West Kaua’i

Tonight: Mostly clear. Breezy. Isolated showers after midnight. Lows around 68 near the shore to around 58 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Friday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 84 near the shore to around 73 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday Night: Partly cloudy with isolated showers. Lows around 69 near the shore to around 59 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 70. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Mostly cloudy with numerous showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs 76 to 85. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers. Lows around 70. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 61 to 67 in the valleys to around 56 above 4000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Friday: Breezy. Occasional showers in the morning, then scattered showers in the afternoon. Highs 72 to 78 in the valleys to around 63 above 4000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 61 to 67 in the valleys to around 57 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy with scattered showers in the evening, then mostly cloudy with numerous showers after midnight. Lows 62 to 71. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 70 percent.

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

Friday Night: Mostly cloudy with scattered showers. Lows 62 to 71. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 73. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Friday: Occasional showers in the morning, then scattered showers in the afternoon. Highs 71 to 82. East winds 10 to 15 mph. Chance of rain near 100 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 63 to 72. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to breezy trades will continue for the next several days. Showers are expected across windward and mauka areas with limited spillover into leeward areas. A nearly stationary upper- level low northeast of the islands will enhance clouds and showers through Friday. By the weekend, the upper low is forecast to move northeast away from the state and wind speeds will decrease slightly. From Monday through the end of next week, trade wind showers, mainly windward and mauka, will continue.

Discussion

Moderate to breezy trade winds are forecast to continue thanks to a series of high pressure systems that will move from west to east across the north Pacific over the coming week. An upper-level low centered 600-700 miles northeast of the state is causing some local instability resulting in deeper clouds and some enhanced shower activity across windward and mauka areas, with isolated showers reaching leeward areas. This upper-level low will remain nearly stationary through Friday, keeping some cold air aloft over the region. This will continue the risk of occasional moderate to briefly heavy showers.
The trade pattern will be with us for the next week. Wind speeds should weaken slightly Saturday into Sunday as the upper-level low exits the region to the northeast. Periods of showers will continue to favor windward and mauka areas. From Monday through most of next week, expect trades to continue with only slight variations in day-to-day wind speeds. Showers will fall mainly windward and mauka, as usual in a trade wind pattern.

Aviation

A stationary upper low is situated northeast of Hawaii that will enhance some of the incoming low clouds and showers that will focus windward by fresh trade winds. Will be monitoring for mountain obscurations due to showers over windward slopes tonight, but coverage is brief/isolated for now.
AIRMET Tango is posted for tempo moderate turbulence across leeward sides of all islands below 8000 feet due to the breezy trade winds. Expect this AIRMET to continue into Friday.

Marine

A 1031 mb high far north of the state will strengthen slightly during the next 24 hours and will bring a brief increase of our trade winds with widespread fresh to strong trade winds expected across the state. ASCAT pass from earlier today showed some strong winds already over the Kauai Channel. With the winds expected to strengthen tonight, the Small Craft Advisory has been expanded in area and now includes all Hawaiian Waters through Friday. Winds should decrease late Friday into the weekend, as a front passing far north of the state will nudge the aforementioned high further east and allow trade winds to decrease to moderate to locally fresh speeds. Some of the windier areas around Maui County and the Big Island could still see locally strong winds over the weekend.
The current small, northwest to north-northwest (320-335 degree), swell will slowly decline into Friday and produce near average surf along north facing beaches. A compact storm-force low developed just east of the Kuril Island on Monday and tracked toward the Aleutian Islands for a few days. This storm should send a moderate, long-period northwest (320 degree) swell towards the islands late Friday into Saturday and generate above average surf along north and west facing shores on Saturday. Average H1/10 heights for north facing shores is 6 feet for the month of May (Goddard-Caldwell Database). However, surf heights should remain below advisory levels.
Surf along south-facing shores will remain small through the rest of this work week, with mainly background south to southwest swell expected. A small, long period, south-southwest pulse should arrive late Friday and give a bump up to south facing shores through this weekend.
Surf along east-facing shores will see a boost tonight into Friday as the trades briefly strengthen to widespread fresh to strong trade winds. Trades will then slowly weaken this weekend and allow surf along east-facing shores to decrease to below average levels by early next week.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov