West Kaua’i

Tonight: Mostly clear. Isolated showers after midnight. Lows around 73 near the shore to around 63 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Saturday: Sunny. Isolated showers in the morning. Highs 84 to 91 near the shore to around 76 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Saturday Night: Mostly clear. Isolated showers after midnight. Lows around 73 near the shore to around 62 above 3000 feet. East winds 10 to 15 mph shifting to the northeast after midnight. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 71 to 77. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 79 to 89. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 71 to 76. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 65 to 70 in the valleys to around 60 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Saturday: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 74 to 81 in the valleys to around 66 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Saturday Night: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows around 67 in the valleys to around 60 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Partly cloudy with scattered showers. Lows 64 to 74. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

Saturday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 71 to 85. East winds up to 15 mph. Chance of rain 50 percent.

Saturday Night: Partly cloudy with scattered showers. Lows 64 to 74. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 67 to 77. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Mostly cloudy with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 85. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 67 to 77. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Breezy trades are expected to slightly decrease on Sunday and remain at moderate to locally breezy speeds through early next week. Light passing showers will focus mostly over windward and mountain areas during the night time and early morning hours. Occasional leeward showers will be possible. Wetter trade wind conditions are expected next week as areas of enhanced moisture are forecast to move through the islands starting as early as Sunday night.

Discussion

Fairly typical summer time trade wind weather is expected through the weekend with light passing showers riding in with our moderate to breezy trade winds. As the high far north of the state drifts further northeast, we should see a slight decrease of our trade winds on Sunday. Soundings from Hilo and Lihue also show our typical trade wind weather with the 00Z sounding showing the trade wind inversion at roughly 6500 feet and precipitable water values of around 1.2 inches.
By next week, models indicate a few batches of enhanced moisture and higher dewpoint temperatures arriving, boosting shower chances. GFS model cross section data on Monday currently shows a plume of moisture with a depth up to 10,000 ft passing through the islands. While the upper level dynamics remain very weak, the enhanced moisture combined with orographic lifting should allow for some brief periods of moderate showers over windward and mountain areas Sunday night into Monday.
Then Tuesday into Wednesday, a plume of deeper moisture arrives with dewpoints up into the low 70s. This would translate to more widespread trade wind showers and more frequent leeward spillover showers. Areas that do not see frequent showers will be hot and muggy due to the warm dewpoint temperatures. While the upper level dynamics does not look great either on the second plume of moisture, there is an upper level low far west of the state that could enhance precipitation if the upper low gets close enough to the state. Nonetheless, with the abundant moisture expected by the middle of next week, some brief heavy showers will be possible. Stay tuned for updates.

Aviation

Moderate to breezy trades will continue through Saturday. Low clouds and scattered showers will favor windward and mauka areas as areas of moisture move in. Expect MVFR windward and mauka due to low clouds, and brief MVFR conditions in showers. VFR expected elsewhere.
AIRMET Sierra is in effect for mountain obscurations for windward sections of Kauai, Oahu, Molokai, Maui, and the Big Island. Conditions may continue overnight due to the ongoing and upstream showers.
AIRMET Tango is in effect for moderate turbulence downwind of terrain due to the breezy trade winds and will continue through the forecast period.

Marine

High pressure far north of the state will gradually shift further northeast through the weekend then remain nearly stationary through early next week. This will allow moderate to locally strong trades to persist through Saturday, then slightly decrease Sunday into early next week. A Small Craft Advisory (SCA) remains in effect for the typically windier waters around Maui and the Big Island through Saturday afternoon. Winds will be borderline SCA levels Sunday into early next week.
A small, medium-period south swell will gradually ease into Saturday. Surf will fall below seasonal averages by tonight. Another small, long-period south swell will arrive and fill in on late Saturday, then peak on Sunday before gradually declining early next week. This swell should boost surf heights back up to near normal for this time of year.
Surf along east facing shores will remain rough and choppy with a slight decline possible early next week due to minor fluctuations of our trades. Surf heights along north facing shores will remain tiny through the first half of next week. A tiny bump in surf is possible for north-facing shores on Saturday with the arrival of a very small, medum-period west-northwest swell.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov