Hilo

Tonight: Cloudy and breezy. Showers and slight chance of thunderstorms early in the evening, then slight chance of thunderstorms and isolated showers in the late evening and overnight. Locally heavy rainfall possible. Lows 62 to 70 near the shore to 53 to 59 at 4000 feet. South winds up to 25 mph. Chance of rain 80 percent.

Thursday: Breezy. Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 80 near the shore to around 66 at 4000 feet. South winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Gusts up to 55 mph. Chance of rain 80 percent.

Thursday Night: Breezy. Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 62 to 70 near the shore to 53 to 59 at 4000 feet. South winds up to 20 mph. Gusts up to 45 mph decreasing to 35 mph after midnight. Chance of rain 90 percent.

Kona

Tonight: Windy. Cloudy with slight chance of thunderstorms and isolated showers. Locally heavy rainfall possible. Lows around 72 near the shore to 51 to 56 near 5000 feet. Northwest winds up to 15 mph shifting to the south up to 30 mph with gusts to 60 mph after midnight. Chance of rain 20 percent.

Thursday: Windy. Cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 85 near the shore to around 67 near 5000 feet. Northeast winds up to 35 mph shifting to the southeast in the afternoon. Gusts up to 65 mph. Chance of rain 70 percent.

Thursday Night: Windy. Cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 72 near the shore to 51 to 56 near 5000 feet. East winds up to 30 mph. Gusts up to 60 mph decreasing to 45 mph after midnight. Chance of rain 70 percent.

Waimea

Tonight: Cloudy with slight chance of thunderstorms and isolated showers. Locally heavy rainfall possible. Lows 63 to 71 near the shore to 56 to 63 near 3000 feet. Light winds. Chance of rain 20 percent.

Thursday: Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 81 near the shore to 70 to 77 near 3000 feet. West winds up to 10 mph. Chance of rain 80 percent.

Thursday Night: Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 63 to 70 near the shore to 56 to 63 near 3000 feet. North winds up to 10 mph. Chance of rain 80 percent.

Kohala

Tonight: Cloudy with slight chance of thunderstorms and isolated showers. Locally heavy rainfall possible. Lows 63 to 71 near the shore to 56 to 63 near 3000 feet. Light winds. Chance of rain 20 percent.

Thursday: Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 81 near the shore to 70 to 77 near 3000 feet. West winds up to 10 mph. Chance of rain 80 percent.

Thursday Night: Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 63 to 70 near the shore to 56 to 63 near 3000 feet. North winds up to 10 mph. Chance of rain 80 percent.

South Big Island

Tonight: Cloudy and windy. Showers likely and slight chance of thunderstorms early in the evening, then scattered showers and slight chance of thunderstorms in the late evening and overnight. Locally heavy rainfall possible. Lows around 73 near the shore to around 56 near 5000 feet. East winds 15 to 30 mph. Gusts up to 50 mph after midnight. Chance of rain 70 percent.

Thursday: Windy. Cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 83 near the shore to around 64 near 5000 feet. East winds 15 to 35 mph with gusts to 55 mph. Chance of rain 70 percent.

Thursday Night: Cloudy and windy. Showers likely and slight chance of thunderstorms until early morning, then frequent showers and slight chance of thunderstorms early in the morning. Locally heavy rainfall possible. Lows around 73 near the shore to around 55 near 5000 feet. Northeast winds 15 to 30 mph. Chance of rain 80 percent.

Puna

Tonight: Cloudy and breezy. Showers and slight chance of thunderstorms early in the evening, then slight chance of thunderstorms and isolated showers in the late evening and overnight. Locally heavy rainfall possible. Lows 62 to 70 near the shore to 53 to 59 at 4000 feet. South winds up to 25 mph. Chance of rain 80 percent.

Thursday: Breezy. Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 80 near the shore to around 66 at 4000 feet. South winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Gusts up to 55 mph. Chance of rain 80 percent.

Thursday Night: Breezy. Cloudy with showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 62 to 70 near the shore to 53 to 59 at 4000 feet. South winds up to 20 mph. Gusts up to 45 mph decreasing to 35 mph after midnight. Chance of rain 90 percent.

Waikoloa

Tonight: Cloudy with slight chance of thunderstorms and isolated showers. Locally heavy rainfall possible. Lows around 73 near the shore to 53 to 58 above 4000 feet. Light winds. Chance of rain 20 percent.

Thursday: Cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 83 near the shore to 65 to 70 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Thursday Night: Cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 72 near the shore to 54 to 59 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

An increasingly active weather pattern unfolding across the Hawaiian Islands will persist through Friday as low pressure strengthens northwest of the state. Deep tropical moisture being drawn northward into the islands will support periods of heavy rainfall, strong southerly winds, isolated strong to severe thunderstorms, particularly from Thursday through Friday. Although some brief improvement for portions of the state is possible by Saturday, another active period appears likely from Sunday through early next week.

Discussion

Forecast confidence continues to increase in a high-impact weather event evolving across the state from late tonight through Friday, with the primary concerns being heavy rainfall, strong southerly winds, and strong to severe thunderstorms.
Model guidance remains in good agreement depicting a deep upper trough and embedded shortwave energy digging southeastward toward the islands while surface low pressure deepens northwest of the state. As this system strengthens, the local pressure gradient will continue to tighten through Thursday, resulting in increasingly strong south to southeast winds across the island chain.
This flow will continue to transport a deep tropical moisture plume northward over the state, with PWs expected to hover around or above 2 inches. Combined with increasing large-scale ascent and strengthening low-level convergence, conditions continue to favor widespread and organized heavy rainfall and isolated strong to severe thunderstorms (despite the best instability remaining off to the northwest).
The greatest rainfall impacts still appear most likely to begin over Kauai and Oahu late tonight and into Thursday before spreading eastward across the remainder of the state Thursday night through Friday. Confidence remains highest across the western end of the island chain for the most significant rainfall totals and flash flooding concerns during the initial phase of the event.
Wind impacts are also becoming increasingly concerning. Guidance supports strong and gusty southerly winds across Kauai and Oahu Thursday through Thursday night, and an upgrade from the current High Wind Watch to a High Wind Warning appears likely with the overnight forecast cycle.
Farther east, guidance also indicates gusty southerly winds across exposed portions of the Big Island during the same time period. While winds there are not currently expected to reach warning criteria, speeds may become strong enough to warrant a Wind Advisory, particularly across wind-prone and terrain-enhanced areas by late Thursday or Friday.
Although forecast confidence decreases somewhat beyond Friday, some gradual or temporary improvement is anticipated Friday night into Saturday as upper heights rise and some drier air advances down the island chain from the west. Guidance, however, shows another shortwave dipping southeastward into the area late in the weekend, likely supporting another active weather period across the state that may extend through early next week.

Aviation

Showers are expected to envelop the islands for most of the night. Conditions will vary depending on shower intensity as a result, but expect at least borderline MVFR conditions for most sites through at least early morning Thursday. Weather models suggest a brief break in the rain for at least the eastern half of the state around daybreak Thursday, before rain recommences by Thursday afternoon and evening. Winds will ramp up across most sites by Thursday afternoon as well, mainly out of the south.
AIRMET Sierra is in effect for mountain obscuration above 020 ft across all islands. Some relief is possible as showers decrease in coverage, but confidence in exact timing is low, so expect Sierra to persist through the TAF period.
AIRMET Tango is also in effect for moderate turbulence between FL200 and FL350 across the entire islands. This is also expected to remain in effect through the TAF period.

Marine

South to southeast winds are expected to steadily increase through Thursday night, as a low pressure system develops just west of the state. A Small Craft Advisory (SCA) remains in effect for portions of the coastal waters tonight and will expand in coverage on Thursday. A Gale Watch remains in effect for Thursday into Thursday night across the Hawaiian Waters. At this time, it is looking like the strongest winds will start off over the western half of the state Thursday into Thursday night and expand towards the eastern half of the state Thursday night into Friday.
As the low pressure system further deepens Thursday into Friday, we will likely see a greater coverage of thunderstorms and gusty winds. Very rough boating conditions are expected late Thursday into Friday as seas quickly rise in response to the strong to gale force winds. South facing harbor entrances will also be greatly impacted due to rough conditions.
The current south swell that peaked during the day today will slowly drop tonight through the rest of the week. A High Surf Advisory is in effect for all south facing shores of the Hawaiian Islands through 6 AM.
As the long-period south swell declines on Thursday, strong to gale force southerly winds are expected to develop and strengthen even further Thursday night into Friday. This increase of southerly winds will bring a rapid increase of short-period energy Thursday into Friday and will once again bring surf heights above the advisory thresholds for south facing shores. Large disorganized surf is expected along many south facing shores Thursday into Friday.
Along north facing shores, a moderate long-period northwest (310-320 degree) swell peaked during the day today and will steadily lower Thursday into Friday. However a smaller short- period northwest swell generated by the low developing just west of us at the moment will fill in over the weekend into early next week.
Surf along east facing shores could see an increase later this week due to the strengthening southeasterly winds especially for southeast exposures.

HFO Watches/Warnings/Advisories

Flood Watch through Friday afternoon for all Hawaii islands,
High Surf Advisory until 6 AM HST Thursday for Niihau, Kauai Leeward, Waianae Coast, Kahoolawe, Maui Leeward West, Kona, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Molokai West, Molokai Leeward South, Lanai Leeward, Lanai South, Maui Central Valley South, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast.
High Wind Watch from 6 AM HST Thursday through late Thursday night for Kauai Mountains, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Kauai North, Koolau Windward, Koolau Leeward.
Winter Weather Advisory until 6 AM HST Friday for Big Island Summits.
Wind Advisory from 2 PM Thursday to 6 PM HST Friday for Big Island Summits.
Small Craft Advisory until 6 AM HST Thursday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Leeward Waters, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.
Gale Watch from 6 AM HST Thursday through late Thursday night for all Hawaiian waters,

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Data Courtesy of NOAA.gov