West Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 69 near the shore to around 59 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Highs 82 to 88 near the shore to around 73 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Thursday Night: Partly cloudy with isolated showers. Lows around 69 near the shore to around 60 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows around 70. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 79 to 87. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows around 70. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Numerous showers in the evening, then occasional showers after midnight. Lows 61 to 68 in the valleys to around 57 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain near 100 percent.

Thursday: Mostly cloudy. Occasional showers in the morning, then scattered showers in the afternoon. Highs 73 to 79 in the valleys to around 63 above 4000 feet. East winds 10 to 15 mph. Chance of rain 90 percent.

Thursday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 61 to 69 in the valleys to around 58 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Mostly cloudy with numerous showers. Lows 63 to 71. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 70 percent.

Thursday: Partly sunny with numerous showers in the morning, then mostly sunny with scattered showers in the afternoon. Highs 74 to 84. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Thursday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 71. East winds 10 to 15 mph. Chance of rain 60 percent.

East Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 73. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Thursday: Partly sunny with scattered showers. Highs 71 to 83. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Thursday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 64 to 73. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Locally breezy trade winds will persist through early next week as high pressure remains far north of the state. Somewhat active showers will continue across windward and mauka areas into the weekend. The gusty trades will carry brief showers over most leeward areas, while the leeward slopes of the Big Island experience spotty showers mainly in the afternoon and evening.

Discussion

A somewhat active shower pattern continues within the locally breezy trade wind flow. Persistent robust surface high pressure centered about 1200 miles to the northwest has the islands locked within a locally breezy and gusty trade wind flow, and broad upper-level troughing over the region has weakened and elevated the inversion, supporting a field of shower-bearing cumulus over and 500 miles east of the state. A loosely organized area of moisture within this cloud field moved over last night and this morning, producing roughly one quarter to three quarters of an inch of rainfall over wetter windward and mauka locales. The gusty winds periodically carried some rainfall over leeward areas from Kauai to west Maui, but accumulations were well below a tenth of an inch. The leeward slopes of the Big Island are transitioning toward a more summerlike pattern of spotty showers, some briefly heavy, during the midday through evening hours, followed by diminished rainfall overnight.
Breezy and somewhat wet trade winds will persist through at least Friday as additional pockets of moisture move through and the weak uper-level trough keeps the inversion elevated. A ridge aloft will develop over the region during the weekend, bringing an increase in stability. The GFS and ECMWF are suggesting that a band of moisture drifting in from the northeast could keep windward rainfall more active over windward Kauai and Oahu, but the increasingly stable conditions may limit leeward rainfall, even as the trades remain breezy and gusty. Typical trade wind weather looks to continue into early next week.

Aviation

Moderate to locally breezy trades will continue through the next several days and generally focus clouds and showers over windward areas. Periods of MVFR ceilings and visibilities will be possible as showers increase this evening through early Thursday. Otherwise, VFR conditions are expected to prevail.
AIRMET Tango remains in effect for moderate low-level turbulence over and immediately SW through NW of all island mountains due to the locally breezy trade winds. This AIRMET will likely continue for the next few days. In addition, AIRMET Sierra for mountain obscuration across north through east sections of the islands may be needed later tonight into early Thursday as showers increase.

Marine

Fresh to strong trades will persist through the weekend as a surface ridge remains north of the islands. A Small Craft Advisory will persist each day for the typical windier waters and channels around Maui County and the Big Island.
Surf along north and west-facing shores will remain up around average through Thursday due to a medium-period northwest swell that filled in Tuesday afternoon. This swell will gradually shift out of the north over the next couple of days.
Surf along south-facing shores will remain below average through Friday. A fresh long-period south- southwest swell is expected to arrive over the weekend, bringing an upward trend with above- average surf. Forerunners should begin filling in Friday, with the swell peaking late Saturday through Sunday. This swell has peaked slightly above guidance at the American Samoan buoy, which will translate to a peak locally late Saturday into Sunday.
Surf along east-facing shores will remain rough and choppy, with heights around average into the second half of the week. Heights could dip below average by the weekend due to a weakness forming in the ridge northeast of the area, leading to the upstream trades diminishing. A return to average levels is expected later this weekend and into early next week as the trades strengthen upstream.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Friday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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