West Kaua’i

Tonight: Mostly clear. Isolated showers in the evening. Lows around 75 near the shore to around 66 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Sunny. Isolated showers in the afternoon. Highs 87 to 93 near the shore to around 80 above 3000 feet. North winds up to 10 mph shifting to the southwest in the afternoon. Chance of rain 20 percent.

Wednesday Night: Mostly clear with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 77 near the shore to around 67 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 72 to 78. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 91. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Wednesday Night: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with numerous showers after midnight. Locally heavy rainfall possible after midnight. Lows 73 to 78. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 71 in the valleys to around 63 above 4000 feet. East winds up to 10 mph. Chance of rain 60 percent.

Wednesday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 77 to 84 in the valleys to around 76 above 4000 feet. East winds up to 15 mph. Chance of rain 60 percent.

Wednesday Night: Mostly cloudy. Breezy. Scattered showers in the evening, then occasional showers after midnight. Locally heavy rainfall possible after midnight. Lows around 72 in the valleys to around 64 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 90 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 67 to 76. Southeast winds up to 10 mph. Chance of rain 50 percent.

Wednesday: Mostly sunny with scattered showers. Highs 73 to 89. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday Night: Partly cloudy with scattered showers in the evening, then mostly cloudy with numerous showers after midnight. Locally heavy rainfall possible after midnight. Lows 68 to 77. East winds up to 15 mph. Chance of rain 70 percent.

East Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 69 to 77. North winds up to 10 mph. Chance of rain 60 percent.

Wednesday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 80 to 87. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 60 percent.

Wednesday Night: Mostly cloudy. Scattered showers in the evening, then occasional showers after midnight. Locally heavy rainfall possible after midnight. Lows 70 to 78. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Detailed Forecast

Synopsis

Moderate trades will strengthen to breezy levels Wednesday and hold through the forecast period. Moisture will continue to fill in across the state from east to west tonight into Friday increasing chances of showers mainly for windward and mauka areas. Chances of heavy rain, isolated thunderstorms and flood potential will increase Thursday into Friday as an upper level disturbance moves overhead. Drier air will move back in this weekend as trades continue. Moisture from the remnants of Tropical Depression 15-E may bring another round of enhanced trade showers early next week.

Discussion

Radar and satellite show light to moderate showers over mauka areas of Oahu and portions of Maui County. A cluster of moderate showers remains upstream of Kauai. The highest rainfall totals through the day were observed at West Wailuaiki with 1 inch of rainfall in the past 3 hours. Oahu windward areas received between .20 to .40 inches in the past 3 hours. Elsewhere mainly light showers were focused along windward and mauka areas. Gentle to moderate trades were observed across the state.
A large area of enhanced moisture as seen in the CIMSS precipitable water imagery is still making its way across the state from east to west. Thus expect and increase in scattered light to moderate showers tonight that will focus primarily along windward and mauka areas. Although upper level ridging should limit the potential of heavy showers, brief heavy showers cannot be ruled out overnight especially for Kauai as the cluster of enhanced showers moves over the complex terrain.
An upper level trough will sink down over the state Wednesday afternoon and evening just as the deepest surge of moisture from Norbert begins to move across the state. This will result in a sharp increase in moderate to heavy showers from late Wednesday night through early Friday. Instability will be sufficient for an isolated thunderstorm as well. A flood watch may be needed for Thursday but could be issued as early as Wednesday.
Moisture will decrease late Friday through the weekend. Latest guidance remains on track, showing another area of increasing moisture (from the remnants of tropical depression 15-E) will likely move into the area Monday or Tuesday next week. The GFS shows better upper level support that could enhance the trade showers while ECMWF shows mid level ridging that could help limit heavy shower potential. Will continue to monitor all available guidance to determine exact impacts with future updates.

Aviation

The forecast is on track as the trade winds continue to gradually strengthen and become locally breezy this afternoon into the evening. Isolated to scattered showers have slowly been passing by the islands, while we've seen an increase in cloud and shower activity on the windward sides of the island. MVFR conditions will be possible in passing showers. Otherwise, VFR conditions will prevail. A similar set up is expected for Wednesday, with wetter weather returning on Thursday.
AIRMET Sierra is in effect for tempo mountain obscuration for windward areas of the Big Island through Oahu, including Lanai. Conditions are expected to improve or end around 0400Z.

Marine

Prominent low pressure south of the islands maintains fresh trades from tomorrow onward. A Small Craft Advisory will be needed for Wednesday and potentially beyond. Remnants of TC Norbert will bring isolated thunderstorms to area waters Thursday night through Friday night.
Long period energy out of the S to SW fills in during the latter half of the week supporting building surf for S shores. Surf is initially small through Wednesday but will trend upward toward the High Surf Advisory threshold by this weekend. Surf along E shores will modestly increase in response to building trades and a brief medium period E swell emanating from former TC Norbert. N shores stay flat to tiny.

Fire weather

Fire weather risk should remain low through the remainder of the week due to moderate winds and increased relative humidity and moisture from the remnants of Norbert. Showers will dramatically increase late Wednesday into early Friday. Inversion heights from Maui to the Big Island will be elevated around 7,500 to 8,500 ft.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov