Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 83 near the shore to around 71 above 3000 feet. East winds around 10 mph. Chance of rain 40 percent.

Tonight: Cloudy. Scattered showers in the evening, then showers and isolated thunderstorms after midnight. Lows around 67 near the shore to around 58 above 3000 feet. East winds around 10 mph in the evening becoming light. Chance of rain 90 percent.

Thursday: Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 80 near the shore to around 68 above 3000 feet. Southeast winds around 10 mph. Chance of rain near 100 percent.

South Kaua’i

Today: Partly sunny with scattered showers. Highs 79 to 85. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Cloudy. Numerous showers in the evening, then showers and isolated thunderstorms after midnight. Lows around 67. East winds around 10 mph. Chance of rain 90 percent.

Thursday: Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 76 to 82. East winds around 10 mph. Chance of rain near 100 percent.

Kaua’i Mountains

Today: Mostly cloudy with scattered showers. Highs 72 to 79 in the valleys to around 63 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Numerous showers in the evening, then showers and isolated thunderstorms after midnight. Lows 61 to 66 in the valleys to around 56 above 4000 feet. East winds 10 to 15 mph. Chance of rain near 100 percent.

Thursday: Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 69 to 76 in the valleys to around 60 above 4000 feet. Southeast winds around 10 mph. Chance of rain near 100 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 74 to 83. East winds around 10 mph. Chance of rain 50 percent.

Tonight: Cloudy. Scattered showers in the evening, then showers and isolated thunderstorms after midnight. Lows 61 to 69. Southeast winds around 10 mph. Chance of rain 90 percent.

Thursday: Showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible. Highs 71 to 80. Southeast winds around 10 mph. Chance of rain near 100 percent.

East Kaua’i

Today: Partly sunny with scattered showers. Highs 72 to 82. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Scattered showers in the evening, then showers and isolated thunderstorms after midnight. Lows 61 to 72. East winds around 10 mph. Chance of rain near 100 percent.

Thursday: Showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 68 to 80. Southeast winds around 10 mph. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

Light to moderate trades will focus showers over windward zones. Interior showers may develop over sheltered and leeward areas this afternoon. Expect bouts of heavy rainfall over Kauai and possibly Oahu Thursday through Friday. Isolated thunderstorms are also possible. Moderate trade flow will return from Sunday onward.

Discussion

Low pressure far northeast of the main Hawaiian Islands continues to put a big dent in the subtropical ridge which normally drives trade wind flow across the islands. The result is weaker flow like what we saw overnight. Light to moderate trades will allow development of a hybrid land and sea breeze pattern today and tonight. Aloft, the subtropical jet is pushing an area of thick high clouds across the Big Island and the islands of Maui County this morning. Broken to overcast low clouds linger across mauka sections of Kauai and Oahu, with the view of low clouds obscured by thick high clouds farther to the east.
Models show an upper trough northwest of the islands will dig southeastward over the next few days, developing into an upper low which will move across Kauai late Friday before filling. Light to moderate southeasterly flow and weak surface troughing beneath the upper low will enhance rainfall across the western islands Thursday through Friday. Isolated thunderstorms may also occur. As a result, a Flood Watch remains in effect for the islands of Niihau, Kauai and Oahu Thursday through Friday.
By Sunday, a rapidly weakening upper low will have moved east of the islands and surface ridging will have rebounded with the lifting of low pressure northeast of the islands farther northward. Moderate trade flow will build westward across the islands from Sunday into next week. Weak ridging aloft will stabilize our airmass, limiting total rainfall from Sunday onward.

Aviation

Light to moderate easterly trades will continue, with clouds and showers favoring the typical windward and mauka locations. The exception will be over sheltered leeward locations where sea breezes develop this afternoon. Expect brief periods of MVFR CIGS/VSBYS in and around showers, and AIRMET Sierra can't be ruled out through the early morning hours for N thru E sections of each island.

Marine

Gentle to locally fresh trade winds are being driven by a surface ridge 200 nm northeast of the state. Winds will begin to veer southeasterly tonight as the ridge erodes and a surface trough develops several hundred miles west of Kauai. Gentle to moderate southeasterly winds will prevail late tonight through Friday and bring chances for thunderstorms, mainly around Kauai and Oahu. The surface trough will dissipate on Saturday, leading to a return of the trade winds and Small Craft Advisory conditions around the Big Island and Maui.
A small, medium-period north swell will decline through today, followed by a small, short-period reinforcing swell late tonight and Thursday. Some of this swell will wrap into exposed eastern shores, but otherwise, east shore surf will be below May average as the nearby trade wind flow will be weaker than normal into Saturday. A small northwest swell is possible early next week, while returning trade winds will increase east shore surf.
Generally background swell from the southwest and southeast will maintain surf below May average through the next few days. Little source for southerly swell is seen beyond the weekend.

HFO Watches/Warnings/Advisories

Flood Watch from Thursday morning through Friday afternoon for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward.
Wind Advisory until 6 AM HST Friday for Big Island Summits.

Data Courtesy of NOAA.gov