West Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 70 to 75 near the shore to around 63 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Friday: Mostly sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Highs 86 to 92 near the shore to around 78 above 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Friday Night: Partly cloudy with isolated showers. Lows 69 to 76 near the shore to around 62 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Partly cloudy with scattered showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 81 to 90. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Partly cloudy with scattered showers in the evening, then mostly cloudy with numerous showers after midnight. Locally heavy rainfall possible after midnight. Lows around 68 in the valleys to around 60 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Friday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 75 to 85 in the valleys to around 68 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Friday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Locally heavy rainfall possible after midnight. Lows around 68 in the valleys to around 60 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Locally heavy rainfall possible after midnight. Lows 66 to 75. East winds 10 to 15 mph. Chance of rain 70 percent.

Friday: Partly sunny with scattered showers. Highs 78 to 87. East winds up to 15 mph. Chance of rain 50 percent.

Friday 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: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Locally heavy rainfall possible after midnight. Lows 65 to 77. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Friday: Partly sunny with scattered showers. Highs 74 to 87. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Locally heavy rainfall possible after midnight. Lows 65 to 76. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Seasonal high pressure to the north will maintain moderate to breezy northeast to easterly trade winds through next week. An area of enhanced moisture along with weak mid level troughing will increase trade wind showers tomorrow and Saturday. Showers should then decrease back to typical summertime amounts next week as drier air moves back in on the trade wind flow.

Discussion

A stable pattern is firmly established as a 1034 mb high pressure far north of the region remains in place. A minor decrease in stability tomorrow into this weekend is possible as a weak mid to upper level low edges in just north of the area and a mid level trough moves in from the east. This weak upper low and mid level trough could provide a small boost in lift for the islands Friday and Saturday before weakening Sunday and a more stable pattern returns for next week.
Observational data today from radar and satellite show a typical trade wind cloud and shower distribution and the balloon launch from this afternoon shows inversion heights around 6,000 ft. The inversion heights are expected to be raised across the region through the weekend as the instability from the mid level trough and upper low creeps in. Current model guidance shows trade wind showers increasing early tomorrow morning for Kauai and Oahu as low and mid level moisture moves through the area under the weak upper level low and trough. Any showers that do develop statewide will likely be a bit more heavy. This feature along with its associated moisture should weaken Sunday and a more dry and stable trade wind pattern will return Monday through next week.

Aviation

Locally breezy trade winds will prevail across the islands with occasional passing showers favoring the typical windward and mountain locations. A slight uptick in shower activity is possible during the overnight hours across windward areas, primarily across the western islands. Otherwise, VFR conditions are expected Friday.
Due to the locally breezy trades, AIRMET Tango for low level turbulence below 7,000 feet will continue through early Friday. Winds are expected to ease by Friday night.

Marine

High pressure will remain far northeast of the state through the rest of the week. Fresh to locally strong trades will persist through Friday, then drop slightly as a weak low-level trough moves through the state from the east through the weekend. The Small Craft Advisory (SCA) has been extended through Friday afternoon for the typical windy areas around Maui County and the Big Island.
Fading south and south-southeast swells will maintain below average surf on south facing shores through Friday. A slight bump in surf is expected this weekend as a new long-period southwest swell arrives from the Tasman Sea, along with a small short-period south-southeast swell. The Tasman swell is expected to peak Saturday, with surf heights topping near the summer average, before gradually declining into early next week.
Surf along east facing shores will continue to remain rough and choppy due to the fresh to locally strong trade winds. Surf along north facing shores will remain nearly flat through the weekend.
Minor coastal flooding along the shoreline and in low-lying coastal areas will be possible around the daily high tide starting Monday of next week due to peak monthly tides and higher than predicted water levels at select locations.

Fire weather

Fire weather concerns will lower tomorrow into this weekend as a wetter pattern develops across the state. Trade winds will remain light to locally breezy through the day before slightly weakening this weekend. A higher frequency of showers is expected tomorrow morning through Sunday morning. Drier, more stable weather is expected to return Sunday afternoon through next week. This may increase the fire weather threat over more leeward areas that do not receive the benefit of weekend rain.

HFO Watches/Warnings/Advisories

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