West Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 64 to 69 near the shore to around 55 above 3000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Wednesday: Mostly cloudy with scattered showers. Highs around 85 near the shore to around 75 above 3000 feet. South winds up to 10 mph. Chance of rain 50 percent.

Wednesday Night: Cloudy. Scattered showers until early morning, then scattered showers and slight chance of thunderstorms early in the morning. Haze through the night. Lows 62 to 67 near the shore to around 53 above 3000 feet. Light winds. Chance of rain 50 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 62 to 68. Northeast winds up to 10 mph. Chance of rain 40 percent.

Wednesday: Mostly cloudy with scattered showers. Highs around 83. East winds up to 10 mph shifting to the south around 10 mph in the afternoon. Chance of rain 50 percent.

Wednesday Night: Cloudy. Scattered showers until early morning, then scattered showers and slight chance of thunderstorms early in the morning. Haze through the night. Lows 60 to 66. Light winds. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with scattered showers. Lows around 58 in the valleys to around 50 above 4000 feet. Light winds. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 78 in the valleys to around 67 above 4000 feet. Light winds. Chance of rain 70 percent.

Wednesday Night: Cloudy. Haze through the night. Numerous showers early in the evening. Scattered showers in the late evening and overnight. Slight chance of thunderstorms early in the morning. Lows around 56 in the valleys to around 48 above 4000 feet. Light winds. Chance of rain 70 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 58 to 67. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Wednesday: Mostly cloudy with scattered showers. Highs 78 to 84. Light winds. Chance of rain 50 percent.

Wednesday Night: Cloudy. Scattered showers until early morning, then scattered showers and slight chance of thunderstorms early in the morning. Haze through the night. Lows 56 to 65. Light winds. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 56 to 69. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Wednesday: Mostly cloudy with scattered showers. Highs 76 to 82. Southeast winds up to 10 mph. Chance of rain 50 percent.

Wednesday Night: Cloudy. Scattered showers until early morning, then scattered showers and slight chance of thunderstorms early in the morning. Haze through the night. Lows 54 to 67. Light winds. Chance of rain 50 percent.

Detailed Forecast

Synopsis

The trade winds will continue to ease tonight, with a daytime sea breeze and overnight land breeze pattern setting up Wednesday through Friday. A disturbance aloft moving over the islands could bring some heavier showers and thunderstorms Thursday and Friday. A return to a more typical trade wind regime along with a gradual increase in trade wind speeds will be possible over the weekend into early next week.

Discussion

Currently at the surface, a cold front is located around northwest of Kauai, while a 1031 mb high is centered around 2250 miles north-northeast of Honolulu. The trades have eased through the day, and are now blowing at light to moderate speeds. Infrared satellite imagery shows partly to mostly cloudy conditions in place, while radar imagery shows showers scattered across the state. Main short term focus revolves around trade wind trends and rain chances.
A ridge to the north of the islands will gradually weaken and erode during the day or so, as a cold front approaches from the northwest. The trades will ease tonight, then become disrupted Wednesday, with sea breezes common over the western islands, while the trades shift east-southeasterly at light to moderate speeds over the eastern end of the state. The front will stall out northwest of the area Thursday, with broad troughing developing across the island chain. Land and sea breezes will remain common during this time, with background light to moderate east- southeast winds confined to areas around the Big Island. The trough appears to dampen Friday through the weekend, allowing a gradual return and strengthening of the trades which will continue into early next week.
As for the remaining weather details, the lingering daytime heating showers should continue to diminish over the next couple hours, while isolated to scattered showers continue to roll into windward areas through the night. A transition over to a convective pattern is expected Wednesday, with showers favoring the island interiors during the afternoon and evening hours, and areas near the coast at night. This pattern will linger into Friday when the trades will begin to return. Meanwhile, an upper level trough will move slowly eastward across the state Wednesday night into Friday, with 500 mb temperatures of -12 to -13C and precipitable water values increasing to around 1.5 inches. This will likely result in some heavier showers, particularly during the afternoon and evening hours. Isolated thunderstorms will also be possible as the cold pool aloft moves eastward across the state. A more typical trade wind pattern may slowly return late Friday through early next week.

Aviation

Moderate easterly trades will gradually veer and ease tonight through Wednesday continuing to bring the potential for SHRA and low cigs to windward and mauka locations. However, winds may begin to be light enough to see some sea breeze development as convergent boundaries may be another source of clouds and showers to leeward areas of some of the smaller islands. MVFR conditions will be possible in any showers, but overall, VFR conditions will prevail.
While the ongoing eruption of Kilauea is currently paused, there is degassing occurring. This could cause some hazy conds across the islands. It is not enough to impact vsbys at this time and not currently in any TAFs but was worth a mention.
No AIRMETs in effect.

Marine

Moderate to fresh trade winds will continue to ease and shift out of the east-southeast overnight through midweek as a front approaches and stalls northwest of the state. Over the western end of the islands, the weakening winds will allow a land and sea breeze pattern to develop near the coasts, which will persist into Friday. For the eastern end of the state, light to moderate east to southeast breezes, with localized fresh pockets, will likely persist, particularly around the Big Island. A return to fresh to strong easterly trades is possible by the weekend as the ridge reestablishes to the north.
As trades diminish, chances for heavy showers and thunderstorms will increase. The main threat will develop around Kauai and Oahu late Wednesday night, slowly spread to the entire island chain Thursday, then diminish from west to east on Friday.
Surf along exposed north and west facing shores will continue to lower through Wednesday as a northwest swell fades. A medium- period north-northwest swell will build Thursday, likely driving surf heights near advisory levels during the peak Thursday night and early Friday. This swell will steadily decline and shift out of the north later Friday and the weekend.
Surf along east facing shores will trend down into Wednesday as trades ease. East shore surf will remain below April average through at least Saturday and will likely rise to around average on Sunday.
Surf along south facing shores will remain small through most of the week, with mainly overlapping background south swells moving through. A larger pulse of south-southwest swell may arrive Tuesday.

HFO Watches/Warnings/Advisories

None.