Hilo

Tonight: Mostly cloudy. Scattered showers until early morning, then scattered showers and chance of thunderstorms late in the night. Some thunderstorms may produce gusty winds late in the night. Locally heavy rainfall possible late in the night. Lows 61 to 69 near the shore to 50 to 57 at 4000 feet. Southwest winds up to 15 mph. Chance of rain 50 percent.

Thursday: Breezy. Mostly cloudy with scattered showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs 79 to 86 near the shore to 66 to 72 at 4000 feet. Southwest winds up to 25 mph with gusts to 45 mph. Chance of rain 50 percent.

Thursday Night: Breezy. Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows 62 to 70 near the shore to 52 to 60 at 4000 feet. Southwest winds up to 25 mph with gusts to 45 mph. Chance of rain 90 percent.

Kona

Tonight: Mostly cloudy. Scattered showers until early morning, then numerous showers and chance of thunderstorms late in the night. Some thunderstorms may produce gusty winds late in the night. Locally heavy rainfall possible late in the night. Lows around 71 near the shore to 45 to 51 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 60 percent.

Thursday: Breezy. Mostly cloudy with numerous showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs 81 to 88 near the shore to around 68 near 5000 feet. South winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Gusts up to 40 mph. Chance of rain 60 percent.

Thursday Night: Breezy. Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows 67 to 72 near the shore to 46 to 52 near 5000 feet. South winds up to 20 mph. Chance of rain 90 percent.

Waimea

Tonight: Mostly cloudy. Isolated showers until early morning, then chance of thunderstorms and isolated showers late in the night. Some thunderstorms may produce gusty winds late in the night. Locally heavy rainfall possible late in the night. Lows 61 to 69 near the shore to 53 to 60 near 3000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

Thursday: Mostly cloudy with scattered showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 80 near the shore to 71 to 78 near 3000 feet. West winds up to 15 mph. Gusts up to 35 mph in the afternoon. Chance of rain 50 percent.

Thursday Night: Breezy. Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows 62 to 70 near the shore to 54 to 62 near 3000 feet. Southwest winds up to 20 mph. Chance of rain 90 percent.

Kohala

Tonight: Mostly cloudy. Isolated showers until early morning, then chance of thunderstorms and isolated showers late in the night. Some thunderstorms may produce gusty winds late in the night. Locally heavy rainfall possible late in the night. Lows 61 to 69 near the shore to 53 to 60 near 3000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

Thursday: Mostly cloudy with scattered showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 80 near the shore to 71 to 78 near 3000 feet. West winds up to 15 mph. Gusts up to 35 mph in the afternoon. Chance of rain 50 percent.

Thursday Night: Breezy. Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows 62 to 70 near the shore to 54 to 62 near 3000 feet. Southwest winds up to 20 mph. Chance of rain 90 percent.

South Big Island

Tonight: Mostly cloudy. Scattered showers until early morning, then scattered showers and chance of thunderstorms late in the night. Some thunderstorms may produce gusty winds late in the night. Locally heavy rainfall possible late in the night. Lows around 71 near the shore to around 51 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Mostly cloudy with numerous showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 83 near the shore to around 67 near 5000 feet. East winds 10 to 15 mph. Chance of rain 60 percent.

Thursday Night: Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows around 71 near the shore to around 51 near 5000 feet. East winds up to 10 mph shifting to the southwest after midnight. Chance of rain 90 percent.

Puna

Tonight: Mostly cloudy. Scattered showers until early morning, then scattered showers and chance of thunderstorms late in the night. Some thunderstorms may produce gusty winds late in the night. Locally heavy rainfall possible late in the night. Lows 61 to 69 near the shore to 50 to 57 at 4000 feet. Southwest winds up to 15 mph. Chance of rain 50 percent.

Thursday: Breezy. Mostly cloudy with scattered showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs 79 to 86 near the shore to 66 to 72 at 4000 feet. Southwest winds up to 25 mph with gusts to 45 mph. Chance of rain 50 percent.

Thursday Night: Breezy. Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows 62 to 70 near the shore to 52 to 60 at 4000 feet. Southwest winds up to 25 mph with gusts to 45 mph. Chance of rain 90 percent.

Waikoloa

Tonight: Mostly cloudy. Numerous showers and chance of thunderstorms late in the night. Some thunderstorms may produce gusty winds late in the night. Locally heavy rainfall possible late in the night. Lows around 71 near the shore to 49 to 54 above 4000 feet. South winds up to 15 mph. Chance of rain 60 percent.

Thursday: Breezy. Mostly cloudy with numerous showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs 82 to 89 near the shore to 67 to 73 above 4000 feet. Southwest winds up to 25 mph with gusts to 45 mph. Chance of rain 60 percent.

Thursday Night: Breezy. Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows around 72 near the shore to 51 to 56 above 4000 feet. South winds up to 25 mph with gusts to 45 mph. Chance of rain 90 percent.

Detailed Forecast

Synopsis

Gentle to locally breezy south-southeast winds will continue to strengthen tonight into Thursday as a strong low approaches from the northwest. This strong winter low pressure system will pass just north of Kauai Thursday, with a cold front advancing down the island chain Thursday through Friday. The threat of flash flooding, damaging south to southwest winds, and strong to severe thunderstorms will precede the front. Conditions will quickly improve behind the front Friday night into the weekend, continuing through early next week.

Discussion

A gale low located roughly 820 miles northwest of Kauai this afternoon is producing a comma shaped cloud shield with the eastern edge of these high clouds thickening over the state. The low has also shifted east since this morning and local observations are showing winds have veered out of the southwest in the gentle to locally breezy range. Dewpoints have climbed from the 50s well into the 60's as the southerly air advects more moisture from the tropics. Radar imagery shows the scattered light to moderate showers early this morning have thinned out and are now just scattered light showers over portions of Oahu and Maui County streaming from the south to north. Southeast slopes of the Big Island has seen an increase clouds and isolated showers but rainfall totals remain modest due to inversion height around 5 kft.
Southerly flow is expected to strengthen tonight into Thursday generating potentially damaging downsloping winds mainly along northern and eastern slopes and coast, thus the High Wind Watch for Kauai, Oahu and Maui County has been upgraded to High Wind Warning starting tonight for Kauai and Oahu and Thursday morning for Maui County. The lower elevations of the Big Island remains in a high wind watch.
High resolution model guidance remains in good agreement and depicts shower activity increasing tonight within the southerly flow. A convective convergent band ahead of the main frontal boundary may develop near or over the central islands shortly after midnight tonight, thus grids have been updated to increase rainfall potential after midnight tonight for theses areas. The potential for thunderstorms will be greatest along this convergent band and ahead of the front tonight then expand state wide Thursday into Friday as the front and associated upper level support moves through the state. Additionally, deep convection will support the potential for periods of heavy snow over the Big Island Summits Thursday through Friday.
The strong surface low pressure will shift just north of Kauai Thursday before tracking northward and weakening Friday. Upper level support will also shift east of the state Friday into the weekend, drastically decreasing chances for strong winds, flash flooding and thunderstorms. Conditions will quickly improve Friday behind the front and through the weekend as high pressure builds in the wake of the front and attending low. Winds will Northerly winds will follow behind the front and veer northeasterly as the high develops north of the state. Dewpoints are expected to drop back into the upper 50's by the end of the weekend into early next week making for cooler and drier conditions. Moderate to breezy trades may return later in the weekend into early next week.

Aviation

A strong low pressure system will approach from the northwest this evening, then pass north of the islands tonight into Friday. A strong cold front will push down the island chain late tonight through Friday. Expect conditions to continue to deteriorate towards MVFR or lower over Kauai and Oahu this evening. Reduced flight conditions will spread across Maui County overnight and across the Big Island on Thursday. Strong southerly winds, heavy rain, and a few thunderstorms are possible through Thursday.
AIRMET Sierra for tempo mountain obscuration is in effect for Kauai and Oahu. This will likely be expanded to include Maui, Molokai, and Lanai tonight and possibly the Big Island on Thursday. AIRMET Sierra for IFR conditions is possible across the area Thursday.
AIRMET Zulu remains in effect for light in-cloud icing between FL200 and FL400, with conditions continuing through Thursday.
AIRMET Tango for strong surface winds will likely be issued tonight for Kauai and Oahu and on Thursday for Maui, Molokai, and Lanai. AIRMET Tango for mountain lee turbulence across north and east section will also be needed across the state through Thursday.

Marine

The center of a complex gale-force surface low will pass just N of the Hawaiian Offshore waters tonight through Thursday night, bringing the threats of strong to potentially severe thunderstorms, gale-force winds, and periods of very low visibility in heavy rain. Special Marine Warnings are likely during this time due to the high potential for strong thunderstorms producing gusts in excess of 34 kt. A Gale Warning is in effect for the waters around Kauai, and a Small Craft Advisory is posted elsewhere.
While most of the weather will occur in conjunction with strong and gusty S to SW winds, a cold front associated with the low will eventually move over the islands from Thursday night into Saturday, with moderate W to NW winds following the front, along with improving weather trends. Moderate to breezy NE trade winds will develop late in the weekend as high pressure develops far NW of the islands.
A fresh pulse of mid-period NNW swell has peaked well below High Surf Advisory (HSA) levels today. A larger N swell (generated by a gale-force low far N of the islands the last couple of days) will likely arrive Thursday night and Friday, pushing surf heights to HSA heights along N facing shores. The low passing N of the islands will continue to intensify as it moves away from the islands, likely delivering a larger N-NNE swell from Sunday into next week. A couple moderate-sized WNW swells are also expected, a smaller one this weekend, and a slightly larger one from Monday into Wednesday.
Rough and choppy surf (due to increasing short-period wind waves) will develop along S and W facing shores from tonight through Friday due to the increasingly strong low-level S-SW winds.

Fire weather

Critical fire weather conditions not expected through the forecast period.

HFO Watches/Warnings/Advisories

Flood Watch through Friday afternoon for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Haleakala Summit, Kona, Kohala, Big Island Interior, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island East, Big Island North.
High Wind Warning until 6 AM HST Friday for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward.
High Wind Warning from 6 AM Thursday to 6 AM HST Friday for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala.
High Wind Watch from Thursday morning through late Thursday night for Haleakala Summit, Kona, Kohala, Big Island Interior, Big Island South, Big Island Southeast, Big Island East, Big Island North.
High Wind Warning until 6 AM HST Friday for Big Island Summits.
Winter Storm Watch from Thursday morning through Friday morning for Big Island Summits.
Gale Warning until 6 AM HST Friday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel.
Small Craft Advisory until 6 AM HST Friday for Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov