West Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers and thunderstorms. Haze. Locally heavy rainfall possible after midnight. Lows around 69 near the shore to around 59 above 3000 feet. Light winds. Chance of rain 20 percent.

Sunday: Mostly cloudy. Isolated showers and thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Haze through the day. Locally heavy rainfall possible. Highs 80 to 86 near the shore to around 71 above 3000 feet. Light winds. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and isolated thunderstorms early in the evening, then scattered showers in the late evening and overnight. Haze through the night. Locally heavy rainfall possible early in the evening. Lows 65 to 70 near the shore to around 58 above 3000 feet. Light winds. Chance of rain 50 percent.

South Kaua’i

Tonight: Partly cloudy with isolated showers. Haze. Lows around 69. West winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Sunday: Mostly cloudy. Isolated showers and thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Haze through the day. Locally heavy rainfall possible. Highs 79 to 86. Light winds. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and isolated thunderstorms early in the evening, then scattered showers in the late evening and overnight. Haze through the night. Locally heavy rainfall possible early in the evening. Lows around 69. Light winds. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Partly cloudy with scattered showers and isolated thunderstorms in the evening, then mostly cloudy with isolated showers and thunderstorms after midnight. Haze through the night. Locally heavy rainfall possible after midnight. Lows 60 to 68 in the valleys to around 57 above 4000 feet. Light winds. Chance of rain 30 percent.

Sunday: Mostly cloudy. Scattered showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Haze through the day. Locally heavy rainfall possible. Highs 73 to 79 in the valleys to around 64 above 4000 feet. Light winds. Chance of rain 60 percent.

Sunday Night: Mostly cloudy. Scattered showers and isolated thunderstorms early in the evening, then scattered showers in the late evening and overnight. Haze through the night. Locally heavy rainfall possible early in the evening. Lows 59 to 68 in the valleys to around 57 above 4000 feet. Light winds. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy. Scattered showers and isolated thunderstorms in the evening, then isolated showers and thunderstorms after midnight. Haze through the night. Locally heavy rainfall possible after midnight. Lows 62 to 70. South winds up to 10 mph in the evening becoming light. Chance of rain 30 percent.

Sunday: Mostly cloudy with scattered showers and isolated thunderstorms. Haze. Locally heavy rainfall possible. Highs 74 to 83. Light winds. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and isolated thunderstorms early in the evening, then scattered showers in the late evening and overnight. Haze through the night. Locally heavy rainfall possible early in the evening. Lows 62 to 70. Light winds. Chance of rain 50 percent.

East Kaua’i

Tonight: Partly cloudy with isolated showers and thunderstorms. Haze. Locally heavy rainfall possible after midnight. Lows 62 to 72. Light winds. Chance of rain 20 percent.

Sunday: Mostly cloudy with scattered showers and isolated thunderstorms. Haze. Locally heavy rainfall possible. Highs 72 to 85. Light winds. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and isolated thunderstorms early in the evening, then scattered showers in the late evening and overnight. Haze through the night. Locally heavy rainfall possible early in the evening. Lows 62 to 72. Light winds. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light winds will prevail through early next week, allowing sea breezes to bring clouds and showers to leeward and interior areas each afternoon and land breezes to help clear out these areas overnight. Increasing moisture and a disturbance aloft will bring an increase in shower activity across the state Sunday through Tuesday. Some of these showers could be heavy and a few rumbles of thunder will also be possible. A return to more typical trade wind weather featuring mainly windward and mauka showers appears take hold Wednesday, with breezy conditions developing by Friday and continuing through next weekend.

Discussion

Currently at the surface, a weak diffuse trough of low pressure is located around 100 miles northwest of Kauai, while a 1029 mb high centered around 1600 miles northeast of Honolulu. Winds remain light across much of the state, with sea breezes beginning to give way to developing land breezes. Infrared satellite imagery shows partly to mostly cloudy conditions in place. Radar imagery shows a few decaying leeward/interior showers and a few showers moving into windward areas over the eastern end of the state. Elsewhere, dry conditions prevail. Main short term focus revolves around the potential for heavy rain and thunderstorms during the next few days.
The weak trough of low pressure will shift slowly eastward tonight and Sunday, then settle over the islands early next week. Winds will change little during this time, with land and sea breezes dominant over most of the state. The troughing over the islands will gradually dampen out during the middle and latter part of next week as high pressure builds to the north. This should allow a gradual return and strengthening of the trade winds across the state, with the trades reaching breezy levels Friday through next weekend.
As for the remaining weather details, the airmass over the islands will gradually moisten up tonight through Tuesday as a weak diffuse trough moves over the state. A land/sea breeze pattern will remain in place, with showers favoring interior and leeward areas during the afternoon and evening hours, and remaining mostly over the coastal waters or areas near the immediate coast at night. The airmass appears unstable enough Sunday afternoon, that some locally heavy downpours and a few rumbles of thunder will remain possible. The airmass will further destabilize Monday and Tuesday as a disturbance aloft dives southward over the state. This is expected to bringing a better chance for some locally heavy rainfall and a few thunderstorms to the island chain. A return to more typical trade wind weather featuring mainly windward and mauka showers appears take hold Wednesday, with this pattern then persisting through next weekend.

Aviation

A light flow pattern will allow for land breezes tonight, followed by seas breezes along coastal regions by Sunday afternoon. Conditions will become more unstable Sunday afternoon as an upper level trough drops southward over the islands. Thus, heavier showers and isolated thunderstorms will be possible from the afternoon through evening and produce MVFR ceilings and visibility or even brief periods of IFR conditions with some of the more robust activity.

Marine

A low pressure system northwest of Kauai continues to weaken the high pressure ridge over the Hawaiian Islands. A diffuse trough near the island of Kauai will bring some heavier showers and thunderstorms to the nearby coastal and offshore waters. This boundary is expected to slowly lift to the northeast over the next few days increasing the potential for showers and thunderstorms over the coastal and offshore waters. Light and variable winds will continue into the first half of next week. Trades will build back in from Wednesday onward as a high pressure system builds in north of the Hawaii Region.
A small long period northwest swell will peak tonight into Sunday, then fade through early next week. Surf along north and west facing shores should remain near or below average levels for this time of year. By Thursday, a medium long period north northwest swell is expected to enter the waters and produce surf that may approach advisory levels.
Multiple small early season south swells will maintain small background southerly energy through mid next week. A bump up in south swell energy is expected to arrive late Thursday and last through next weekend. Weak upstream trade wind flow will keep surf along east facing shores near or below seasonal averages.

HFO Watches/Warnings/Advisories

None.

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