West Kaua’i

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Haze through the night. Lows 66 to 71 near the shore to around 59 above 3000 feet. Light winds. Chance of rain 40 percent.

Tuesday: Partly sunny with scattered showers. Haze. Highs 80 to 86 near the shore to around 71 above 3000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Haze through the night. Lows 66 to 71 near the shore to around 59 above 3000 feet. Light winds. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Haze through the night. Lows around 68. Light winds becoming north around 10 mph after midnight. Chance of rain 40 percent.

Tuesday: Partly sunny with scattered showers. Haze. Highs 78 to 85. Northeast winds up to 10 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Haze through the night. Lows around 69. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 30 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Haze through the night. Lows 59 to 67 in the valleys to around 56 above 4000 feet. Light winds. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Haze through the day. Highs 72 to 78 in the valleys to around 63 above 4000 feet. Light winds. Chance of rain 70 percent.

Tuesday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Haze through the night. Lows 60 to 68 in the valleys to around 57 above 4000 feet. Light winds. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Haze through the night. Lows 62 to 70. West winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Haze. Highs 73 to 82. Northeast winds up to 10 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows 62 to 69. Light winds. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Haze through the night. Lows 62 to 72. Light winds. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Haze. Highs 71 to 84. North winds up to 10 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Haze through the night. Lows 62 to 73. Light winds. Chance of rain 40 percent.

Detailed Forecast

Synopsis

A moist unstable airmass will remain in place during the next couple of days, with sea breezes allowing for the development of locally heavy showers and a few thunderstorms each afternoon. Land breezes will keep most shower activity over the coastal waters or near the coast at night. Trade winds are expected to return Wednesday, reaching breezy levels Friday through the weekend, along with a more typical windward and mauka shower pattern.

Discussion

Currently at the surface, a weak trough of low pressure remains near Kauai, while high pressure is centered far northeast of the island chain. Winds remain light across the state, with sea breezes over most areas this afternoon. Visible satellite and radar imagery shows extensive clouds over island interiors with scattered showers, some heavy at times. Rainfall totals this afternoon have been generally in the quarter to half inch range over the western half of the state, where the inversion has been eroded and a pool of higher precipitable water values currently sits. The highest amounts so far have been along the Koolau Range on Oahu around one to one and a half inches in the last 3 hours. Rainfall on the eastern half of the island chain has been lighter due to the continued presence of a weak inversion and lower precipitable water.
The weak trough of low pressure will remain nearly stationary over the smaller islands through Tuesday. Winds will change little during this time, with land and sea breezes dominant over most of the state. The airmass will remain moist and unstable over the next few days as a deep upper low dives southward over the state. This will bring some locally heavy showers and a few thunderstorms to the island chain, particularly during the afternoon hours and favoring interior and leeward areas. The chance for heavy showers and thunderstorms will be most widespread on Tuesday as the center of the low (and greatest instability) is at it's closest approach. Land breezes will tend to push activity out over the coastal waters or areas near the immediate coast at night.
The surface troughing over the islands will gradually dampen out during the middle and latter part of the week as high pressure builds to the north. This should allow a gradual return and strengthening of the trade winds across the state around midweek, with the trades reaching breezy levels Friday through the weekend. The upper low will move off to the east of the islands during the second half of this week, with ridging firmly in place by week's end. This will allow for more stable conditions and a return to more typical trade shower pattern, with activity focusing mainly over windward and mauka areas through the weekend.
Volcanic emissions and light background southeast flow will keep vog in place over most of the state through Tuesday. The returning trades should clear the vog out of the smaller islands by late Wednesday.

Aviation

A weak surface trough slowly passing over the islands will keep the background wind flow light and variable for the next couple days. Sea breezes and inland cloudiness will prevail in the afternoon and early evening hours and weak land breezes and mostly clear skies in the late night and early morning hours.
A corresponding upper level low will generate air mass instability and encourage shower development statewide. Brief MVFR/IFR CIG or VIS are possible in showers. There remains a slight chance of thunderstorms through this evening and also tomorrow afternoon and evening.
No AIRMETs are currently in effect or anticipated at this time.

Marine

A trough of low pressure near Kauai will linger through Tuesday and continue to weaken the high pressure ridge over the eastern Hawaiian Islands, maintaining light and variable winds through Tuesday. This boundary combined with an upper level disturbance that will move overhead tonight into tomorrow, will increase the potential for showers and thunderstorms over the coastal and offshore waters. Trades will build back in from Wednesday onward as a high pressure system builds to the north of the main Hawaiian Islands. Trade winds should strengthen to Small Craft Advisory levels for the typical windy areas around Maui County and the Big Island late Thursday.
A small northwest swell will slowly fade into Tuesday. Surf along north and west facing shores should remain near or below average levels for this time of year. By Thursday, a moderate long period north-northwest swell is expected to arrive, producing surf above the seasonal average (6 feet for the month of May). This north- northwest swell will slowly decline over the weekend.
Multiple small south swells will maintain small background southerly energy through Tuesday. A bump up in south-southwest swell energy will arrive on Wednesday, peak Thursday producing moderate surf, and then slowly fade through the weekend. However, a mix of reinforcing south-southwest swell and new south-southeast swell energy will arrive this weekend and should help maintain surf near or above the summer average (5 feet). Then another pulse of south-southwest swell energy will arrive early next week.
Weak upstream trade wind flow will keep surf on the small side for east facing shores. An increase is expected by Wednesday as the trade winds return. Trade winds should strengthen on Friday with rough and choppy surf expected along east facing shores through the weekend.

HFO Watches/Warnings/Advisories

None.

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