West Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 70 near the shore to around 60 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 82 to 89 near the shore to around 75 above 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Partly cloudy with isolated showers. Lows 68 to 73 near the shore to around 61 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy. Showers likely in the evening, then scattered showers after midnight. Lows around 71. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 87. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows around 71. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with showers likely. Lows 62 to 68 in the valleys to around 58 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Breezy. Showers in the morning, then scattered showers in the afternoon. Highs 73 to 81 in the valleys to around 64 above 4000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Wednesday Night: Mostly cloudy. Breezy. Showers likely in the evening, then showers after midnight. Lows 63 to 69 in the valleys to around 58 above 4000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

North Kaua’i

Tonight: Mostly cloudy. Showers in the evening, then showers likely after midnight. Lows 64 to 71. East winds 10 to 15 mph. Chance of rain 80 percent.

Wednesday: Partly sunny with scattered showers. Highs 75 to 85. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 64 to 72. East winds 10 to 15 mph. Chance of rain 70 percent.

East Kaua’i

Tonight: Mostly cloudy with showers likely. Lows 63 to 74. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy. Showers likely in the morning, then scattered showers in the afternoon. Highs 73 to 84. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday Night: Mostly cloudy. Showers likely in the evening, then showers after midnight. Lows 64 to 74. East winds around 10 mph. Chance of rain 90 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trades will deliver clouds and showers to windward and mauka areas through the week, with some decaying showers reaching leeward areas as well. A few downpours and even a rumble or two of thunder will be possible Thursday and Friday as a disturbance aloft moves over the island chain. A steady decrease in shower coverage and intensity with progressively nicer weather is expected the latter half of Memorial Day weekend.

Discussion

Current radar and satellite trends show partly cloudy skies, with a few showers riding on the trades. With moderate to locally breezy trades through Wednesday, expect windward and mauka showers with isolated spillover to leeward areas.
Wednesday the weak upper level low that has lingered just to the northeast of the Big Island moves at a glacial pace off to the east- northeast. This slow movement should slightly strengthen trades through Thursday. In the meantime another cut off low pressure system to the northwest of Kauai is moving in, deepening and will be the focus for weather Wednesday evening through the weekend.
As this low moves closer to the western end of the state and deepens temperatures aloft go from around -9C to -12 to -14C, lapse rates around 7.0 C/km and and CAPE values ranging from 900-1500 J/kg a few thunderstorms are possible along with some heavy downpours late Wednesday evening through Saturday. This low weakens and moves off to the northwest Sunday resulting in a reduction of showers and a progressively drier holiday weekend.

Aviation

A locally breezy trade wind flow will persist through the next several days. Some low-level turbulence is expected over and downwind of terrain, but since the inversion is slightly weak and elevated, conditions do not support AIRMET Tango at this time. Pockets of moisture within the trades will produce areas of MVFR conditions along windward slopes, where AIRMET Sierra for mountain obscuration will be possible during the overnight hours. Aside from afternoon clouds and spotty showers over the Kona slopes of the Big Island, VFR will dominate over leeward areas. An upper-level low moving overhead will bring higher chances for heavier showers and a thunderstorm by Thursday.

Marine

Surface high pressure building in far north of the islands will maintain moderate to locally strong trades through Friday. A Small Craft Advisory (SCA) is in effect for the typically windy waters around the Big Island and Maui through Thursday morning, but will likely need to be extended through at least Friday. The high is forecast to retreat westward during the weekend as a series of fronts pass to the far north, favoring a slight decrease in winds across the islands.
Surf along south facing shores will remain just below seasonal average through Thursday. A small, long period, south southwest swell will filter into the area late Thursday and bring surf near the summer average along south facing shores through this weekend. Surf will then slowly decline Sunday through early next week.
East shore surf will remain near seasonal average during the next couple of days. A gradual decline in east shore surf is expected during the weekend and early next week. Tiny surf will prevail along north facing shores this week and into the weekend.

HFO Watches/Warnings/Advisories

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

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