Hilo

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 57 to 65 near the shore to 47 to 54 at 4000 feet. Northwest winds up to 10 mph in the evening becoming light. Chance of rain 60 percent.

Wednesday: Mostly cloudy. Breezy. Scattered showers in the morning, then isolated showers and thunderstorms in the afternoon. Highs 75 to 82 near the shore to 62 to 69 at 4000 feet. South winds up to 20 mph. Chance of rain 50 percent.

Wednesday Night: Breezy. Mostly cloudy with scattered showers. Lows 61 to 69 near the shore to 50 to 57 at 4000 feet. South winds up to 25 mph. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy with isolated showers. Lows around 69 near the shore to 43 to 49 near 5000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs around 83 near the shore to around 67 near 5000 feet. Southeast winds up to 10 mph shifting to the southwest in the afternoon. Gusts up to 30 mph. Chance of rain 20 percent.

Wednesday Night: Breezy. Mostly cloudy with scattered showers. Lows around 71 near the shore to 45 to 51 near 5000 feet. Southwest winds up to 20 mph shifting to the southeast after midnight. Chance of rain 30 percent.

Waimea

Tonight: Mostly cloudy with scattered showers. Lows 58 to 67 near the shore to 51 to 58 near 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Wednesday: Mostly cloudy with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 77 near the shore to 67 to 75 near 3000 feet. East winds up to 10 mph shifting to the north in the afternoon. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 61 to 69 near the shore to 53 to 60 near 3000 feet. Northwest winds up to 15 mph shifting to the south after midnight. Chance of rain 30 percent.

Kohala

Tonight: Mostly cloudy with scattered showers. Lows 58 to 67 near the shore to 51 to 58 near 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Wednesday: Mostly cloudy with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 77 near the shore to 67 to 75 near 3000 feet. East winds up to 10 mph shifting to the north in the afternoon. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 61 to 69 near the shore to 53 to 60 near 3000 feet. Northwest winds up to 15 mph shifting to the south after midnight. Chance of rain 30 percent.

South Big Island

Tonight: Mostly cloudy with isolated showers. Lows around 70 near the shore to around 49 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Breezy. Partly sunny with isolated showers in the morning, then mostly sunny in the afternoon. Highs around 82 near the shore to around 67 near 5000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

Wednesday Night: Breezy. Mostly cloudy with scattered showers and isolated thunderstorms. Lows around 71 near the shore to around 51 near 5000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

Puna

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 57 to 65 near the shore to 47 to 54 at 4000 feet. Northwest winds up to 10 mph in the evening becoming light. Chance of rain 60 percent.

Wednesday: Mostly cloudy. Breezy. Scattered showers in the morning, then isolated showers and thunderstorms in the afternoon. Highs 75 to 82 near the shore to 62 to 69 at 4000 feet. South winds up to 20 mph. Chance of rain 50 percent.

Wednesday Night: Breezy. Mostly cloudy with scattered showers. Lows 61 to 69 near the shore to 50 to 57 at 4000 feet. South winds up to 25 mph. Chance of rain 50 percent.

Waikoloa

Tonight: Mostly cloudy. Isolated showers after midnight. Lows around 69 near the shore to 46 to 52 above 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Partly sunny in the morning then becoming mostly sunny. Highs 80 to 86 near the shore to 64 to 69 above 4000 feet. East winds up to 10 mph shifting to the northwest in the afternoon.

Wednesday Night: Breezy. Mostly cloudy with scattered showers. Lows around 71 near the shore to 49 to 54 above 4000 feet. Northwest winds up to 20 mph shifting to the south after midnight. Gusts up to 45 mph. Chance of rain 30 percent.

Detailed Forecast

Synopsis

Cool and breezy northerly winds will weaken tonight and become southerly on Wednesday. A strong winter low pressure system will develop west of the islands Wednesday night and pass by just north of Kauai on Thursday, with the associated cold front moving eastward across the state Thursday into Friday. This system will bring the threat of flash flooding, damaging south to southwest winds, and strong to severe thunderstorms Wednesday night through Friday. Much cooler and drier weather will move in behind the front Friday night and Saturday and continue through early next week.

Discussion

Breezy northerly winds will continue to weaken overnight as a ridge of high pressure builds to the north of the state. Satellite imagery this afternoon shows extensive low clouds over windward and mauka areas of most islands, with limited shower activity. Guidance continues to show the front east of the Big Island dissipating tonight with some frontal remnants lifting northward on Wednesday. Increasing south to southeasterly flow will bring a gradual increase in showers Wednesday, with the focus shifting to south and southeast facing slopes and coasts.
The main forecast concerns continue to revolve around the development of a storm system that is currently around 900 miles west-northwest of Kauai. This system will bring a multi-faceted threat for significant weather to the Hawaiian Islands starting Wednesday night and continuing through Friday morning. As such, the following weather headlines have been issued…
– A Flood Watch for the entire state, – A High Wind Watch for the entire state, including the summits of Haleakala, Mauna Kea, and Mauna Loa, and – A Winter Storm Watch for the summits of Haleakala, Mauna Kea, and Mauna Loa.
Guidance continues to show a strong winter low developing several hundred miles northwest of Kauai on Wednesday night. The low will shift eastward and pass by a couple hundred miles north of Kauai on Thursday, then drag a cold front eastward across the state Thursday night and Friday. In advance of the low and associated cold front, dewpoints will climb into the lower 70s, 0-1 km MUCAPE values rise to 1500-2000 J/KG, 0-6 KM Bulk Shear values hover in the 35-45 kt range. This will potentially bring strong to severe thunderstorms with a threat for strong winds. Rainfall totals with this system range from 4 to 7 inches across the state. Stay tuned for further updates as the event draws closer and timing details become more clear.
Much drier and cooler weather will move in behind the front Friday night and Saturday, and continue through early next week.

Aviation

Moderate N-NE winds will weaken and veer to the E overnight, and become SE Wednesday as low pressure develops NW of the islands. Low clouds and showers will favor windward areas, with periods of MVFR CIG/VIS in SHRA likely, especially over windward Big Island, where AIRMET Sierra is posted for mountain obscuration. VFR conditions will continue to prevail over Kauai and Oahu overnight.

Marine

A ridge of high pressure building just north of the state will bring a decrease of our winds tonight with gentle to moderate east winds expected tonight. Winds are expected to gradually strengthen on Wednesday and veer southeasterly as a powerful low pressure system approaches. This low will begin to approach the western offshore waters on Wednesday, where a Gale Warning is expected. The strongest winds are expected over the NW half of the offshore waters.
From Wednesday night through Friday, a strong low pressure passing near the state will bring the threat of severe thunderstorms, gale force winds, and heavy rain across the state. Winds will primarily be strong to gale force out of the southwest through Thursday with damaging wind gusts possible with any thunderstorms. As the associated cold front pushes through Friday, westerly winds will follow with improving weather conditions. Marine Weather Warnings are likely during this time due to the high potential for strong thunderstorms. A Gale Watch is also in effect for the waters around Kauai Wednesday night through Thursday.
A new north-northwest swell will continue to fill in tonight and should peak late tonight into Wednesday morning below advisory thresholds. A larger north swell should fill in later Thursday into Friday, which could reach advisory levels for north facing shores. Several reinforcing pulses are expected Friday into early next week as the swell veers more northeasterly and could produce advisory level surf along east facing shores due to the shift in swell direction this weekend. A moderate west-northwest swell will eventually move in with the overlapping north to northeast swells on Monday and peak on Tuesday.
Surf along south-facing shores will remain small into Wednesday. Rough and choppy surf will develop along south and west facing shores from Wednesday night through Friday due to the strong kona winds developing from the aforementioned low pressure system.

Fire weather

Critical fire weather conditions not expected through the forecast period.

HFO Watches/Warnings/Advisories

Flood Watch from Wednesday evening through Friday morning for all Hawaii islands,
High Wind Watch from Wednesday evening through late Thursday night for all Hawaii islands,
Winter Storm Watch from late Wednesday night through late Thursday night for Haleakala Summit.
Winter Storm Watch from late Wednesday night through Friday morning for Big Island Summits.
Gale Watch from Wednesday evening through Thursday afternoon for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel.

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Data Courtesy of NOAA.gov