West Kaua’i

Tonight: Partly cloudy. Isolated showers after midnight. Lows around 72 near the shore to around 61 above 3000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 20 percent.

Saturday: Sunny with isolated showers. Highs 85 to 90 near the shore to around 74 above 3000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Saturday Night: Mostly clear. Isolated showers after midnight. Lows around 72 near the shore to around 61 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 72. East winds around 15 mph. Chance of rain 40 percent.

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

Saturday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 72. East winds around 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 66 to 71 in the valleys to around 59 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 73 to 86 in the valleys to 62 to 67 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Saturday Night: Breezy. Mostly cloudy with scattered showers. Lows 66 to 71 in the valleys to around 59 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 65 to 74. East winds 10 to 15 mph. Chance of rain 40 percent.

Saturday: Mostly sunny with scattered showers. Highs 78 to 87. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday 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: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 65 to 76. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs 73 to 85. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday 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 will become breezy and gusty Saturday through at least Tuesday as strong high pressure develops far north of the state. 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

Somewhat typical early July conditions prevail across the state, though slightly wetter on Oahu and Maui County. Broad surface high pressure far north of the islands continues to drive moderate to locally breezy trade winds, and a building ridge aloft has pushed the inversion down to 6,000 to 6,500 ft. A shallow and diffuse band of moisture moving within this stable trade wind flow has kept conditions somewhat cloudy on Oahu and Maui County, where up to a quarter of an inch of rainfall was measured on windward slopes today, and a narrow band of high clouds has also been focused over the central portion of the island chain. Rainfall and cloud cover has been less extensive on Kauai and Big Island, though some afternoon showers are expected along the South Kona slopes. No big changes are due tonight, with rain chances diminishing on leeward Big Island.
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 continue to build overhead and push the inversion to as low as 5,000 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. Guidance shows no distinct organized areas of moisture as precipitable water stays 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

Breezy easterly trade winds will become gusty this weekend as high pressure strengthens far northeast of the state. A fairly stable environment will keep only brief passing showers in the forecast, favoring windward and mountain areas. VFR flight conditions will prevail for most locations, though brief MVFR ceilings and visibilities will be possible within any showers that pass through.
AIRMET Tango remains in effect for moderate low-level turbulence over and downwind of island terrain. This AIRMET will likely persist into early next week as gusty trades continue.

Marine

High pressure north of the islands will continue to strengthen over the weekend and linger into next week. Strong trade winds will develop by Saturday and continue through the beginning of next week. The current Small Craft Advisory remains in effect for most waters through Sunday afternoon. This will likely get extended into next week and could get expanded to cover the remaining waters. The high will weaken slightly by the middle of next week causing trades to marginally decrease into the breezy to locally strong range for the latter half of the week.
Surf for south facing shores will gradually fall below the summertime average over the weekend as the current S swell subsides. Tiny, long-period S swells will then hold into next week until a new small, long-period swell fills in by Tuesday night. This new swell could boost surf heights near the summertime average (5 ft) by the middle of next week.
Surf for east facing shores will increase this weekend and become rough and choppy as trade wind speeds increase. Surf along north and west facing showers will remain small.

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 to around 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 at times, 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 Kauai Northwest Waters, Kauai Leeward Waters, Kauai Channel, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Kauai Now Weather is brought to you by Blue Hawaiian Helicopters.