West Kaua’i

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 72 near the shore to around 63 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Highs 84 to 91 near the shore to around 76 above 3000 feet. East winds up to 10 mph.

Thursday Night: Partly cloudy. Lows around 72 near the shore to around 63 above 3000 feet. Northeast winds up to 10 mph.

South Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 71 to 76. Northeast winds around 15 mph. Chance of rain 40 percent.

Thursday: Mostly sunny. Isolated showers in the morning. Highs 78 to 89. Northeast winds around 15 mph. Chance of rain 20 percent.

Thursday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with scattered showers. Lows around 68 in the valleys to around 61 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 74 to 81 in the valleys to around 67 above 4000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows around 67 in the valleys to around 60 above 4000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

North Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 64 to 74. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Mostly sunny with isolated showers. Highs 71 to 85. East winds 10 to 15 mph. Chance of rain 20 percent.

Thursday Night: Partly cloudy with isolated showers. Lows 64 to 74. East winds 10 to 15 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 68 to 75. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Mostly sunny with isolated showers. Highs 77 to 85. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Thursday Night: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 67 to 75. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

A ridge to the north of the islands will weaken slightly through the latter half of the week, allowing trade winds to diminish briefly to moderate levels Thursday night into Friday before gradually restrengthening back to locally breezy over the weekend. Clouds and showers will remain focused mainly along windward and mauka areas into early next week. A drier airmass moving in from the east is expected to limit shower activity into the weekend.

Discussion

High pressure remains far north-northeast of the islands today with an associated ridge near 40N. This will produce moderate easterly trade winds which should be locally breezy through Thursday before a slight weakening of the ridge induces a slight reduction in trades Thursday night into Friday. Then, the high is expected to sink southward slowly this weekend, which will allow trade winds to gradually restrengthen.
A drier airmass moving into the islands, as indicated in satellite derived precipitable water, will linger into the weekend. Expect a return to drier conditions, with dew points already beginning to drop below 70 degrees at some locations this afternoon, and less coverage of rain showers. Otherwise, the typical trade wind showers will focus along the windward and mauka areas, which will be most widespread at night and in the early morning hours.
Looking into next week, the remnant low of Tropical Storm Douglas in the Eastern Pacific is forecast to track to the northeast of the islands. At this point, impacts appear limited, with an increase of rain showers possible some time mid to late next week with trailing moisture.

Aviation

Moderate to locally breezy trades will continue through the holiday weekend. Showers will be limited over the next couple of days, but are still possible primarily over windward and mountain areas. Expect MVFR conditions in showers, and VFR elsewhere.
AIRMET Sierra is in effect for mountain obscurations for windward areas of Maui due to ongoing and upstream showers. Other windward areas may have mountain obscurations later tonight due to overnight showers, with windward Big Island being the most likely.
AIRMET Tango is currently in effect for moderate turbulence downwind of terrain due to breezy trade winds.

Marine

Surface high pressure far north of the islands will maintain moderate to locally strong trade winds through Thursday before declining slightly to become moderate to fresh through the rest of the forecast period. The Small Craft Advisory (SCA) is in effect through Thursday afternoon for the windier waters and channels around Maui County and the Big Island.
A small, medium-period south swell will linger through Thursday just below the summertime average. This fading swell combined with a series of small, medium- to long-period south- southwesterly swells, will deliver below-average surf along south-facing shores through Friday. Over the holiday weekend and into early next week, a moderate, long-period south-southwest swell will arrive, boosting surf heights to near High Surf Advisory levels potentially Sunday into Monday.
Surf along east facing shores will remain rough and choppy through Thursday as trade winds remain locally strong. Surf along north facing shores will remain flat to tiny through the forecast period, with a minor uptick possible Friday into the holiday weekend as a small, medium-period northwest swell arrives.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov