West Kaua’i

Tonight: Partly cloudy. Lows around 69 near the shore to around 60 above 3000 feet. East winds up to 10 mph.

Friday: Mostly sunny in the morning then becoming mostly cloudy. Isolated showers. Highs 80 to 85 near the shore to around 71 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Friday Night: Breezy. Cloudy with isolated showers. Lows around 69 near the shore to around 60 above 3000 feet. East winds up to 20 mph increasing to 10 to 20 mph after midnight. Chance of rain 20 percent.

South Kaua’i

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 69. East winds 10 to 15 mph. Chance of rain 30 percent.

Friday: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 77 to 84. East winds 10 to 15 mph. Chance of rain 30 percent.

Friday Night: Cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 69. East winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Partly cloudy with isolated showers. Lows 61 to 68 in the valleys to around 58 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Friday: Mostly cloudy with scattered showers. Highs 72 to 79 in the valleys to around 64 above 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Breezy. Cloudy with scattered showers. Lows 62 to 68 in the valleys to around 58 above 4000 feet. East winds up to 20 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy. Isolated showers in the evening. Lows 62 to 71. Southeast winds up to 10 mph. Chance of rain 20 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 74 to 83. Southeast winds up to 15 mph. Chance of rain 20 percent.

Friday Night: Mostly cloudy with isolated showers. Lows 62 to 71. East winds up to 15 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 63 to 73. East winds up to 15 mph. Chance of rain 30 percent.

Friday: Partly sunny with scattered showers. Highs 71 to 82. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Cloudy with scattered showers. Lows 64 to 73. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Quiet weather characterized by stable ESE winds prevails into Monday. Winds then veer to the south and draw north deep tropical moisture setting the stage for wet weather next week.

Discussion

Dry and stable breezy ESE winds continue into early next week. Blocking of the flow by the larger islands will facilitate afternoon sea breeze development over the western end of the state that will favor interior clodus clouds and isolated showers each afternoon for the smaller islands. Developing land breezes bring clearing overnight.
Attention then turns to Monday night through the remainder of next week which may be particularly active. By late this week, the tail end of a cold front lifting into the Gulf of Alaska is modeled to settle immediately west of the islands as broad ESE low-level flow persists. Low pressure nestled within the left exit of digging Pacific jet will absorb this remnant frontal band and usher it east into the forecast area as early as Monday night, most likely in the vicinity of Kauai. Impressive dynamics aloft will develop the front vertically allowing heavy showers to organize as they increase in coverage and intensity. At the same time, deep southerly flow transports PWATs of at least 1.75″ into the forecast area deepening the warm cloud layer, providing additional moisture for heavy rain, and enveloping the forecast area in a broad corridor of weak isentropic ascent that will likely produce at least a few pockets of heavy rain well in advance of the front. Aggregate low pressure remains established NW of the state for the entirety of next week with multiple embedded shortwaves providing periods of stronger forcing as the frontal band slowly advances east. On this much, consensus is very strong among the global guidance. Clarity on timing for each island and magnitude of rainfall will come during the next few days as the event draws nearer and especially once it enters the hi-res window. Regardless, a long- lived flash flood threat is poised to manifest over part or all of the islands for essentially all of next week.

Aviation

East-southeast moderate surface winds will continue tonight and Friday. There will be areas of MVFR in low clouds and showers, mainly on east and south sections of Kauai and Oahu. VFR in most locations.
AIRMET Sierra currently in effect for E through S Kauai and Oahu, and this is expected to continue into tonight.

Marine

Fresh to locally strong east-southeast trade winds will continue tonight into Friday as high pressure remains centered far northeast of the main Hawaiian Islands. Therefore, a Small Craft Advisory (SCA) remains in effect through Friday evening for the typically windy channels and waters of Maui County and the Big Island. This general wind pattern is likely to hold through the weekend. A large low pressure system approaching from the west this weekend will stall northwest of the islands beginning early next week. Winds will veer more southerly in response to the low's cold front making a close approach, or even entering the northwest offshore waters, by mid-week. Locally strong southerly winds will be possible depending on how close the cold front gets to the islands.
Surf along north and west-facing shores will remain small as a series of small, long- to medium-period northwest swells reach the Hawaiian Islands over the next week or so. Forerunners of the next small northwest swell have been observed at northwest Hawaii buoy 51001 today, and should arrive in the islands this evening. This small northwest swell is expected to provide a small bump in surf along north and west-facing shores. It will be followed by another small northwest swell that will maintain the small surf through the weekend. A compact storm-force low currently just off the coast of Japan will likely produce another small west- northwest swell early next week.
Choppy east shore surf will remain near seasonal averages as east-southeasterly trade winds vary minimally over the next few days, with a chance for a slight increase over the weekend. Surf along east-facing shores will then decline early next week as winds veer more southerly.
Surf along south-facing shores will remain small through the weekend, but is then expected to increase and become choppier with the shift to a more southerly wind direction early next week. A small, long-period south swell is also possible around Tuesday of next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Friday for Maui County Windward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov