Hilo

Rest Of Tonight: Windy. Mostly cloudy with numerous showers. Lows 62 to 71 near the shore to 53 to 61 at 4000 feet. Southwest winds up to 30 mph. Chance of rain 70 percent.

Friday: Windy. Mostly cloudy with numerous showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs 76 to 82 near the shore to 61 to 69 at 4000 feet. South winds up to 30 mph. Chance of rain 70 percent.

Friday Night: Mostly cloudy. Breezy. Numerous showers and chance of thunderstorms early in the evening, then scattered showers and chance of thunderstorms in the late evening and overnight. Some thunderstorms may produce gusty winds early in the evening. Locally heavy rainfall possible early in the evening. Lows 61 to 69 near the shore to 51 to 58 at 4000 feet. Southwest winds up to 20 mph. Chance of rain 70 percent.

Kona

Rest Of Tonight: Windy. Mostly cloudy with numerous showers and scattered thunderstorms. Some thunderstorms may produce gusty winds. Lows 69 to 74 near the shore to 48 to 54 near 5000 feet. South winds 10 to 30 mph. Chance of rain 70 percent.

Friday: Windy. Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs 80 to 85 near the shore to around 64 near 5000 feet. South winds 10 to 30 mph becoming southeast up to 20 mph in the afternoon. Chance of rain 90 percent.

Friday Night: Mostly cloudy. Breezy. Occasional showers and chance of thunderstorms early in the evening, then numerous showers and chance of thunderstorms in the late evening and overnight. Some thunderstorms may produce gusty winds early in the evening. Locally heavy rainfall possible early in the evening. Lows around 70 near the shore to 46 to 52 near 5000 feet. Southeast winds up to 20 mph shifting to the south up to 10 mph after midnight. Chance of rain 90 percent.

Waimea

Rest Of Tonight: Windy. Cloudy with scattered thunderstorms and isolated showers. Some thunderstorms may produce gusty winds. Lows 62 to 70 near the shore to 56 to 64 near 3000 feet. Southwest winds up to 35 mph. Chance of rain 50 percent.

Friday: Very windy. Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 77 near the shore to 67 to 74 near 3000 feet. West winds up to 30 mph shifting to the southwest up to 45 mph in the afternoon. Chance of rain 90 percent.

Friday Night: Mostly cloudy. Windy. Occasional showers and chance of thunderstorms early in the evening, then numerous showers and chance of thunderstorms in the late evening and overnight. Some thunderstorms may produce gusty winds early in the evening. Locally heavy rainfall possible early in the evening. Lows 61 to 69 near the shore to 54 to 62 near 3000 feet. South winds up to 30 mph shifting to the southwest up to 20 mph after midnight. Chance of rain 90 percent.

Kohala

Rest Of Tonight: Windy. Cloudy with scattered thunderstorms and isolated showers. Some thunderstorms may produce gusty winds. Lows 62 to 70 near the shore to 56 to 64 near 3000 feet. Southwest winds up to 35 mph. Chance of rain 50 percent.

Friday: Very windy. Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 77 near the shore to 67 to 74 near 3000 feet. West winds up to 30 mph shifting to the southwest up to 45 mph in the afternoon. Chance of rain 90 percent.

Friday Night: Mostly cloudy. Windy. Occasional showers and chance of thunderstorms early in the evening, then numerous showers and chance of thunderstorms in the late evening and overnight. Some thunderstorms may produce gusty winds early in the evening. Locally heavy rainfall possible early in the evening. Lows 61 to 69 near the shore to 54 to 62 near 3000 feet. South winds up to 30 mph shifting to the southwest up to 20 mph after midnight. Chance of rain 90 percent.

South Big Island

Rest Of Tonight: Cloudy with numerous showers and scattered thunderstorms. Some thunderstorms may produce gusty winds. Lows around 73 near the shore to around 54 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 70 percent.

Friday: Breezy. Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 81 near the shore to around 64 near 5000 feet. South winds 10 to 15 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 90 percent.

Friday Night: Mostly cloudy. Breezy. Occasional showers and chance of thunderstorms early in the evening, then numerous showers and chance of thunderstorms in the late evening and overnight. Some thunderstorms may produce gusty winds early in the evening. Locally heavy rainfall possible early in the evening. Lows around 72 near the shore to around 52 near 5000 feet. Northwest winds up to 25 mph shifting to the west up to 15 mph after midnight. Chance of rain 90 percent.

Puna

Rest Of Tonight: Windy. Mostly cloudy with numerous showers. Lows 62 to 71 near the shore to 53 to 61 at 4000 feet. Southwest winds up to 30 mph. Chance of rain 70 percent.

Friday: Windy. Mostly cloudy with numerous showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs 76 to 82 near the shore to 61 to 69 at 4000 feet. South winds up to 30 mph. Chance of rain 70 percent.

Friday Night: Mostly cloudy. Breezy. Numerous showers and chance of thunderstorms early in the evening, then scattered showers and chance of thunderstorms in the late evening and overnight. Some thunderstorms may produce gusty winds early in the evening. Locally heavy rainfall possible early in the evening. Lows 61 to 69 near the shore to 51 to 58 at 4000 feet. Southwest winds up to 20 mph. Chance of rain 70 percent.

Waikoloa

Rest Of Tonight: Very windy. Mostly cloudy with numerous showers and scattered thunderstorms. Some thunderstorms may produce gusty winds. Lows around 72 near the shore to 52 to 58 above 4000 feet. Southwest winds up to 40 mph becoming 10 to 35 mph after midnight. Chance of rain 70 percent.

Friday: Windy. Cloudy with occasional showers and chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs 80 to 85 near the shore to 62 to 68 above 4000 feet. South winds up to 35 mph. Chance of rain 90 percent.

Friday Night: Mostly cloudy. Windy. Occasional showers and chance of thunderstorms early in the evening, then numerous showers and chance of thunderstorms in the late evening and overnight. Some thunderstorms may produce gusty winds early in the evening. Locally heavy rainfall possible early in the evening. Lows around 72 near the shore to 50 to 55 above 4000 feet. South winds up to 30 mph shifting to the southwest up to 15 mph after midnight. Chance of rain 90 percent.

Detailed Forecast

Synopsis

Heavy showers and thunderstorms, a few of which may be severe, will shift from Oahu this evening to Maui County overnight into Friday. These storms will bring intense rain rates capable of producing flash flooding. Strong to severe winds southwest winds are also possible. Conditions will gradually improve with cooler and drier air building in behind the front Friday night through the weekend. Cool and breezy trade wind weather is expected through the first half of next week.

Discussion

The forecast area remains entrenched in the warm sector of a 986mb low positioned about 500 miles north of Kauai, or near 30N, at press time. Strong, deep layer southwesterlies persist this afternoon with gusts in excess of 50 mph measured on each island. Background warm advection is generally preventing higher end winds from mixing to the surface, as expected, but downsloping north and east of terrain in addition to convective forcing has nonetheless produced numerous strong wind gusts across the state many of which have been accompanied by downed trees and power lines. The nature of the wind threat will remain unchanged through tonight and the High Wind Watch looks to be in good shape through noon HST Friday.
A moderately unstable and strongly sheared airmass remains in place over Oahu and points east. The Severe Thunderstorm Watch will remain in effect until 6pm, mainly for thunderstorm wind gusts up to 60 mph. Model guidance has varied in their depictions of the convective evolution this afternoon into tonight. Generally speaking, warm sector convection has been too widespread in the global models and propagates eastward much too quickly in the high res guidance. Instead, convection remains anchored along the mid-level instability gradient, or the western edge of the unstable airmass which has resided over the island of Oahu for the balance of the day. Several waves of rainfall have already impacted the island with intense rain rates of 1-4″/hour observed. The latest GFS guidance indicates the mid-level/700mb instability gradient shifting east of Oahu into Maui County between roughly 6pm and midnight. During this time, convection should finally show a tendency to migrate eastward and will refocus heavy rain over Molokai, Lanai, and Maui (particularly leeward areas) for the remainder of the overnight period.
The high res guidance is once again hinting that heavy rain will shift east of Maui by Friday morning, but at this point this appears highly suspect as the instability gradient will reside over Maui for the entirety of the day on Friday. These solutions are treated with extreme caution, and suspect the flash flood threat for the island of Maui will continue well into Friday. The forecast for Maui is therefore unchanged for Friday and higher end pops remain in place. This outcome would likewise delay the onset of heavy rain over the Big Island (and snow over the summits). The instability gradient shifts over the Big Island late Friday into Friday night as low pressure pulls away and forcing diminishes potentially limiting any flash flood threat there. The forecast over the eastern end of the state remains largely unchanged at the moment but will be subject to revision as convective trends through tonight become more clear.
Finally, the cold front itself will reach Kauai tonight around midnight, falling apart as forcing weakens and dry air aloft spreads over existing frontal moisture. Flood potential will be limited by this time. Little will remain of the front once it reaches Oahu during the predawn hours Friday. This may allow the Flood Watch to expire early over the western portion of the state.
Pleasant, dry post-frontal airmass filters in over Kauai and Oahu for the weekend as trades return.

Aviation

An active weather pattern will continue across the state into Friday morning as a deep low pressure system passes to the north. A cold front approaches from the northwest, while a convergence band has set up over Oahu and Maui County late this afternoon producing intense thunderstorms/lightning, localized strong turbulence, reduced visibility and lowered ceilings, and mountain obscurations.
AIRMET Sierra is posted for IFR conditions over Oahu, Molokai and Maui entire island. AIRMET Sierra is also in effect for tempo mountain obscurations above 2000 feet for Kauai (also the entire island).
AIRMET Tango is posted for tempo moderate turbulence below 10,000 feet, and also from FL270 to FL400 (entire state). Strong sustained winds and downsloping gusts are expected along north and east sides of the islands, and AIRMET tango is posted for sustained winds of 30 knots or greater. Light icing is expected in layer 14,000 feet to FL240. These hazards will likely continue through Friday morning before the cold front slides past Kauai and quickly lifts northeastward.
The quickly evolving weather situation should be closely monitored for upates. Check for AIRMET and SIGMET updates on our website and on the Graphical Forecast for Aviation tool.

Marine

A strengthening 994mb low centered few hundred miles northwest of Kauai will continue to move eastward and pass north of the islands on Friday. Latest radar imagery is showing a line of strong to severe thunderstorms around Oahu this afternoon with damaging winds and waterspouts possible. The threat for strong to severe thunderstorms should gradually shift eastward tonight with Maui and Big Island waters expected to be impacted tonight into Friday. Special Marine Warnings have been ongoing over the coastal waters due to the strong thunderstorms producing gusts above 50 kt. A Gale Warning remains in effect for the waters around Kauai, and a Small Craft Advisory is posted for the remaining coastal waters. The Gale Warning should expire later tonight, but Small Craft Advisories will be likely for Friday.
Moderate to fresh W to NW winds with improving weather trends will quickly build in after the front passes through each island. The front should be pushing through the western half of the state on Friday and the eastern half of the state Friday night into Saturday. Moderate to locally strong NE trade winds will develop by Sunday as high pressure builds far NW of the islands.
Nearshore buoys are showing the new long-period N swell filling in this afternoon. This swell should peak this evening into tonight then slowly decline on Friday. The low passing N of the state continued to intensify during the day today with the daytime ASCAT pass showing a small fetch of 50 knots directed toward the state. This low will produce a wide range of swells with directions ranging anywhere from the SW to NNE through Saturday. The largest pulse will likely be with the fetch of 50 knot winds seen earlier today. This swell should fill in on Friday and could cause surf to reach advisory thresholds during the day Friday. A similar sized or slightly larger N to NNE swell is possible Sunday into early next week and surf may once again reach advisory thresholds. A couple moderate sized WNW swells are also expected, a smaller one this weekend, and a slightly larger one from Monday into Wednesday with the peak on Tuesday.
Rough and choppy surf along south and west facing shores, due to the strong to gale force kona winds will peak tonight and steadily decrease on Friday as the winds ease.

Fire weather

Critical fire conditions not expected during 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 noon HST Friday 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, 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 PM HST Friday for Haleakala Summit.
High Wind Warning until 6 AM HST Saturday for Big Island Summits.
Winter Storm Warning until 6 AM HST Saturday 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