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

East southeast winds will ease tonight, with daytime sea breeze and nighttime land breeze pattern from Wednesday and continuing 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

At the surface, a 1025 mb surface high is centered far northeast of Hawaii driving gentle to moderate east southeast winds across the area. An approaching cold front is located around 650 miles northwest of Kauai, while an approaching weak trough is located 300 miles east of the Big Island.
Winds will taper off and veer southeasterly tonight as the front and trough converge towards the islands. Land breezes will keep most of the associated clouds and showers with both features offshore, but as sea breezes build in during the day Wednesday, clouds and showers will focus over the islands.
An upper trough will dig southeasterly across the islands late Wednesday night through Friday. The front will merge with the surface trough creating a pool of low level moisture over the state. As the upper trough moves through, 500 mb temperatures will lower to around -12 to -13C and precipitable water values will increase from around 1.2 currently to around 1.5 inches on Thursday. This will likely result in some heavier showers and a slight chance of thunderstorms Thursday and Friday (more of the focus will be on Big Island Friday). Possible minor ponding/flooding resulting from this rainfall, but holding off with a Flood Watch for now given the brief window of upper level forcing. Snow will be possible on the Big Island summits Thursday through Friday and will consider a Winter Weather Advisory. The upper trough will weaken and slide east of the state by late Friday returning to more a more stable atmosphere.
Light to moderate trade winds will gradually nose in over the weekend, with likely wetter-than-normal windward and mauka showers before the area of moisture is cleared to the west. A more typical trade wind pattern may slowly return over the weekend into early next week.

Aviation

Moderate trades will gradually ease into tomorrow and usher in SHRA and low cigs to windward and mauka locations. However, winds may begin to be light enough to see some sea breeze development that would bring some isol SHRA to leeward areas. MVFR conds will be possible in any SHRA, but VFR should 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

Trade winds will continue to decline and shift out of the southeast through Wednesday as an advancing front weakens the surface ridge north of the state. Easterly trade winds are currently at moderate to fresh strength, and a morning ASCAT pass confirmed that winds around the Big Island have eased enough to allow the Small Craft Advisory (SCA) to be dropped. By Wednesday morning, gentle to moderate east to southeasterly winds will prevail statewide, followed by a brief period of variable winds around Kauai and possibly Oahu Wednesday afternoon and evening. Gentle to locally fresh east to east-southeast trade winds will dominate Thursday and Friday, and a slight increase in winds may require the SCA to be reissued around the Big Island and Maui during the weekend.
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.
Small 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 and will push surf near High Surf 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 tonight 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.

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