Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly cloudy. Isolated showers early in the morning, then numerous showers in the late morning and afternoon. Highs 78 to 85 near the shore to around 71 above 3000 feet. South winds up to 15 mph shifting to the southwest in the afternoon. Chance of rain 70 percent.

Tonight: Cloudy. Scattered showers in the evening, then frequent showers after midnight. Lows 65 to 71 near the shore to around 59 above 3000 feet. West winds up to 10 mph shifting to the north after midnight. Chance of rain 90 percent.

Wednesday: Cloudy. Frequent showers in the morning, then scattered showers in the afternoon. Highs 76 to 85 near the shore to around 70 above 3000 feet. North winds up to 10 mph shifting to the south in the afternoon. Chance of rain 90 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 77 to 85. West winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Cloudy with scattered showers. Lows around 69. West winds 10 to 15 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Wednesday: Mostly cloudy with scattered showers. Highs 76 to 84. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 73 to 82 in the valleys to around 64 above 4000 feet. Southwest winds up to 25 mph with gusts to 45 mph. Chance of rain 50 percent.

Tonight: Breezy. Scattered showers in the evening, then frequent showers after midnight. Lows 59 to 68 in the valleys to around 57 above 4000 feet. Southwest winds up to 20 mph shifting to the west up to 10 mph after midnight. Chance of rain near 100 percent.

Wednesday: Frequent showers. Highs 69 to 76 in the valleys to around 62 above 4000 feet. Light winds becoming north up to 10 mph in the afternoon. Chance of rain near 100 percent.

North Kaua’i

Today: Partly sunny. Breezy. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 75 to 84. South winds up to 20 mph shifting to the southwest in the afternoon. Chance of rain 50 percent.

Tonight: Cloudy. Scattered showers in the evening, then frequent showers after midnight. Lows 62 to 70. West winds up to 15 mph. Chance of rain 90 percent.

Wednesday: Cloudy. Frequent showers in the morning, then scattered showers in the afternoon. Highs 71 to 79. Northwest winds up to 10 mph. Chance of rain 90 percent.

East Kaua’i

Today: Partly sunny. Breezy. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 72 to 85. Southwest winds 10 to 25 mph decreasing to up to 25 mph in the afternoon. Chance of rain 50 percent.

Tonight: Cloudy and breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 62 to 72. West winds up to 20 mph in the evening becoming light. Chance of rain 70 percent.

Wednesday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 69 to 82. North winds up to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A cold front will approach the islands today, bringing moist southerly winds and increasing rainfall chances. The front will reach Kauai tonight, then stall and diminish around Oahu and Molokai Wednesday through Thursday. Lingering residual moisture combined with an upper disturbance over the region will keep rainfall chances around through the second half of the week. As trade winds gradually return, the focus of rainfall will shift to windward and mauka areas later in the week through the weekend.

Discussion

The short-term guidance remains in good agreement, showing lowering upper heights over the region as a shortwave trough digs southeastward into the area today through midweek. The associated cold front is forecast to reach Kauai by tonight before stalling near Oahu and Molokai Wednesday through Thursday. While most of the dynamics and deeper moisture are expected to remain north of the state, increasing lift and pooling low-level moisture along the boundary will enhance the potential for some much needed rainfall across the islands, particularly over the dry leeward areas.
Ahead of the front, spotty and brief showers will continue to develop and lift northward across the islands today. This has already been the case for portions of the state overnight, with totals ranging between a tenth and around a quarter of an inch. The primary line of showers along the front should reach Kauai this evening and Oahu on Wednesday. With southwest flow prevailing, rainfall will primarily favor west- and south-facing slopes, with brief heavier showers possible. Breezy southwest winds, with speeds up to 25 kt at 850 mb, may result in periods of strong downsloping winds for windward areas later today.
Winds will shift out of the northwest behind the front over the western end of the state tonight into Wednesday, with northeast to east trade winds returning statewide Thursday through the weekend as high pressure builds north of the area. Residual moisture lingering near the stalled front, combined with an upper low pinching off over the eastern half of the state, will sustain rainfall chances into the second half of the week. With the trades in place, rainfall will primarily focus over windward and mauka areas.
Additional instability from the cold pool aloft may lead to a few heavier showers or even isolated thunderstorms, particularly from Oahu to the Big Island later this week as the upper trough moves into the area and begins to close off. For the Big Island summits, this setup could support periods of wintry precipitation from late Thursday through early Saturday.

Aviation

A cold front approaching the Hawaiian Islands from the northwest will produce increasing southwesterly winds and bands of showers moving northward into the southern and western slopes of all islands today. The weakening frontal cloud band will slow down as it brings clouds and showers into Kauai by tonight, and into Oahu by Wednesday morning. MVFR conditions will occur within any developing prefrontal shower bands and along the cold frontal cloud band. Periods of IFR conditions are possible for Lanai Airport (PHNY) in shower bands over the next 12 to 24 hours.
AIRMET Sierra in effect for tempo Mountain Obscuration over south through west sections of Oahu, Molokai, Maui and the Big Island.
AIRMET Tango in effect for Moderate Turbulence below 080 over and immediately north through east of island mountains of Kauai and Oahu.

Marine

Overlapping L to XL long-period NW swells will maintain High Surf Warning-level surf along most N and W facing shores through Thursday. See the High Surf Warning (CFWHFO) and Surf Zone Forecast for Hawaii (SRFHFO) for details. Average overnight swell heights and periods at NDBC buoys 51001/51101 NW of Kauai have been around 14 feet 15 seconds, supporting fairly steady surf heights today. Swell at these buoys will trend up toward XL heights later this afternoon and tonight, with peak surf likely occurring on Wednesday. As some of this swell is being generated by an extensive fetch of W to NW winds passing just N of the islands, a wide range of wave periods is expected.
NW swell will gradually diminish from Thursday into Saturday, with surf falling below High Surf Advisory heights by Saturday. A moderate NW swell is possible Sunday. Locally strong SW winds will bring choppy wind waves to S and W facing shores (especially on Kauai and Oahu) through tonight before diminishing.
Combined seas 10 feet or greater have prompted a Small Craft Advisory for all Hawaiian coastal waters (except Maalaea Bay) through Thursday. Additionally, SW winds will become strong over Kauai and Oahu waters today as an approaching front tightens the gradient between it and a ridge near the Big Island. The front is expected to stall as it moves over Kauai and Oahu tonight/Wednesday, with moderate N to NE winds developing behind the front. A ridge over Big Island and Maui waters will support light and variable winds.
Moisture along the stalled front will combine with a developing low aloft to bring the potential for some locally heavy downpours and isolated thunderstorms as the island atmosphere becomes increasingly unstable from late Wednesday into the weekend. High pressure building N of the islands will support moderate to locally strong NE to E trade winds from Wednesday night into Friday. Long term guidance favors a continued trade wind flow through next weekend.

Fire weather

No critical fire weather conditions are expected through the week due to increasing moisture and rain chances associated with a front forecast to move into the area and stall Tuesday through midweek.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 PM HST Thursday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kona, Kohala, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala, Big Island South.
Small Craft Advisory until 6 PM HST Thursday for all Hawaiian waters except Maalaea Bay,

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