West Kaua’i

Tonight: Breezy. Partly cloudy with isolated showers. Lows around 69 near the shore to around 57 above 3000 feet. East winds 10 to 20 mph decreasing to up to 20 mph after midnight. Gusts up to 40 mph. Chance of rain 20 percent.

Tuesday: Breezy. Mostly sunny with isolated showers. Highs around 81 near the shore to around 70 above 3000 feet. East winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 20 percent.

Tuesday Night: Breezy. Partly cloudy with isolated showers. Lows around 69 near the shore to around 57 above 3000 feet. East winds 10 to 20 mph shifting to the northeast up to 20 mph after midnight. Gusts up to 40 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 63 to 71. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs around 78. East winds 20 to 25 mph. Chance of rain 50 percent.

Tuesday Night: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows 63 to 71. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 55 to 64 in the valleys to around 51 above 4000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Tuesday: Partly sunny. Windy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 69 to 75 in the valleys to around 61 above 4000 feet. East winds 10 to 30 mph. Chance of rain 70 percent.

Tuesday Night: Mostly cloudy. Windy. Scattered showers in the evening, then numerous showers after midnight. Lows 55 to 64 in the valleys to around 51 above 4000 feet. East winds 10 to 30 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 60 to 70. East winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 71 to 81. East winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday Night: Breezy. Mostly cloudy with scattered showers. Lows 60 to 70. East winds 10 to 20 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 56 to 72. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 70 to 80. East winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday Night: Breezy. Mostly cloudy with scattered showers. Lows 56 to 72. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A band of moisture associated with an old front will keep windward Big Island rather wet tonight, while improving conditions are expected on Maui. Elsewhere, typical trade wind showers will prevail. Fairly typical but windy trade wind weather is then expected Tuesday through Wednesday. The trades will ease a bit and gradually shift more east-southeasterly Thursday and Friday, with showers favoring windward areas at night, and a few more showers possible over interior and leeward areas Friday afternoon. A hybrid trade wind pattern should then take hold over the weekend into early next week, with showers favoring windward areas at night and interior and leeward sections of the islands each afternoon.

Discussion

Currently at the surface, a 1031 mb high is centered around 800 miles north of Honolulu, while the remnants of an old front are moving through the Maui and the Big Island. The gradient locally is producing breezy trade winds across the state this afternoon. Visible satellite imagery shows partly to mostly cloudy conditions, with cloud coverage the highest in windward and mauka locales as well as leeward Big Island. Radar imagery shows numerous to widespread shower activity affecting windward sections of Maui and the Big Island, isolated to scattered showers over windward areas from Kauai to Molokai, and scattered showers over leeward Big Island. Main short term focus revolves around rain trends and the need for a Wind Advisory Tuesday and Tuesday night.
High pressure north-northeast of the state will merge with a new building high to the north of the islands late tonight, with this high then slowly settling southward Tuesday through Wednesday. Meanwhile, the remnants of an old front will sink southward through Maui and the Big Island tonight, with inversion heights dropping quickly in its wake. This is expected to increase the trades, with windy conditions developing early Tuesday and continuing through Wednesday. A Wind Advisory has been issued for the typically windier locations across Maui County and the Big Island from 6 AM Tuesday through 6 AM Wednesday.
The high will gradually weaken as it remains anchored northeast of the islands Thursday and Friday, while a storm system develops west of the state. Breezy trades will continue across the area Thursday, with an easing expected particularly over the western islands on Friday as the directions shifts more east- southeasterly. The storm system will shift closer to the state over the weekend into early next week. The winds will shift more southeasterly in response, with land and sea breezes becoming more common over the western islands, while moderate trades persist over the eastern end of the state.
As for the remaining forecast details, a band of deeper moisture associated with an old front will push southward through Maui and the Big Island tonight. Rather wet conditions are expected over the Big Island, with improving conditions expected on Tuesday, while conditions should improve on Maui this evening. Otherwise, we should get back into a more uniformly distributed trade wind shower pattern tonight through Thursday, with showers favoring windward and mauka areas and a stray shower reaching leeward areas from time to time. A trough aloft appears to work northward across the islands on Friday, which could bring an increase in windward showers and a few more leeward and interior showers in the afternoon. A hybrid trade wind pattern should then take hold over the weekend into early next week, with showers favoring windward areas at night and interior and leeward sections each afternoon.

Aviation

A drier air mass has filled in behind the remnants of an old front. Wet and breezy trade wind weather will bring periods of MVFR conditions in ceilings and visibility mainly over Maui and the Big Island through tonight. Trade winds will ramp up to breezy to locally strong tonight through Tuesday.
AIRMET Sierra for mountain obscuration is currently in effect for north and east facing slopes of Maui and the Big Island as the remnant cloud band continues to drift southward. Conditions are expected to improve this evening across Maui and late tonight on the Big Island.
AIRMET Tango remains in effect for moderate low level turbulence over and downwind of island terrain. This AIRMET is expected to continue over the next several days.

Marine

Another strong high building far north of the state will strengthen the trade winds tonight into Tuesday with strong to gale force winds expected by Tuesday. Gale Warnings are in effect starting Tuesday morning for Alenuihaha and Pailolo Channels and Maalaea Bay through Tuesday night. A Small Craft Advisory is in effect for all of the remaining Hawaiian waters. Winds may hold at gale force speeds through Wednesday. Trade winds should begin to weaken slightly towards the end of the week as a trough develops west of the state, which will cause the trade winds to veer toward the east-southeast by Friday. Fresh to strong east to east-southeast winds will likely persist through the weekend.
The current small north-northwest swell (340 degree) will continue to steadily decline and fade out on Tuesday. A moderate long-period north-northwest (330 degree) swell will arrive Tuesday evening and peak on Wednesday likely below advisory thresholds. A slightly larger long-period west-northwest to northwest swell (300 to 320 degree) is expected to fill in Thursday night and peak on Friday. This swell could briefly approach advisory thresholds for select north and west facing shores on Friday and gradually decline over the weekend.
Rough surf will continue along east facing shores through the week in response to the persistent strong trade winds over and upstream of the islands. Surf will near High Surf Advisory criteria Tuesday through midweek as trades peak in strength. Surf along south-facing shores will remain small, but a small bump out of the south-southwest is expected by Wednesday.

HFO Watches/Warnings/Advisories

Wind Advisory from 6 AM Tuesday to 6 AM HST Wednesday for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kohala, Lanai Windward, Lanai Leeward, Maui Central Valley North, Maui Central Valley South, South Haleakala, Big Island South, Big Island Southeast, Big Island North.
Small Craft Advisory until 6 AM HST Wednesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 AM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel.
Gale Warning from 6 AM Tuesday to 6 AM HST Wednesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel.

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