West Kaua’i

Tonight: Mostly clear. Isolated showers after midnight. Lows around 74 near the shore to around 64 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Sunny. Highs 86 to 92 near the shore to around 78 above 3000 feet. Northeast winds 10 to 15 mph.

Friday Night: Mostly clear. Isolated showers after midnight. Lows around 75 near the shore to around 64 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Breezy. Partly cloudy with isolated showers. Lows 71 to 77. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Friday: Sunny and breezy. Highs 80 to 91. Northeast winds 10 to 20 mph.

Friday Night: Mostly clear. Breezy. Isolated showers after midnight. Lows 71 to 77. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Partly cloudy with isolated showers. Lows around 69 in the valleys to around 62 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Friday: Sunny. Highs 76 to 83 in the valleys to around 74 above 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon.

Friday Night: Partly cloudy with isolated showers. Lows around 69 in the valleys to around 62 above 4000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

North Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 66 to 76. East winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Sunny. Highs 73 to 88. East winds 10 to 15 mph.

Friday Night: Partly cloudy with isolated showers. Lows 66 to 75. East winds 10 to 15 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 67 to 77. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Sunny. Highs 80 to 87. Northeast winds 10 to 15 mph.

Friday Night: Partly cloudy with isolated showers. Lows 67 to 77. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trades will continue through early next week. These trades are relatively dry and stable, leading to typical summertime windward and/or upslope mauka light showers. Tropical Storm Lowell has formed well southeast of the state, and is currently forecast by NHC to eventually move W to WNW. It might approach the state between roughly Sep 4 and Sep 7, but at this time range, uncertainty is quite large. NHC will continue to issue forecasts every 6 hours as Lowell develops.

Discussion

Satellite shows mostly sunny skies for most of the state this afternoon, with exceptions confined to some windward and mauka areas. Showers have been isolated and light so far, with reports of just a few hundredths in most areas, up to a third of an inch in parts of windward Big Island. Winds were averaging 10 to 20 mph, with gusts 30 to 35 mph in the usual orographically-favored locations (such as Kahului, the Moloka'i airport, and near the top of the Ko'olaus, to name a few).
A large surface high pressure system was centered near 46N 158W this afternoon. It is forecast to remain nearly stationary through Saturday before retrograding westward through Monday. By Wednesday, it should move east and end up right about where it started. This will keep trade winds going well into next week. The lower levels of the atmosphere will stay relatively stable and dry through at least Tuesday. Therefore, expect typical summertime showers, mainly windward and mauka. Wind speeds are expected to stay elevated, but below wind advisory criteria. An increase in moisture may arrive Wednesday.
The National Hurricane Center has begun issuing forecasts for Tropical Storm Lowell. Long-range models show Lowell may move toward the state. General model consensus this far out shows that if it comes toward Hawaii, it could arrive sometime between the 4th and 7th. We will of course be monitoring this closely, and NHC will issue forecasts every 6 hours. The other storm named earlier today, Tropical Storm Karina, is not expected to pose a direct threat to the islands at this time. But this far out, nothing is certain.

Aviation

Moderate trades expected through the period. Low cigs and SHRA over windward and mauka slopes, focused across eastern Islands today, likely expanding to all Islands into Friday. MVFR conds in heavier SHRA, otherwise VFR prevails.
AIRMET Tango is in effect for mod low-level turb lee of terrain and may be needed for a few days.

Marine

Dominant high pressure will keep moderate to locally strong trade winds in place through the middle of next week. A Small Craft Advisory for the typically windier waters around Maui County and the Big Island will continue through tomorrow and will likely need to be extended for the next several days.
Surf along south facing shores will hold just below advisory levels through tomorrow as a small, long period south southwest swell continues. The swell will gradually fade through the weekend. Then another similar sized south swell is expected by the middle to the later half of next week.
Surf along east facing shores will remain rough and choppy due to persistent trade wind swell. A small, medium period east swell from Tropical Storm Iselle may fill in Friday, peak Saturday before slowly fading into early next week. Additional medium period east swell is possible next week, resulting from Tropical Storms Karina and Lowell. This swell will depend on their track and intensity.
Surf along north facing shores will remain tiny to flat.

Fire weather

Relatively dry air and moderate to locally breezy trade winds will continue to bring moderate fire weather concerns through early next week. Conditions may get close to criteria if the approaching airmass proves to be drier than forecast, especially Friday and Monday.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov