West Kaua’i

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 68 to 74 near the shore to around 61 above 3000 feet. Northeast winds around 10 mph. Chance of rain 50 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 85 to 91 near the shore to around 77 above 3000 feet. East winds around 10 mph. Chance of rain 50 percent.

Saturday Night: Partly cloudy with isolated showers. Lows 69 to 75 near the shore to around 62 above 3000 feet. East winds around 10 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 72. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Saturday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 80 to 88. East winds 10 to 15 mph. Chance of rain 70 percent.

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

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 64 to 69 in the valleys to around 59 above 4000 feet. East winds 10 to 20 mph decreasing to up to 20 mph after midnight. Chance of rain 70 percent.

Saturday: Breezy. Mostly cloudy with numerous showers. Highs 75 to 84 in the valleys to around 67 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Saturday Night: Breezy. Occasional showers in the evening, then numerous showers after midnight. Lows 65 to 70 in the valleys to around 59 above 4000 feet. East winds 10 to 20 mph. Chance of rain near 100 percent.

North Kaua’i

Tonight: Mostly cloudy with numerous showers. Lows 65 to 74. East winds 10 to 15 mph. Chance of rain 70 percent.

Saturday: Partly sunny with scattered showers. Highs 78 to 87. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 65 to 74. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy with numerous showers. Lows 64 to 76. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 86. East winds 10 to 15 mph. Chance of rain 70 percent.

Saturday Night: Mostly cloudy with numerous showers. Lows 64 to 76. East winds around 10 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

High pressure far northeast of the state will lead to moderate to locally breezy trade winds. Expect to see fairly typical summertime weather as clouds and showers favor windward and mauka areas, with an uptick in showers this weekend and early next week.

Discussion

A 1033 mb high remains nearly stationary far northeast of the state. Water vapor imagery shows a compact upper level low several hundred miles north of us that is slowly drifting westward. Even with the upper low nearby, 00z soundings show a typical subsidence inversion just under 7kft at Lihue and down to 5kft at Hilo. Rainfall amounts across the state have been roughly a quarter to a half inch over the past 12 hours, with more of those reports across Kauai and Oahu.
The high northeast of the state will gradually shift northward over the next couple days, but we'll remain in a pretty consistent trade wind flow. While the upper low is expected to stay north of the state, a shortwave trough rotating around it will help raise inversion heights this weekend. A pocket of moisture just outside the offshore waters, apparent as a showery band of cumulus on satellite imagery, will enhance rainfall chances this weekend. Trade winds speeds may lower a bit but still remain borderline breezy. While the trades will focus most rainfall across windward sections, there will be some brief showers reaching leeward areas as well.
12z/18z models show another pocket of moisture farther east (east of 140W) tracking across the state early next week. MIMIC Total Precipitable Water imagery shows higher values in this area (about 1.6-1.8 inches) compared with the first band at the edge of our offshore waters (about 1.3-1.5 inches). The GFS is more aggressive bringing this moisture across the state Monday/Tuesday, with the ECMWF fading out the signal more. Either way should lead to an uptick in windward showers early next week, with some rain reaching leeward as well. It's interesting to note that the NBM lights up showers across the Kona slopes on the Big Island Monday afternoon more than any day this forecast period.
Beyond Tuesday, we return to a more typical summertime trade wind pattern with showers focused primarily at night and during the early morning. Wind speeds may also ramp back up a notch during next week as the high northeast of us strengthens slightly.

Aviation

High pressure to the northeast will maintain moderate to locally breezy easterly trade winds into the early evening, with a slight downward trend tonight and tomorrow. Clouds and showers will favor windward and mountain areas across all islands, with the best coverage late tonight into tomorrow morning, as well as the Kona slopes of the Big Island during daytime hours. Brief MVFR conditions will be possible in showers. Otherwise, VFR conditions will generally prevail.
AIRMET Tango is in effect for moderate turbulence below 8000 feet to the lee of mountains for all Hawaiian islands, due to the locally breezy trades and the stable atmosphere.
AIRMET Sierra might be needed later tonight into tomorrow morning due to incoming tradewind showers.

Marine

High pressure far northeast of the waters will continue to drive moderate to locally strong trade winds through tonight. The Small Craft Advisory (SCA) for the typical windy waters around Maui County and Big Island has been extended through tonight. There may be a short- lived lull in trade speeds Saturday as the high fluctuates in strength and position, reducing wind speeds below SCA criteria for some or all zones in the SCA. The high will strengthen next week while drifting north resulting in trade wind speeds increasing state wide and SCA conditions returning or remaining in effect for typically windy waters through the rest of the forecast period.
Surf along south facing shores will remain small through the weekend as a small background south southwest swell moves through. A small, long period south swell is expected to gradually build at the start of next week, with surf peaking near average Tuesday before slowly tapering off through the second half of next week. Rough, choppy east-facing shore surf may drop a touch over the weekend as trade winds ease slightly locally and upstream but should pick right back up next week. A very small northwest swell may pass through early next week, providing tiny surf along north facing shores Monday and Tuesday before becoming nearly flat through the remain forecast period.

Fire weather

Moderate to locally breezy trades will decrease slightly over the weekend before becoming locally breezy again next week. Despite the trade wind showers picking up across windward sections this weekend and early next week, afternoon relative humidities across leeward sections remain near summertime normals. Fairly typical fire weather conditions are expected.

HFO Watches/Warnings/Advisories

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

Kauai Now Weather is brought to you by Blue Hawaiian Helicopters.