West Kaua’i

Tonight: Partly cloudy. Breezy. Lows 69 to 76 near the shore to around 63 above 3000 feet. Northeast winds up to 20 mph.

Thursday: Mostly sunny. Isolated showers in the morning. Highs 86 to 91 near the shore to around 78 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Thursday Night: Partly cloudy. Isolated showers after midnight. Lows 70 to 75 near the shore to around 63 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 74. Northeast winds 15 to 20 mph. Chance of rain 40 percent.

Thursday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 82 to 90. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows 71 to 76. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 68 in the valleys to around 60 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Thursday: Breezy. Partly sunny with scattered showers. Highs 75 to 84 in the valleys to around 67 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows 65 to 71 in the valleys to around 59 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 66 to 75. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Breezy. Partly sunny with scattered showers. Highs 78 to 88. East winds 10 to 20 mph. Chance of rain 50 percent.

Thursday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 66 to 74. East winds around 10 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 76. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Thursday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 75 to 87. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows 65 to 77. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A high pressure ridge will remain in place north of the Hawaiian Islands into the first half of next week. Expect moderate to breezy trade winds through Thursday. Winds will ease slightly to more moderate speeds Friday through Sunday. Expect showers to focus mainly along windward and mauka slopes especially overnight and early morning. An increase in shower activity and instability is expected as early as late Thursday into Saturday as an upper level low develops northwest of the state. Typical summertime, stable trade wind weather is expected to gradually return Sunday onward as an upper level ridge builds over the region.

Discussion

A surface ridge north of the Hawaiian Islands is producing moderate to locally breezy trade winds. Afternoon satellite and radar imagery show showers have trended down since this morning. Clouds and isolated showers are favoring windward and mauka ranges with a few clouds and showers developing along the Kona slopes this afternoon. Chances of showers will increase tonight along windward and mauka areas due typical diurnal trade wind pattern and as pockets of moisture move from east to west within the tradewind flow and a clouds and showers clearing along Kona slopes as land breezes develop. Similar day time conditions experienced today is expected during the day Thursday.
Forecast remains on track, with chances of clouds and showers increasing late Thursday as an area of near to slightly above normal moisture moves east to west as a weak upper level low develops northwest of Kauai. This combination of upper level and low level moisture will lift the temperature inversion heights to around the 7,000 foot range, increasing rainfall activity into the scattered to numerous range, mainly over windward and mountain areas in the overnight to early morning hours with a few showers making it to leeward areas of the small islands. There is also a non-zero chance of isolated thunderstorms developing north and west of Kauai. The EC model guidance is showing a more robust signature than the GFS which is not generating enough confidence put in the forecast at the moment. Expected rainfall totals during the Friday and Saturday time period, are expected to remain between 0.10 inch to 0.50 inch where the higher amounts expected in and around terrain favored locations.
Stable summertime trade wind pattern is expected to gradually return Sunday. A drier airmass is expected to filter in first for the eastern half of the state as the upper level level shifts northeast of the state. The upper level low is expected to weaken into a trough and exit northeast of the state by early next week and the lingering moisture plume should push north and west allowing for drier and more stable conditions develop state wide.

Aviation

A locally breezy and rather stable trade wind flow will persist through Thursday. Periods of MVFR ceilings and visibility in SHRA will be confined to windward areas of all islands, as well as the South Kona slopes of the Big Island during the afternoon and evening hours. AIRMET Tango for low level turbulence will remain in effect below 7,000 ft over and downwind of terrain.
Trade winds will ease slightly Friday and Saturday, and shower activity may increase as the atmosphere becomes less stable.

Marine

High pressure will remain far northeast of the state through the rest of the week. Fresh to locally strong trades will persist through Thursday, then wind speeds may drop slightly as a weak low level trough develops in the easterly flow and moves across the state Thursday night into the weekend. A Small Craft Advisory (SCA) remains in effect for the typical windy areas around Maui County and the Big Island through Thursday.
A fading medium period south swell combined with a fading south- southeast swell will maintain below summer average surf on the south facing shores through tomorrow. A slight bump in surf is expected this weekend as a new long-period southwest swell arrives from the Tasman Sea, along with a new small short-period south- southeast swell. The Tasman swell is expected to peak on Saturday, with surf heights topping near the summer average before gradually declining into early next week.
Surf along east facing shores will continue to remain rough and choppy due to the fresh to locally strong trade winds and a small short-period northeast swell that is expected to fill in this weekend. Surf along north facing shores will remain nearly flat through the weekend.
Minor coastal flooding along the shoreline and in low-lying coastal areas will be possible around the daily high tide starting Monday of next week due to peak monthly tides and higher than predicted water levels at select locations.

Fire weather

Trade winds will remain in the moderate to locally breezy range through Thursday before weakening slightly into the weekend. Shower trends are expected to increase as early as Thursday night through Friday and hold into Saturday night. A weak upper level disturbance will near northwest Kauai late Thursday and Friday, increasing instability slightly. At the same time a area of low level moisture will move from east to west across the state, increasing chances of showers mainly for windward a mauka areas but could also spill over to leeward areas of the smaller islands at times as the temperature inversion heights increase. Drier and more stable weather is expected to gradually return from east to west Sunday into early next week. Borderline fire weather concerns over leeward areas may be of concern middle of next week as breezy, dry and stable trade wind pattern develops.

HFO Watches/Warnings/Advisories

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

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