West Kaua’i

Rest Of Tonight: Mostly cloudy with isolated showers. Lows around 74 near the shore to around 64 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers in the morning. Highs 85 to 92 near the shore to around 77 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 74 near the shore to around 63 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Rest Of Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 72 to 78. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 79 to 90. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 72 to 77. Northeast winds around 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Rest Of Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows around 70 in the valleys to around 62 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Breezy. Mostly cloudy with scattered showers. Highs 74 to 82 in the valleys to around 67 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows around 69 in the valleys to around 61 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Rest Of Tonight: Mostly cloudy with scattered showers. Lows 65 to 75. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 71 to 86. East winds 10 to 15 mph. Chance of rain 40 percent.

Wednesday Night: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 65 to 75. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Rest Of Tonight: Mostly cloudy with scattered showers. Lows 68 to 78. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy with scattered showers. Highs 77 to 85. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 68 to 77. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will continue through the weekend. Bands of low clouds and showers will be carried in on the trades, focused primarily over windward and mauka areas during the overnight and early morning hours. An enhanced area of moisture is expected to reach the islands tonight through Wednesday, bringing more widespread showers. Humidity levels will rise, bringing muggier conditions across the island chain through the middle of this week. Additional areas of increased low level moisture are possible this weekend.

Discussion

High pressure will remain far north of the state (centered around 40N) for the coming week as it slowly drifts west. Moderate to breezy trade winds will continue through the period, with showers mainly windward and mauka, and more numerous at night. A trough appears on satellite imagery passing north of the islands this afternoon. Upstream (east) of the islands, an enhanced cluster of cumulus clouds, indicating increased rain shower activity, has decreased significantly in intensity since this morning. These features will track westward across the islands tonight through Wednesday, bringing increased shower activity to windward and mauka areas, and increasing the chance for noticeable spillover to leeward areas. Brief heavy rain is possible, but the risk for flooding is low.
Surface dewpoints will increase into the lower 70s by tonight as this pocket of moisture arrives, but the more well- defined trough will skirt north of the islands, meaning the most significant increase in moisture/rainfall is expected to miss the islands. As a result, rain shower coverage and intensity has actually been somewhat decreased in the forecast. Drier (more seasonal) conditions are then expected from Wednesday night into the weekend as dew points drop back into the mid to upper 60s. There is some potential for low-level moisture to increase again this weekend. Temperatures aloft remain quite warm, at -5C or warmer, which means there will be no additional upper-level support for very heavy precipitation or thunderstorms.

Aviation

Moderate to locally breezy trade winds continue through the forecast period. An influx of moisture associated with a trough will bring increased shower activity tonight into Wednesday for windward and mountain areas. Afternoon showers over kona slopes of the Big Island are also possible. Expect primarily MVFR conditions within showers, and VFR elsewhere.
No AIRMET's are currently in effect, but AIRMET Sierra will likely be needed for mountain obscurations tonight when showers start impacting windward and mountain areas.

Marine

Surface high pressure far north northeast of the islands will slowly drift west through the forecast period keeping moderate to locally strong trade winds through Wednesday before declining slightly through the rest of the forecast period. The Small Craft Advisory (SCA) is in effect through Wednesday afternoon for the windier waters and channels around Maui County and the Big Island and may be extended through Wednesday night.
The small medium period south swell will keep surf heights elevated along south facing shores this afternoon before declining Wednesday. A series of small medium to long period south southwesterly swells are expected Thursday through the weekend. Surf along east facing shores will remain rough and choppy and increase Wednesday as trade winds increase. Surf along north facing shores will remain flat to tiny through the forecast period.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov