West Kaua’i

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Lows 62 to 67 near the shore to around 53 above 3000 feet. Light winds becoming northeast up to 10 mph after midnight. Chance of rain 50 percent.

Thursday: Mostly cloudy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Haze through the day. Locally heavy rainfall possible in the afternoon. Highs around 83 near the shore to around 73 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 70 percent.

Thursday Night: Mostly cloudy with scattered showers and isolated thunderstorms in the evening, then partly cloudy with isolated showers and thunderstorms after midnight. Haze through the night. Lows 62 to 67 near the shore to around 53 above 3000 feet. Light winds becoming northeast up to 10 mph after midnight. Chance of rain 50 percent.

South Kaua’i

Tonight: Mostly cloudy. Haze in the evening. Scattered showers and isolated thunderstorms in the evening, then numerous showers and isolated thunderstorms after midnight. Lows 60 to 66. Light winds. Chance of rain 70 percent.

Thursday: Haze in the morning. Mostly cloudy with numerous showers and isolated thunderstorms. Locally heavy rainfall possible in the afternoon. Highs around 81. East winds around 10 mph. Chance of rain 70 percent.

Thursday Night: Mostly cloudy. Numerous showers and isolated thunderstorms in the evening, then scattered showers and isolated thunderstorms after midnight. Lows 60 to 66. Northeast winds around 10 mph. Chance of rain 60 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Lows around 56 in the valleys to around 48 above 4000 feet. Light winds. Chance of rain 50 percent.

Thursday: Occasional showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Haze through the day. Locally heavy rainfall possible in the afternoon. Highs around 76 in the valleys to around 65 above 4000 feet. Light winds. Chance of rain near 100 percent.

Thursday Night: Mostly cloudy. Numerous showers and isolated thunderstorms in the evening, then scattered showers and isolated thunderstorms after midnight. Haze through the night. Lows around 56 in the valleys to around 48 above 4000 feet. Light winds becoming east around 10 mph after midnight. Chance of rain 70 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers and isolated thunderstorms. Lows 56 to 65. Light winds. Chance of rain 50 percent.

Thursday: Mostly cloudy. Haze in the morning. Occasional showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 76 to 82. Southeast winds up to 10 mph. Chance of rain 90 percent.

Thursday Night: Mostly cloudy. Haze in the evening. Numerous showers and isolated thunderstorms in the evening, then scattered showers and isolated thunderstorms after midnight. Lows 56 to 65. East winds up to 10 mph. Chance of rain 70 percent.

East Kaua’i

Tonight: Mostly cloudy with numerous showers and isolated thunderstorms. Haze after midnight. Lows 54 to 67. Light winds. Chance of rain 70 percent.

Thursday: Mostly cloudy. Haze in the morning. Occasional showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 74 to 80. Light winds becoming east around 10 mph in the afternoon. Chance of rain 90 percent.

Thursday Night: Mostly cloudy. Numerous showers and isolated thunderstorms in the evening, then scattered showers and isolated thunderstorms after midnight. Lows 54 to 67. East winds around 10 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

An approaching front from the northwest is pushing a ridge over the islands, resulting in light winds over the islands. This afternoon's sea breezes will become overnight land breezes. Some clearing of clouds is possible overnight, particularly over Maui County and the Big Island. An upper level disturbance will bring clouds and showers to the island tonight through Friday with the possibility for heavier showers and thunderstorms.

Discussion

As expected, there have been tweaks to the forecast with the afternoon package. The overall forecast philosophy remains the same with showers increasing in coverage tonight. Thunderstorms are possible mainly west of Molokai starting tonight, and spreading statewide tomorrow. By Friday night, the chance of thunderstorms is shifted to Maui County and the Big Island. Have in general increased QPF, leaning into the National Blend of Models (NBM) values.
The front to the northwest of Kauai continues to weaken, and continues to keep a ridge nearby, resulting in the light winds over the islands. The front is expected to continue to stay to the west of Kauai and weaken over the next 12 to 24 hours. The surface ridge nearby will continue to bring the light winds to the region. Meanwhile, an upper level trough over the islands will dig in, bringing colder upper level temperatures. This coupled with an increase in precipitable water will provide sufficient instability over the islands that will result in an increase in showers, and bring the possibility for heavier showers and thunderstorms.
Models are in good agreement with 500 mb temperatures reaching around -13C, and with precipitable water values reaching around 1.5 inches, both of which are below normal for April. With no organized surface feature moving over the islands to focus the showers, confidence remains low for any widespread flooding. As a result, we are not issuing a Flood Watch, but cannot rule out localized flooding during the event.
The upper level trough moves to the east Saturday, with a more typical trade wind pattern setting up at the surface for the weekend and into Monday. Heading into Tuesday, the global models are depicting another upper level low sinking southward as a front once again approaches from the northwest. This could lead to another round of wet weather for the middle of the new week.

Aviation

Wind speeds are on the decline as an approaching front stalls NW of the islands. Light and variable winds will prevail over Kauai and Oahu while light to moderate ESE flow will likely persist over Maui and the Big Island. VFR conditions will prevail, and no AIRMETs are currently posted, but the island atmosphere will become increasingly unstable over the next 12-24 hours as a sharp trough aloft passes overhead. The trough will bring the potential for localized IFR CIG/VIS in +TSRA/+SHRA, as well as moderate to severe turbulence aloft.

Marine

The slow approach of a weakening cold front into the far northwest offshore waters today has weakened nearshore east- southeast winds. As this front stalls just west of the islands Thursday, western water light and variable breezes around Kauai will become more localized daytime onshore and overnight offshore breezes. Elsewhere, gentle to moderate east southeast winds will persist over smaller island windward waters and around Big Island the next few days. As surface high pressure strengthens far northeast of the state, a brief return to fresh to locally strong easterly trades is possible this weekend. There will be an increased chance for widespread heavy showers and thunderstorms from tonight through Friday in response to the passage of an upper level trough over the state.
Surf along exposed north and west-facing shores will continue to diminish today as the latest northwest swell fades away. An upward trend in surf is expected through the day Thursday as a newly- arriving moderate size, medium period north northwest swell builds down the island chain. North and west shore surf may near advisory levels Thursday night into Friday during the peak of this swell. A downward trend is expected as the swell turns out of the north this weekend.
East-facing shore chop will remain low into Saturday. A slight uptick in trades will result in a steady rise of eastern wind waves early next week.
Surf along south-facing shores will remain small through the week with the passing of overlapping background south swells. A larger south southwest swell may arrive next Tuesday.

HFO Watches/Warnings/Advisories

None.

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