West Kaua’i

Rest Of Tonight: Partly cloudy. Isolated showers and thunderstorms in the evening, then isolated showers after midnight. Lows 65 to 71 near the shore to around 58 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny in the morning then becoming partly sunny. Breezy. Isolated showers. Highs 81 to 86 near the shore to around 70 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Wednesday Night: Breezy. Mostly cloudy with isolated showers. Lows 65 to 70 near the shore to around 58 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

Rest Of Tonight: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Lows around 68. East winds 10 to 15 mph. Chance of rain 40 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs 76 to 84. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Wednesday Night: Breezy. Cloudy with scattered showers. Lows around 68. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Kaua’i Mountains

Rest Of Tonight: Mostly cloudy. Numerous showers and isolated thunderstorms in the evening, then numerous showers after midnight. Lows 61 to 67 in the valleys to around 56 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Wednesday: Breezy. Mostly cloudy with numerous showers. Highs 70 to 80 in the valleys to around 61 above 4000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 70 percent.

Wednesday Night: Cloudy with numerous showers. Lows 61 to 66 in the valleys to around 56 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Rest Of Tonight: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Lows 62 to 69. Southeast winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs 75 to 82. East winds up to 20 mph. Chance of rain 50 percent.

Wednesday Night: Cloudy with scattered showers. Lows 62 to 69. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Rest Of Tonight: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Lows 63 to 72. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy with scattered showers. Highs 71 to 82. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Cloudy with scattered showers. Lows 62 to 72. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Trades will build tonight and bring enhanced windward showers through the second half of the week due to an upper trough moving across the area. Conditions are expected to stabilize Saturday. A weak cold front will approach from the west Sunday, reach Kauai Monday and stall near Big Island midweek.

Discussion

An upper low to the west of Hawaii will weaken and broaden as it moves over the islands over the next several days. At the surface, high pressure far to the northeast will drive a slightly modified east southeast flow through the early evening that will strengthen to moderate to fresh trades by morning and continue through the second half of the week. Radar shows heavy showers briefly formed due to the daytime heating and instability over Kauai, Oahu and leeward Big Island this afternoon and are expected to fade through sunset.
Easterly trades will begin to focus more of the clouds and showers moving in from upstream across windward and mauka areas beginning tonight. Some enhancement of the trade wind showers will be possible as the aforementioned upper trough moves eastward across the state through the end of the week. Conditions should dry and stabilize by Saturday. On Sunday, winds will weaken and veer southeasterly in response to an approaching cold front that should reach Kauai Sunday night or Monday. GFS coming into line with the ECMWF in the long range showing the front stalling near or past the Big Island midweek.

Aviation

Light to moderate trade winds will gradually fill in from east to west tonight, and could become locally breezy tomorrow through midweek. Stability will marginally increase as drier air moves in, however upper level conditions could still be unstable enough to allow some of the trade wind showers to be on the heavier side. Overall clouds and showers will favor windward and mauka locations throughout the forecast period and VFR conditions should prevail. The exception being the Big Island windward areas, where enhanced moisture could move in tomorrow morning and bring MVFR ceilings and visibilities.
AIRMET Tango is in effect for moderate upper level turbulence over and west of Maui due to an upper level jet. This will likely linger through tomorrow. AIRMET Sierra is in effect for mountain obscuration over Kauai due to some leeward cloud buildups. Conditions should improve after sunset.

Marine

A surface trough, located approximately 525 nautical miles west of Kauai, is helping to maintain gentle easterlies over the western half of the state, while moderate to fresh east- southeast winds continue over the eastern half. An upper low near the same location will weaken and wash out through the middle of the week as surface high pressure north of the state becomes the dominant Central Pacific feature. Easterly trades will strengthen to moderate to fresh speeds tonight. A Small Craft Advisory has been issued for the typically windy waters around Maui County and the Big Island through Thursday afternoon. Winds will gradually weaken and shift southeasterly into the weekend, becoming light and variable statewide by Sunday as a front approaches the state from the northwest.
A series of small, medium-period northwest (310-320 degree) swells will pass through tonight through Saturday. These swells will maintain solid head-high surf along most north-facing shores and waist to head high surf along the better-exposed west shores. A significant northwest swell may reach the islands early next week.
East shore surf will likely pick up a bit through the middle of the week as easterlies increase over and upstream of the state. South shore surf will stay around the seasonal average, as a couple of small, long-period south swells move through the local waters this week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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