West Kaua’i

Rest Of Tonight: Mostly cloudy. Frequent showers early in the evening. Isolated thunderstorms in the evening. Scattered showers in the late evening and overnight. Lows around 67 near the shore to around 58 above 3000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 90 percent.

Sunday: Mostly cloudy. Scattered showers in the morning. Isolated thunderstorms in the late morning and afternoon. Numerous showers in the afternoon. Highs 78 to 85 near the shore to around 70 above 3000 feet. Southeast winds up to 15 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy with frequent showers and isolated thunderstorms in the evening, then partly cloudy with scattered showers after midnight. Lows 64 to 69 near the shore to around 58 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 90 percent.

South Kaua’i

Rest Of Tonight: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Lows around 67. Northeast winds around 10 mph. Chance of rain 50 percent.

Sunday: Mostly cloudy. Scattered showers early in the morning, then scattered showers and isolated thunderstorms in the late morning and afternoon. Highs 76 to 84. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then numerous showers after midnight. Lows around 67. Northeast winds around 10 mph. Chance of rain 70 percent.

Kaua’i Mountains

Rest Of Tonight: Frequent showers and isolated thunderstorms in the evening, then scattered showers after midnight. Lows 58 to 67 in the valleys to around 56 above 4000 feet. Light winds. Chance of rain near 100 percent.

Sunday: Mostly cloudy. Scattered showers in the morning. Isolated thunderstorms in the late morning and afternoon. Numerous showers in the afternoon. Highs 71 to 76 in the valleys to around 61 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 70 percent.

Sunday Night: Frequent showers and isolated thunderstorms in the evening, then numerous showers after midnight. Lows 57 to 67 in the valleys to around 56 above 4000 feet. East winds up to 10 mph. Chance of rain near 100 percent.

North Kaua’i

Rest Of Tonight: Mostly cloudy. Frequent showers early in the evening. Isolated thunderstorms in the evening. Scattered showers in the late evening and overnight. Lows 61 to 68. Southeast winds up to 10 mph. Chance of rain 80 percent.

Sunday: Mostly cloudy. Scattered showers in the morning. Isolated thunderstorms in the late morning and afternoon. Numerous showers in the afternoon. Highs 72 to 81. Southeast winds up to 15 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy. Frequent showers and isolated thunderstorms in the evening, then numerous showers after midnight. Lows 60 to 67. Southeast winds up to 10 mph. Chance of rain 80 percent.

East Kaua’i

Rest Of Tonight: Frequent showers early in the evening. Isolated thunderstorms in the evening. Scattered showers in the late evening and overnight. Lows 61 to 71. Northeast winds up to 10 mph shifting to the northwest after midnight. Chance of rain near 100 percent.

Sunday: Mostly cloudy. Scattered showers in the morning. Isolated thunderstorms in the late morning and afternoon. Numerous showers in the afternoon. Highs 69 to 81. East winds up to 15 mph. Chance of rain 70 percent.

Sunday Night: Frequent showers and isolated thunderstorms in the evening, then numerous showers after midnight. Lows 61 to 71. East winds up to 10 mph in the evening becoming light. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

Trade winds will strengthen into Sunday, while a deep low pressure system to the west bring instability and enhancement to the incoming showers. Isolated thunderstorms and locally heavy rainfall will be possible statewide, but most of the widespread coverage will remain north of the state. Stability will return early next week with trade winds focusing showers windward and mauka.

Discussion

A deep low pressure system is positioned west northwest of the main Hawaiian islands this afternoon, and will be the cause of some active weather over the next few days. At the surface, high pressure north of the associated low is beginning to nose in from the east side of it and will allow trade winds to strengthen Sunday into next week as it sets up far northeast of the area. Winds will veer slightly southeasterly due to the low to the west northwest.
Moderate to locally heavy showers in a band connected to the surface low will linger just north of the state over the next few days, with showers and possible thunderstorms along the southern fringes of the band impacting the state at times through at least Sunday. The ingredients and the greatest focus just to the north of the islands do not push confidence high enough for the issuance of a Flood Watch, though the situation will need monitoring.
The GFS and ECMWF show the chances for rainfall declining by late Sunday or Monday. The upper low will weaken and broaden out and while the surface low weakens and tracks away to the west. Trade winds will push lingering and upstream moisture across the islands for the first half of the week resulting in lighter and less frequent showers focused windward and mauka showers. Trade winds and windward and mauka showers expected into the second half of the week as well.

Aviation

Light to moderate east southeast winds with localized land/sea breezes can be expected this weekend as a surface low and trough linger to the west of the Hawaiian Islands. There is also some marginal instability due to broad upper level troughing. Thus, expect isolated to scattered showers to affect mainly windward areas, with localized sea breezes leading to isolated to scattered showers over leeward locations as well. Brief MVFR ceilings and visibility will be possible in some of the heavier showers.
Enough instability will be present this evening and tonight to introduce a slight chance of thunderstorms to windward portions of the smaller islands.
AIRMET Sierra is in effect for mountain obscuration for northern and western portions of Kauai and Oahu and could be expanded to include other islands.

Marine

Fresh to moderate trades will veer slightly east-southeast over the western half of the state as an area of low pressure meanders northwest of the state into early next week. Isolated thunderstorms will be possible through Sunday night, mainly over the waters north of the islands, due to the proximity of the low. The low is expected to gradually weaken through early next week as a high passes north of state, which may generate fresh to locally strong easterly winds over the eastern half of the state, requiring a Small Craft Advisory (SCA), while the western half remains in moderate to locally fresh east-southeast flow. The low is expected gradually drift west and weaken further early next week, allowing winds to shift back to a more typical easterly direction and increase to fresh to locally speeds statewide by Tuesday night and hold through the second half of next week.
A moderate, west-northwest (300-320) swell will continue to trend down through the rest of the weekend. The High Surf Advisory has been cancelled as surf heights have dropped below advisory levels. A small to moderate, medium-period north-northwest swell (340-350) may overlap the fading west-northwest swell Sunday night into Wednesday. In the long range, a series of small, long-period northwest (320-330) swells look to keep surf from going flat through much of next week.
Rough choppy surf along east facing shores will drop a notch into early next week. As winds strengthen by midweek, expect east shore surf to pick back up. No significant south swells expected through next week.

HFO Watches/Warnings/Advisories

Wind Advisory until 8 AM HST Sunday for Big Island Summits.

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