Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly sunny with isolated showers. Highs 77 to 86 near the shore to around 72 above 3000 feet. Northeast winds up to 10 mph shifting to the west in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Lows 64 to 69 near the shore to around 57 above 3000 feet. Light winds.

Thursday: Mostly sunny. Scattered showers in the afternoon. Highs 76 to 84 near the shore to around 69 above 3000 feet. Light winds. Chance of rain 40 percent.

South Kaua’i

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 85. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows around 67. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny. Isolated showers in the afternoon. Highs 76 to 84. Light winds. Chance of rain 20 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 72 to 78 in the valleys to around 63 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 57 to 66 in the valleys to around 55 above 4000 feet. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 71 to 77 in the valleys to around 63 above 4000 feet. Light winds becoming north up to 10 mph in the afternoon. Chance of rain 40 percent.

North Kaua’i

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 73 to 81. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 60 to 67. East winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Thursday: Mostly sunny. Scattered showers in the afternoon. Highs 73 to 80. Light winds. Chance of rain 40 percent.

East Kaua’i

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 71 to 82. Northeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 60 to 70. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 71 to 82. Light winds. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trades will ease today and tonight. Trade showers are expected to diminish as well, though some showers could linger for windward Big Island and Maui through tonight. A relatively weak and disorganized cold front will push down the chain Thursday night through Saturday. Unstable air associated with the front should enhance showers during this period, with a small chance for a couple rumbles of thunder for Maui and the Big Island on Friday. More stable and dry air should fill in behind the front on a rather cool northerly flow which will shift around to northeast trades over the Holiday weekend.

Discussion

Currently at the surface, a 1029 mb high is centered around 1200 miles north-northeast of Honolulu, while a cold front is positioned around 900 miles west-northwest of Kauai. The resulting gradient is producing moderate to locally breezy trade winds across the island chain early this morning. Infrared satellite imagery shows partly to mostly cloudy conditions in windward areas as well as leeward sections of the Big Island, with clear to partly cloudy skies elsewhere. Main short term focus revolves around trade wind trends and rain chances.
Moderate to locally breezy trades will ease up today through Thursday as a front approaches from the northwest. The winds will become light enough to allow land and sea breezes to dominate late tonight and Thursday. A cold front will then slide southeastward down the island chain Thursday night through early Saturday. Light to moderate west to southwest winds will develop in advance of the front, while moderate northwest to north winds fill in behind it. The front should have cleared the Big Island by late Saturday, with moderate to locally breezy northeasterly trades expected Saturday night through Sunday night as high pressure builds eastward to the north of the state. The trades will then ease up again early next week as the next front approaches the island chain from the northwest.
As for the remaining weather details, fairly typical trade wind weather will prevail this morning with showers favoring windward slopes and coasts. Mid-level ridging will build over the islands reducing shower coverage considerably this afternoon and tonight. The exception may be over windward Maui and the Big Island where an area of enhanced moisture appears to move in from the east bringing an increase in shower activity tonight. Fairly dry and stable weather will continue on Thursday, with morning showers favoring windward sections of Maui and the Big Island, with a few daytime heating showers developing over the interior of the islands in the afternoon. There remains some uncertainty regarding the timing and strength of the late week cold front, but overall we should see an increase in showers in association with the front as it progresses southeastward down the island chain Thursday night through Saturday. There is a slight chance for thunderstorms over the higher terrain of Maui and the Big Island Friday afternoon, which could bring some wintry precip to the summits of Mauna Loa and Mauna Kea if they occur. Behind the front drier and more stable conditions will build in. Fairly dry and stable conditions should then prevail Saturday night through early next week, with showers limited primarily to windward slopes and coasts.

Aviation

Moderate trades slightly weakening through tonight as a cold front approaches from the northwest. Low cigs and SHRA should be focused over windward and mauka areas. Brief MVFR conds can be expected in SHRA but otherwise, VFR should prevail.
No AIRMETs are in effect.

Marine

A cold front and low pressure system passing just north of the island chain will weaken the trade winds through the day. A light wind regime with expanding near shore land and sea breezes will expand in coverage from Thursday through the end of the week. The cold front will move into the northwestern Hawaiian Islands Thursday night then slide southeastward down the island chain into Saturday supported by an upper level trough. Expect numerous showers with this next system, including the potential for thunderstorms over the easternmost waters.
The current long period northwest swell will continue to decline today. The forerunners of the next significant northwest swell will move into the islands by Thursday night, and then swiftly build above warning thresholds along exposed north and west facing shores from late Friday into Saturday, then falling to advisory thresholds by Sunday. Another medium period northwest swell is forecast to fill in from Tuesday to Wednesday of next week, keeping surf heights elevated along north and west facing shores.
Surf along south facing shores will remain very small through this afternoon. A small long period south swell boost will develop from tonight into Thursday, peaking by Friday, and slowly lowering through the weekend. PacIOOS buoy observations located in American Samoa peaked above model guidance, suggesting surf may peak near or just below High Surf Advisory levels.
Surf along east facing shores will slowly decline through the end of the week as trade winds diminish. A small north swell could potentially elevate surf along exposed shorelines on Wednesday and Thursday.

Fire weather

No critical fire conditions anticipated during the forecast period, although we will keep an eye on Saturday and Sunday which could feature the lowest post-frontal relative humidities and a relative peak in N or NE winds. For now, both wind speeds and humidity levels are not expected to reach Red Flag Warning criteria concurrently, but guidance suggests it may be close, particularly on Sunday.

HFO Watches/Warnings/Advisories

None.

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