West Kaua’i

Tonight: Cloudy and breezy. Isolated showers in the evening, then scattered showers after midnight. Lows 69 to 74 near the shore to around 62 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Mostly cloudy with scattered showers. Highs 82 to 88 near the shore to around 74 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy. Scattered showers in the evening. Lows 68 to 73 near the shore to around 61 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 40 percent.

South Kaua’i

Tonight: Cloudy and breezy. Scattered showers in the evening, then numerous showers after midnight. Lows around 73. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Friday: Breezy. Mostly cloudy with numerous showers. Highs 78 to 86. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Friday Night: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 71. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Breezy. Cloudy with frequent showers. Lows 64 to 69 in the valleys to around 59 above 4000 feet. East winds 10 to 25 mph decreasing to up to 20 mph after midnight. Chance of rain 90 percent.

Friday: Cloudy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 72 to 80 in the valleys to around 64 above 4000 feet. East winds up to 15 mph. Chance of rain 90 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 62 to 69 in the valleys to around 58 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Cloudy and breezy. Numerous showers in the evening, then frequent showers after midnight. Lows 65 to 73. East winds up to 20 mph. Chance of rain 90 percent.

Friday: Mostly cloudy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 75 to 85. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 90 percent.

Friday Night: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 63 to 72. East winds around 10 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows 64 to 76. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 90 percent.

Friday: Mostly cloudy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 71 to 83. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 90 percent.

Friday Night: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 63 to 75. East winds around 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A breezy and somewhat wet trade wind flow will prevail into Thursday morning, followed by a gradual decline in winds and shower activity late Friday. Trade winds will decline to light to moderate strength as high clouds thin during the weekend, and while showers will favor windward slopes, a few afternoons shower will be possible over leeward terrain on Saturday. A stable moderate trade wind flow is expected Sunday through early next week.

Discussion

Breezy trade winds persist this afternoon, and a band of shower- bearing low clouds can be observed just off the windward coasts of most islands underneath a shroud of layered high clouds. A 1031 mb surface high is centered roughly 1300 miles northeast of Hawaii is driving the gusty trades, while a persistent upper level trough centered just to the west and northwest continues to send layered high clouds over the state. Shower activity has been subdued this afternoon over all islands except windward Kauai, as the low level flow has dried slightly ahead of a band of moisture lingering just east of the islands.
Shower activity is expected to pick up tonight and linger into Friday morning as the band of moisture is carried in on the gusty trade wind flow. The bulk of the rainfall will be focused on windward slopes, but periods of showers are expected over leeward areas from Kauai to Maui, as the breezy trades begin a slow decline. The nearby upper level trough will continue to send layered high clouds over the state, and a weak mid level ridge noted on this afternoon's soundings will likely be eroded as the band moves through, opening the possibility for a few briefly heavy showers tonight. A few of those showers may reach the high summits of the Big Island as rain, though there is a small possibility of some ice briefly developing late tonight.
Trade winds will decline into the light to moderate range late Friday and Saturday as shower activity decreases. A shortwave aloft will pick up the upper level trough that has been sitting near the islands and push it overhead on Saturday. It does not appear that it will produce a great deal of instability, but under the weakened trade wind flow, it could trigger a few afternoon showers over leeward terrain in the afternoon.
Light to moderate trade winds will hold Sunday through early next week as upper level ridging moves overhead and produces a rather stable pattern of mainly windward showers. Trades may become disrupted during the middle of next week, but the spread in model guidance remains significant, keeping uncertainty high.

Aviation

VFR conditions prevail through most areas across the state with occasional MVFR due to CLD and SHRA over windward and mountainous areas. Mid to high clouds will continue to move from the southwest to northeast across the state. Breezy trade winds continue through the evening, but will begin to gradually weaken tonight.
AIRMET Tango in effect due to low level turb lee of mtn. This is expected to continue at least through the evening.
AIRMET Sierra is in effect for tempo mountain obscuration over Kauai N thru SE sections due to CLD and SHRA. This is expected to continue into tonight and could be expanded at least to Oahu due to showers upstream.
AIRMET Zulu is not in effect, however there could be TEMPO light icing associated with the mid level CLD from Kauai to Maui in layer 150-FL230.

Marine

High pressure northeast of Hawaii will weaken and track eastward over the next couple of days as a front moves across the North Pacific. As this occurs, easterly trades across the Hawaiian coastal waters will gradually weaken. A Small Craft Advisory (SCA) remains in effect for most Hawaiian waters, though it has been dropped for waters surrounding Kauai and for leeward waters of Oahu and Maui County as both wind speeds and seas gradually decline. Further reductions in the area of the SCA are anticipated by early Friday morning.
A new area of high pressure will become established north of the islands this weekend, though trades will remain in the moderate to fresh range this weekend through the first half of next week.
The current, medium period northwest swell peaked earlier today and will continue to decline tonight into early Friday. Based on observations and buoy data, surf along north and west facing shores has fallen below advisory levels, and the High Surf Advisory was allowed to expire. Another moderate, medium period, northwest swell (310-330 degrees) is forecast to arrive Saturday into Sunday, and could once again produce surf at or near advisory levels along north and west facing shores. Looking ahead to the middle of next week, a large, long period, northwest (310-330 degree) swell has the potential bring advisory or even warning level surf along north and west facing shores.
East shore surf will decline Friday into this weekend as trades weaken over and upstream of the islands.
Small surf is expected along south facing shores for the next several days.

Fire weather

Critical fire weather conditions are not expected through the week. A breezy and somewhat wet trade wind flow will keep humidity elevated into Friday, with rainfall and trade winds decreasing late Friday and Saturday. Light to moderate trade winds and rather stable conditions will prevail Sunday through early next week.

HFO Watches/Warnings/Advisories

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