West Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 71 near the shore to around 61 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs 81 to 87 near the shore to around 74 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy with isolated showers. Lows around 71 near the shore to around 61 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 71. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Sunday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 86. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Sunday Night: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 72. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 64 to 69 in the valleys to around 59 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Sunday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 80 in the valleys to around 65 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 64 to 70 in the valleys to around 59 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 72. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 75 to 82. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows 66 to 73. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 73. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Sunday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 83. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows 65 to 73. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Upper ridging will become established over the coming week. There is a weak surface trough that will move west and exit the state through Monday. This will bring increased showers to western islands through Sunday. An upper level low may develop mid-week to our northeast, but it is unclear what, if any, impact it will have on our weather. The main story for the next week is trade winds, increasing in speed tonight into Sunday, bringing mainly windward and mauka showers.

Discussion

Showers were numerous this afternoon across the Kona region on Big Island and across Oahu, and isolated to scattered on other islands. Between low clouds associated with the showers, and high clouds streaming northeast, skies were mostly cloudy early this afternoon. Trade winds were building in across the region, with northeast winds averaging 10 to 20 mph with gusts 20 to 30 mph in most areas.
Over the next few days, a weak broad trough aloft to our north will be replaced with a ridge. This change aloft will help create a stronger surface ridge to the north, and this will strengthen our developing trade winds. A weak surface trough, associated with an increase in moisture, was moving west through the central islands this afternoon. It is expected to continue slowly moving west as it weakens further, exiting the state by Monday. As it does, expect areas of showers to continue to develop and be carried west or WSW on the developing trade winds.
These trades will strengthen through Sunday, and remain moderate to breezy through most of the coming week. Upper ridging to our north will be the dominant feature of the coming week. However, models are coming into better agreement that an upper low may interrupt the ridge beginning around the middle of next week. There is little agreement on how strong this low might be or exactly where it will be positioned. The general consensus at this time is for it to form sometime between Wednesday and Friday, most likely to our northeast. It could end up being a factor in our weather (increased chance of rain and/or weakening trades), but it is too early to be sure. Otherwise, expect a typical trade wind pattern beginning Monday, with showers mainly windward and mauka.

Aviation

Moderate trades this afternoon will weaken some tonight, then steadily increase throughout the day Sunday becoming locally breezy by the afternoon. A weak trough currently passing through the state will increase showers, especially over windward and mountain areas with periods of MVFR conditions expected throughout the rest of the afternoon. A drier airmass will move in from the east this evening, which should bring a decrease of showers tonight from east to west. One exception is over Kauai, where showery conditions are expected to persist through tonight. Sunday should be a much drier day with some lingering moisture near Kauai.
AIRMET Sierra remains in effect for mountain obscuration over Kauai, Oahu, Molokai and Maui due to the passing showers. AIRMET Sierra should get cancelled from east to west tonight as the drier air moves in.
AIRMET TANGO is also in effect for moderate upper level turbulence for Kauai and Oahu due to a strong jet over the state. Upper level turbulence will generally decrease on Sunday, but some light turbulence is still expected throughout the day.
Also, there will likely be a need for AIRMET Tango for low-level turbulence as trades gradually strengthen Sunday afternoon into the evening.

Marine

A ridge will remain in place north of the islands with fresh trade winds tonight, strengthening Sunday and Sunday night and maintaining next week. A Small Craft Advisory (SCA) is posted for waters around Kauai and windward Oahu, and waters around Maui County and Big Island through tonight.
A small northwest swell will maintain through the rest of the weekend, shifting out of the north to north northwest next week. Small south swell will fade this weekend with a small, long period reinforcement Monday through Thursday. Surf along east facing shores will remain below normal this weekend, but will gradually increase next week as trade winds strengthen.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Sunday for Kauai Channel, Kauai Leeward Waters, Kauai Northwest Waters, Kauai Windward Waters, Oahu Windward Waters.
Small Craft Advisory until 6 AM HST Monday for Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters, Maalaea Bay, Pailolo Channel.

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Data Courtesy of NOAA.gov