West Kaua’i

Tonight: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 70 near the shore to around 60 above 3000 feet. East winds up to 20 mph becoming 10 to 15 mph after midnight. Chance of rain 50 percent.

Saturday: Breezy. Mostly sunny with isolated showers. Highs 83 to 89 near the shore to around 75 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Saturday Night: Partly cloudy. Lows around 70 near the shore to around 60 above 3000 feet. Northeast winds up to 15 mph.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 71. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 81 to 88. East winds 10 to 20 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with isolated showers. Lows around 70. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 61 to 69 in the valleys to around 59 above 4000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Saturday: Partly sunny with scattered showers. Highs 75 to 81 in the valleys to around 66 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 61 to 69 in the valleys to around 58 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 64 to 72. East winds up to 15 mph shifting to the southeast after midnight. Chance of rain 50 percent.

Saturday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 86. Southeast winds up to 15 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with isolated showers. Lows 63 to 72. Southeast winds up to 15 mph becoming around 10 mph after midnight. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 64 to 75. East winds 10 to 15 mph. Chance of rain 70 percent.

Saturday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 73 to 85. East winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 50 percent.

Saturday Night: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 64 to 75. Northeast winds up to 15 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

The high pressure ridge north of the Hawaiian Islands will weaken slightly on Sunday and Monday as a cold front stalls out northwest of the island chain. Trade wind speeds will decrease a bit during this time period. Wind speeds increase into the breezy range from Tuesday into Wednesday as the ridge builds in north of the state. Brief periods of showers remain in the forecast favoring the windward and mountain areas during the overnight to early morning hours. Expect increasing shower trends starting early next week as large scale stability decreases.

Discussion

The water vapor satellite imagery this evening shows fairly strong subsidence over the islands. Upper air balloon soundings from 2 PM HST (00Z) this afternoon show subsidence inversion temperature heights around 4,500 feet at Lihue limiting shower activity into the isolated range, with inversion heights near 7,000 feet at Hilo producing more scattered showers. A low pressure system roughly 1,300 miles northwest of Kauai will slowly drift closer to the islands over the weekend, weakening the ridge north of the state, and producing a slight decrease in trade winds speeds from Sunday to Monday.
Typical moderate to breezy trade wind weather will continue into the weekend with brief periods of showers for windward and mountain areas of most islands. The highest chances for showers in this weather regime will favor the overnight to early morning hours, with decreasing shower coverage during the daytime.
After a brief decrease in easterly trade wind speeds from Sunday to Monday, the subtropical ridge will build back north of the island chain. This stronger ridge will increase trade wind speeds back up to breezy levels from Tuesday to Wednesday. Shower trends will briefly increase, from Sunday night through Tuesday night, as large scale stability decreases. Remnant clouds from an old frontal band drift into the islands on the trade winds from Tuesday night to Wednesday morning.

Aviation

Breezy trades should keep the possibility of low cigs and SHRA along windward and mauka locations in the forecast. MVFR conds expected in SHRA otherwise VFR should prevail.
AIRMET Tango is in effect for mod turb below 070 for all islands and will likely be needed for a few days.

Marine

Fresh to strong easterly trades will persist through Saturday, then slightly ease over the western end of the state Sunday into Monday due to a weakness forming in the surface ridge as a front passes far to the north. The ridge will restrengthen Monday night through midweek as strong high pressure noses eastward behind the passing front. Despite the brief weakness Sunday into Monday, advisory levels winds may persist over the windier marine zones around Maui County and the Big Island, with an expansion to other waters Tuesday through midweek as the trades become strong over most waters.
Surf along south-facing will remain up around average through Tuesday as overlapping south swells move through. Expect the current south swell to hold through Saturday, then begin to lower Sunday. A fresh, long-period south-southwest pulse will arrive by Sunday night, peak Monday into Tuesday with surf climbing back to around average. A downward trend will follow late Tuesday through midweek.
Surf along east-facing shores will pick up slightly on Saturday, then remain steady around average through the upcoming week.
Surf along north-facing shores will gradually ease over the weekend as a medium-period north-northwest swell lowers. A background pulse arriving late Sunday into Monday may be enough to keep the surf from going flat. Surf may return to around average levels Tuesday through midweek as a medium-period north-northwest swell arrives.

HFO Watches/Warnings/Advisories

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

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