Kona, Kohala.
Small Craft Advisory until 6 AM HST Wednesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters.

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