West Kaua’i

Tonight: Mostly cloudy in the evening, then partly cloudy with isolated showers after midnight. Lows around 72 near the shore to around 62 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Independence Day: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 84 to 90 near the shore to around 77 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Friday Night: Mostly clear. Isolated showers after midnight. Lows 69 to 74 near the shore to around 62 above 3000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 73. East winds 10 to 15 mph. Chance of rain 40 percent.

Independence Day: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 73. East winds around 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 70 in the valleys to around 59 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Independence Day: Mostly cloudy. Breezy. Occasional showers in the morning, then scattered showers in the afternoon. Highs 74 to 84 in the valleys to around 66 above 4000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 64 to 69 in the valleys to around 59 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 66 to 74. East winds up to 15 mph. Chance of rain 40 percent.

Independence Day: Partly sunny with numerous showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 77 to 87. East winds up to 15 mph. Chance of rain 70 percent.

Friday Night: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 65 to 73. East winds 10 to 15 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 65 to 76. East winds 10 to 15 mph. Chance of rain 50 percent.

Independence Day: Mostly cloudy with numerous showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 72 to 85. East winds 10 to 15 mph. Chance of rain 70 percent.

Friday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 65 to 76. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Stable trade winds will increase late Friday and will be breezy and gusty Saturday through at least Tuesday. Modest showers will be focused along windward slopes, and aside from afternoon showers over the Kona slopes of the Big Island, leeward areas will be mostly dry.

Discussion

Typical early summer conditions are in place. Broad surface high pressure north of the state is driving moderate to locally breezy trade winds, and mid level ridging is producing an inversion based between 6,500 and 7,500 feet. Precipitable water is running near to just below seasonal normal, and little organized moisture is observed in the trade wind flow. As a result, rainfall has been modest and focused over windward slopes, where less than a half of an inch has been measured during the past 24 hours, and most leeward areas have been dry. The only exceptions are the Kona slopes of the Big Island and portions of Upcountry Maui, where spotty afternoon showers will taper off later in the evening. Little change is expected into Independence Day.
Trade winds will become breezy on Saturday, and the stable, gusty and rather dry conditions will persist through at least Tuesday. Trades will increase as surface high pressure far northeast of Hawaii strengthens to around 1032 mb. A mid level ridge will build overhead and push the inversion down to 5,000 to 6,500 feet. The interaction of the breezy trade wind flow with the islands should generate wind gusts around 40 mph over and downwind of terrain, though isolated areas on the Big Island and Maui County could approach Wind Advisory criteria at times. The GFS and ECMWF are showing no distinct organized areas of moisture with precipitable water below seasonal average. This should result in modest windward rainfall and aside from scattered afternoon and evening showers on the Kona slopes of the Big Island, dry leeward conditions. See the Fire Weather section below for additional discussion. A slight decrease in trade winds is expected Wednesday.

Aviation

Moderate to locally breezy trade winds will prevail across the island chain for the next several days. Low clouds and showers will focus mainly along windward and mountain areas, though some isolated showers could spill over into leeward areas from time to time. MVFR ceilings and visibilities will be possible within any passing showers, but VFR flight conditions will generally prevail at most locations throughout the next few days.
AIRMET Tango has been issued today for moderate low-level turbulence over and downwind of island terrain. This AIRMET will likely persist into the weekend as breezy trades continue.

Marine

High pressure restrengthens and establishes north of the islands causing strong trades to develop this weekend. The existing Small Craft Advisory has been extended through the weekend and will require further expansion in areal coverage next week.
Existing S swell declines through the weekend causing surf to fall below the summertime average. Tiny, long period S swell then holds into next week as below average surf continues. Wind waves and short period fresh swell will become more prominent as trades strengthen this weekend into next week. N shore remains tiny.

Fire weather

Breezy, gusty, and rather dry conditions will develop on Saturday and persist into early next week. Relative humidity at lower leeward elevations will likely fall below 45 percent each afternoon, and with the inversion dropping to as low as 5,000 feet winds will become gusty over and downwind of terrain. This will result in near critical fire weather conditions over dry leeward areas, though no headlines (watches or warnings) are due since the Keetch Byram Drought Index will remain below the 600 threshold at Honolulu.

HFO Watches/Warnings/Advisories

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

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