West Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 75 near the shore to around 66 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Friday: Sunny and breezy. Isolated showers in the morning. Highs 86 to 93 near the shore to around 78 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Friday Night: Mostly clear. Breezy. Isolated showers after midnight. Lows around 74 near the shore to around 65 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 73 to 78. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs 80 to 90. Northeast winds 15 to 25 mph. Chance of rain 20 percent.

Friday Night: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 75. Northeast winds 15 to 25 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 71 in the valleys to around 64 above 4000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 75 to 83 in the valleys to around 68 above 4000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Friday Night: Windy. Mostly cloudy with scattered showers. Lows around 70 in the valleys to around 62 above 4000 feet. East winds up to 30 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 67 to 77. Southeast winds up to 15 mph. Chance of rain 40 percent.

Friday: Breezy. Mostly sunny with scattered showers. Highs 73 to 89. East winds up to 20 mph. Chance of rain 40 percent.

Friday Night: Breezy. Partly cloudy with scattered showers. Lows 66 to 76. East winds 10 to 20 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 70 to 78. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 78 to 86. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers. Lows 69 to 77. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A strong high will build north of the state while remnants of Fausto continues to weaken and shifts far northwest. Breezy easterly trades will strengthen to locally windy levels Friday afternoon and evening then hold into Saturday. Low inversion heights could further accelerate winds in complex terrain that may warrant a Wind Advisory Friday afternoon into Saturday. Trades will ease back to the usual moderate to locally breezy levels Sunday into early next week as the high weakens. Typical summertime showers are expected for windward and mountain areas.

Discussion

A surface high far north of the state is driving breezy easterly trade winds across the state. Satellite and radar show scattered clouds with limited light showers mainly along windward and mauka areas, with minimal rainfall statewide this afternoon. The high will strengthen tonight through Friday as remnant low Fausto weakens far northwest of the state. Expect an increase in clouds and showers mainly along windward and mauka tonight as a low level deck of clouds and showers moves from east to west.
Breezy to locally windy trades are expected Friday afternoon into Saturday under a dry and stable airmass that will lower inversion heights to around 5,000 ft. Under these conditions winds could be accelerated downslope, near mountain tops and ridges, through gaps in the terrain, and in areas typically exposed to the trade winds that may warrant a wind advisory. However, uncertainty remains between the high resolution model guidance running a little stronger and earlier than the global models. With the drier airmass, dewpoints are expected to dip below 70 degrees, offering relief from the recently hot and muggy conditions.
Trades will weaken to moderate to locally breezy levels Sunday into early next week as Hurricane Genevieve tracks far northeast of the state, disrupting the trade wind flow. Another round of hot, muggy conditions could develop by the mid-week as remnant moisture from Genevieve moves over the state.

Aviation

Moderate to breezy trade wind weather will prevail through the forecast period. Some MVFR ceilings and visibility in SHRA may accompany showers mainly over the windward and mauka areas.
No AIRMETs are currently in effect. AIRMET TANGO may be possible over and immediate S through W of the eastern islands on Friday.

Marine

The remains of Fausto are about 300 miles northwest of Kauai this afternoon. As it continues to move away from the islands, trade winds will become better established from east to west across the island chain, due to the high pressure system far northeast of the islands. Trades are expected to increase Friday, with several global and high resolution models showing Small Craft Advisory (SCA) level winds reaching more of the coastal waters. As such, the SCA for the typical windier waters near Maui County and the Big Island remains in effect through tonight, and then expands to all coastal waters east of Oahu Friday morning. The SCA may need to be expanded to additional waters over the weekend. A weakness in the ridge to the north of the islands could cause trade winds to weaken again for early next week.
No advisory level surf is expected through the next week. The medium period south swell is peaking this afternoon, and is expected to gradually fade through the weekend. A mix of small south swells over the next few days will maintain surf along south facing shores slightly below the seasonal average.
An easterly swell is expected to arrive tonight and persist through the weekend. This swell is a combination of the short period trade wind swell, and the medium to long period east swell generated by Hurricane Genevieve in the East Pacific. North shores will see flat to tiny surf through early next week, with no significant north swells expected.

Fire weather

Breezy trades will continue to strengthen to locally windy levels across the state by Friday afternoon and evening. A drier and more stable airmass will drop inversion heights to around 5,000 ft Friday afternoon into Saturday that could further accelerate winds downslope, along mountain tops and ridges and through gaps in the terrain. With the low inversion heights, chances of precipitation will be low and limited to windward areas. While KBDI will remain below the critical thresholds this hot, dry and windy pattern could make for some near critical fire weather concerns, especially for areas above the inversion height and in the windier areas. Trades are expected to return to more normal moderate to locally breezy levels Sunday into early next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory from 4 AM Friday to 6 AM HST Saturday for Big Island Windward Waters, Kaiwi Channel, Maui County Leeward Waters, Maui County Windward Waters.
Small Craft Advisory until 6 AM 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