West Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 69 near the shore to around 58 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers. Highs around 83 near the shore to around 73 above 3000 feet. Northeast winds up to 15 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

Wednesday Night: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 68 near the shore to around 58 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 67 to 72. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 85. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Wednesday Night: Breezy. Mostly cloudy with scattered showers. Lows around 69. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Numerous showers in the evening, then occasional showers after midnight. Lows 60 to 67 in the valleys to around 57 above 4000 feet. East winds up to 15 mph. Chance of rain 90 percent.

Wednesday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 78 in the valleys to around 63 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Wednesday Night: Breezy. Numerous showers in the evening, then frequent showers after midnight. Lows 60 to 67 in the valleys to around 56 above 4000 feet. East winds up to 20 mph. Chance of rain near 100 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 62 to 71. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 74 to 83. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 62 to 71. East winds 10 to 15 mph. Chance of rain 70 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 62 to 72. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 71 to 82. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 62 to 72. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

An upper trough will slide from north of the state to the east through Wednesday before settling northeast of the area. Moderate to fresh trade winds will continue to funnel in clouds and showers that will be enhanced by the upper trough over the next several days.

Discussion

An upper trough north of Hawaii will dive southeastward through Wednesday. The trough will form a cutoff low and become stationary around 600 miles northeast of Hawaii through Friday night before shifting away this weekend. Meanwhile, moderate to fresh trade winds continue at the surface. Current visible satellite shows cloud build ups across East Maui and Big Island and partly clouds elsewhere where trades are blowing this afternoon. Radar shows heavy showers popping up across the Big Island due to sea breeze convergence and instability from the upper trough. Expect these showers to wane around sunset. 00Z soundings show no inversion present with with a narrow band of CAPE to the equilibrium level at both Hilo and Lihue. Precipitable water values are average 1.2 to 1.3 inches.
Instability generated by the cold pool aloft will enhance showers and bring a slight chance of thunderstorms on the Big Island again Wednesday afternoon. Windward showers will see the highest activity during the overnight to early morning hours.
The upper low northeast of the islands will keep inversion and cloud heights elevated, allowing periods of showers to continue through the second half of the week. Only subtle day to day changes in island weather patterns are expected. This wet trade wind pattern may linger into the first half of next week as a shallow cold front and upper level trough approach the islands from the northwest.

Aviation

Whilst undergoing modest strengthening into tomorrow, locally breezy trades continue to deliver showers windward and mauka. Isolated MVFR possible within heavier showers, but VFR prevails, except perhaps Windward Big Island where observational trends and the latest guidance suggest a greater coverage of showers and MVFR potential tonight.
AIRMET Sierra may be needed for Windward Big Island tonight.
AIRMET Tango for lee turb may be needed as early as Wednesday afternoon as trades strengthen.
No AIRMETs in effect.

Marine

Moderate to fresh east-northeast trades will continue tonight before strengthening on Wednesday as a weak trough shifts to the west and a ridge builds north of the state. A Small Craft Advisory (SCA) has been issued for the typically windier waters surrounding Maui County and the Big Island beginning Wednesday morning. The SCA is likely to be extended through at least Friday before a trough approaches from the northwest this weekend, which will lead to a period of more relaxed trade winds.
Offshore buoys continue to show the new northwest swell around or below 1 ft. As a result, surf along north and west facing shores will remain small tonight before a small bump is possible on Wednesday. An upward trend is then expected during the second half of the week as another northwest swell arrives as early as Wednesday night. This swell originates from a storm-force low that tracked into the Bering Sea this past weekend, as confirmed by scatterometry. Therefore, this swell appears more likely to materialize. Looking further ahead, a storm-force low east of Japan will send a moderate, longer-period northwest swell toward the islands for Friday and Saturday, with surf heights potentially approaching advisory levels along exposed north and west facing shores.
Surf along south-facing shores will remain small through much of the week, with mainly background south to southwest swell expected. Another south-southwest pulse may arrive by this weekend from recent activity within our swell window east of New Zealand, providing a small increase in surf.
Surf along east-facing shores will remain relatively small and choppy through midweek, with a slight rise possible Thursday and Friday as trades strengthen.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov