Kauai Weather Forecast for September 21, 2024: Kauai Now

West Kaua’i

Today: Mostly sunny. A few scattered showers in the morning, then isolated showers in the afternoon. Highs are around 89 near the shore to around 77 above 3,000 feet. Northeast winds up to 15 mph. 50 percent chance of rain.

This evening: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 73 near the shore to around 61 above 3,000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Sunday: Mostly sunny with a few isolated showers. Highs around 89 near the shore to around 77 above 3,000 feet. Northeast winds up to 15 mph. Rain chance 20 percent.

South Kaua’i

Today: Partly sunny. Windy. Lots of showers in the morning, then scattered showers in the afternoon. Highs around 86. Northeast winds 10 to 20 mph. 70 percent chance of rain.

This evening: Wind. Mostly cloudy with scattered showers. Lows of 69 to 75°F. Northeast winds 10 to 20 mph. 50% chance of rain.

Sunday: Partly sunny. Lots of showers in the morning, then scattered showers in the afternoon. Highs around 86. Northeast winds 10 to 15 mph. 70 percent chance of rain.

Kaua’i Mountains

Today: Mostly cloudy. Frequent showers in the morning, then scattered showers in the afternoon. Highs 76 to 83 in the valleys to about 67 above 4,000 feet. East winds up to 15 mph. Chance of rain 80 percent.

This evening: Mostly cloudy. Windy. Numerous showers in the evening, then frequent after midnight. Lows 61 to 67 in the valleys to around 56 above 4,000 feet. East winds up to 20 mph. 80 percent chance of rain.

Sunday: Mostly cloudy. Frequent showers in the morning, then scattered showers in the afternoon. Highs 76 to 83 in the valleys to about 67 above 4,000 feet. East winds up to 15 mph. Chance of rain 80 percent.

North Kauai

Today: Partly sunny with scattered showers. Highs of 79 to 88. East winds up to 15 mph. 50 percent chance of rain.

This evening: Mostly cloudy. Scattered showers in the evening, then numerous after midnight. Minimum temperatures of 18 to 23 °C. Winds from the east of 16 to 24 km/h. Chance of rain of 70%.

Sunday: Partly sunny with scattered showers. Highs of 79 to 88. East winds up to 15 mph. 50 percent chance of rain.

East of Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. High temperatures 79 to 87. Northeast winds 10 to 15 mph. 70 percent chance of rain.

This evening: Mostly cloudy. Scattered showers in the evening, then numerous after midnight. Low temperatures 62 to 77. Northeast winds 10 to 15 mph. 70 percent chance of rain.

Sunday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. High temperatures 79 to 87. Northeast winds 10 to 15 mph. 70 percent chance of rain.

Synopsis

Breezy easterly trade winds will continue today, then ease briefly to a light to moderate range Sunday into Monday as the surface ridge weakens to the north. Showers will primarily favor windward and mauka areas, although a few may reach leeward and inland areas as an upper-level disturbance drifts southward over the region Sunday. Breezy trade winds and more settled conditions are expected to return Tuesday, persisting into the second half of next week.

Discussion

The forecast remains consistent, showing breezy easterly trade winds holding today as the surface ridge remains well to the north of the state. Satellite imagery shows good low cloud cover over and upwind of the islands (likely due to a weak mid-level trough in the area), which has enhanced the coverage of windward and mauka showers this morning. Rainfall totals over the past six hours (ending at 2 a.m. HST) have generally remained less than a tenth of an inch, with peak accumulations near three-quarters of an inch. Expect this trend to continue through the morning hours today, with mostly light showers.
A slight change in pattern is expected tonight through Monday, with upper levels subsidence in response to a broad, weak upper low drifting southward across the region, while the surface ridge weakens. Lighter trade winds, combined with a weakening subsidence inversion, could lead to an increase in wind showers, some of which will spread into leeward and inland areas or develop over leeward areas due to localized sea breezes in the afternoon. The best chances for thunderstorms will remain in the northern part of the state, where better mid-level fall rates and deeper moisture are expected.
Upper levels will increase Monday night through midweek as the upper low fills and lifts. This, combined with the rebuilding of the surface ridge to the north, will promote a return to a more stable and windy trade wind pattern. Although confidence is low at this point, some models are suggesting an area of ​​deeper tropical moisture associated with a disturbance passing far to the south of the state cutting off portions of the area late next week. Expect a wetter trade wind pattern for these areas should this materialize.

Aviation

An upper-level low is expected to move over the state over the weekend. Strengthened SHRAs are expected primarily over windward and mauka areas, with limited spillover to leeward areas. MVFR conditions can be expected with isolated IFR conditions within stronger prolonged SHRAs. VFR is generally expected to prevail outside of SHRA activity.
No AIRMET is in effect. The Sierra AIRMET may be required for mountain observations in windy areas overnight through this weekend.

Marine

A ridge of high pressure far north of Hawaii will keep fresh to strong easterly trade winds in today’s forecast. A cold frontal system moving across the far northern central Pacific basin will weaken the ridge Sunday through Monday, briefly dampening trade wind speeds to the mild to moderate range. A Small Craft Safety Advisory (SCA) remains in effect for windier waters around Maui County and the Big Island. This advisory will likely diminish Sunday and Monday as trade winds briefly weaken. Fresh to strong trade winds are expected to return by Tuesday of next week, and trade winds could approach SCA thresholds for our typical windier waters on the same eastern islands.
Waves along north and west-facing coasts will increase starting next Tuesday in response to a gale blowing east across the International Date Line near the Aleutian Islands this weekend and then into the Gulf of Alaska early next week. Forecasts show this northwest swell peaking locally Tuesday night into Wednesday from the northwest, then tapering off Thursday into Friday as it moves to a more north-northwest direction.
Surf along south facing shores will remain light throughout the weekend, with mainly a mix of long period southwesterly groundswells and short period southeasterly swells. An increasing trend is possible from Tuesday to midweek due to the arrival of a slightly stronger southwesterly swell.
Waves along east-facing coasts will remain small and choppy today, then diminish Sunday through next week as trade winds diminish locally and upstream across the eastern Pacific.

HFO Alerts/Warnings/Advisories

Small Craft Advisory until 6:00 p.m. HST tonight for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Leeward Waters of Big Island and Southeast Waters of Big Island.

Data courtesy of NOAA.gov