Hilo

Tonight: Mostly clear. Isolated showers in the evening. Lows 60 to 69 near the shore to 51 to 56 at 4000 feet. Southwest winds up to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Highs 80 to 85 near the shore to 65 to 72 at 4000 feet. South winds up to 15 mph. Chance of rain 20 percent.

Thursday Night: Mostly clear. Isolated showers in the evening. Lows 61 to 69 near the shore to 50 to 56 at 4000 feet. Light winds. Chance of rain 20 percent.

Kona

Tonight: Mostly clear. Lows 68 to 74 near the shore to 46 to 52 near 5000 feet. East winds up to 10 mph.

Thursday: Sunny. Isolated showers in the afternoon. Highs 82 to 88 near the shore to around 68 near 5000 feet. Southwest winds up to 15 mph. Chance of rain 20 percent.

Thursday Night: Mostly clear. Lows 69 to 74 near the shore to 47 to 52 near 5000 feet. Light winds.

Waimea

Tonight: Partly cloudy. Isolated showers in the evening. Lows 61 to 70 near the shore to 53 to 61 near 3000 feet. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 79 near the shore to 69 to 77 near 3000 feet. Light winds. Chance of rain 50 percent.

Thursday Night: Partly cloudy. Scattered showers in the evening. Lows 61 to 70 near the shore to 54 to 62 near 3000 feet. Light winds. Chance of rain 40 percent.

Kohala

Tonight: Partly cloudy. Isolated showers in the evening. Lows 61 to 70 near the shore to 53 to 61 near 3000 feet. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 79 near the shore to 69 to 77 near 3000 feet. Light winds. Chance of rain 50 percent.

Thursday Night: Partly cloudy. Scattered showers in the evening. Lows 61 to 70 near the shore to 54 to 62 near 3000 feet. Light winds. Chance of rain 40 percent.

South Big Island

Tonight: Mostly clear with isolated showers. Lows around 73 near the shore to around 53 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 85 near the shore to around 68 near 5000 feet. East winds 10 to 15 mph. Chance of rain 30 percent.

Thursday Night: Mostly clear. Lows around 73 near the shore to around 54 near 5000 feet. East winds around 10 mph.

Puna

Tonight: Mostly clear. Isolated showers in the evening. Lows 60 to 69 near the shore to 51 to 56 at 4000 feet. Southwest winds up to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Highs 80 to 85 near the shore to 65 to 72 at 4000 feet. South winds up to 15 mph. Chance of rain 20 percent.

Thursday Night: Mostly clear. Isolated showers in the evening. Lows 61 to 69 near the shore to 50 to 56 at 4000 feet. Light winds. Chance of rain 20 percent.

Waikoloa

Tonight: Mostly clear. Lows 69 to 74 near the shore to 48 to 54 above 4000 feet. Light winds becoming southeast up to 10 mph after midnight.

Thursday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 82 to 87 near the shore to 65 to 71 above 4000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Thursday Night: Partly cloudy. Scattered showers in the evening. Lows 69 to 74 near the shore to 49 to 54 above 4000 feet. Light winds. Chance of rain 30 percent.

Detailed Forecast

Synopsis

A stalled cold front near Kauai will produce periods of moderate to locally heavy showers and a few thunderstorms across the western portion of the state in an unstable southerly wind pattern tonight. Meanwhile, more stable conditions are forecast over the eastern islands as a weak ridge and southeasterly winds limit shower activity. The front will weaken into a trough and lift northwestward back over Kauai County on Thursday, providing continued shower chances over the western end of the state, with improving weather trends for Molokai and Oahu. Ridging aloft will then slowly build back in over the islands as the trough north of the state fills in and lifts northward, marking a return of more stable easterly trade wind weather this weekend. These more typical and stable moderate to breezy trade winds with brief windward and mountain showers will last through Christmas Day.

Discussion

An active weather pattern continues across the western portion of the state this afternoon as a front remains stalled near Kauai. A meandering band of showers thunderstorms has been moving over and near Kauai for much of the day today, bringing repeated rounds of moderate to locally heavy rain. Rain gauges and radar estimated QPE shows that portions of Kauai, in particular the southern and eastern portions of the island near Lihue and surrounding areas, have received in excess of 2 inches of rain since this morning. When combined with rainfall that also fell last night and during the early morning hours, widespread 24 hour rainfall totals between 1 to 3 inches have been measured across the Garden Isle. Fortunately, due to the progressive nature of the heaviest showers within the band of moisture, flooding has been predominantly localized and impacts minimized thus far in the event. For Oahu, showers have been fewer throughout the day, though areas of West Oahu and the North Shore did pick up decent rainfall totals earlier this morning. Much drier conditions are observed across Maui County and the Big Island, though terrain- influenced gusty southerly flow has been observed at both Kahului and Hilo this afternoon.
From this evening into Thursday, expect cloudy skies, periods of moderate to locally heavy showers, and a few thunderstorms to continue across Kauai County, Oahu, and surrounding waters as unstable deep tropical moisture continues to be introduced over the western half of the state in the vicinity of the stalled frontal boundary and it's associated pre-frontal convergence. Of note, the latest hi-res and probabilistic guidance, as well as the various convection-allowing models (CAMs), continue to suggest that bands of potentially training showers (heavy at times) and isolated thunderstorms could move over Kauai and/or Oahu this evening and tonight. Confidence in exactly where the heaviest, or repeated, showers will set up is fairly low. While it is certainly possible that they could remain mostly over the water in the Kauai Channel for the majority of the night, it is nearly equally probable that they could begin training over the islands of Kauai or Oahu depending on the front's progress, potentially leading to flash flooding concerns. Therefore, the Flood Watch will continue through Thursday afternoon.
By later Thursday into Friday, the high pressure ridge aloft will slowly build back in over the islands as the remnants of the frontal boundary (now weakened to a trough) north of the state fills in and lifts northward. This will mark the return of more stable easterly trade wind weather for the weekend. However, clouds and showers will linger over the islands in Kauai County for one more day as the trough slowly drifts across the island. Inversion heights will be limited as the ridge builds back in, limiting cloud heights, and therefore, shower potential. These more typical and stable moderate to breezy trade winds with brief windward and mountain showers will last through Christmas Day.

Aviation

A weakening cold front near Kauai and a prefrontal wind convergence boundary over the Kauai Channel will continue to produce southerly winds and drive unstable tropical moisture across the western end of the state through Thursday. The front will stall near Oahu overnight into Thursday, then gradually weaken and lift northward back over Kauai. MVFR conditions are expected as low clouds, showers and even a few thunderstorms along and ahead of the front stream in across the western end of the state. Isolated IFR conditions will remain possible in the heavier showers and thunderstorms. The eastern half of the state will remain fairly stable and dry with prevailing VFR conditions.
AIRMET Sierra remains in effect for tempo mountain obscurations across Kauai and Oahu this evening. IFR conditions over Lanai have persisted through most of the day and are expected to continue into the evening.
AIRMET Tango is in effect for tempo moderate turbulence below 080 over and north through east of island terrain on Oahu and Molokai. This low level turbulence should decrease overnight.

Marine

A cold front just NW of Kauai will slowly drift closer and stall near or over Kauai tonight before getting pushed back to the NW tomorrow. Moderate to locally strong southerly winds over the western half of the state tonight should gradually decrease to moderate by Thursday morning. A Small Craft Advisory (SCA) remains in effect for seas to 10 ft through Thursday night due to the current WNW swell and incoming NW swell. Isolated thunderstorms and heavy showers remain possible mainly over Kauai and Oahu waters through Thursday. A strong high pressure system will build N of the state Friday allowing light to moderate trades to return and gradually strengthen to moderate to strong speeds Sunday into early next week.
A moderate to large, medium period WNW swell (280 to 320 degrees) and NW swell have come in above guidance and will hold through the rest of the afternoon before decreasing late tonight. Then a slightly larger, medium period NNW (330-350 degree) swell will fill in late tonight and peak Thursday right around advisory levels. These swells will keep advisory level surf in place for north and west shores through Thursday and will gradually decline Friday. By Saturday morning, a N swell looks to move in and peak at around advisory levels, then gradually decrease Sunday through early next week.
E shore surf will remain small except where NW-N swell energy wraps through the rest of the week. By next week, a large, short period NE swell could elevate surf along E facing shores as strong trade winds return. Current model discrepancies highlight uncertainty in the timing of the higher E surf, with some models showing large surf by Tuesday, while others Wednesday. S shore surf will remain choppy as persistent S-SW winds hold through today, before gradually easing through the rest of week. Small background SW swells will keep surf from going flat through the weekend.

Fire weather

Wet weather conditions and isolated thunderstorms will continue into Thursday across the western islands. Periods of clouds and scattered showers are expected for Molokai and Lanai, with drier conditions remaining in place over Maui and the Big Island. Trade winds and increasingly stable conditions will slowly return to the western half of the state from Friday into the weekend. Wind speeds and humidity levels will keep weather conditions below critical fire thresholds throughout the next week.

HFO Watches/Warnings/Advisories

Flood Watch through Thursday afternoon for Niihau, Kauai, and Oahu.
High Surf Advisory until 6 AM HST Friday for north and west facing shores of Niihau, Kauai, and Oahu.
High Surf Advisory from 6 AM Thursday to 6 AM HST Friday for north and west facing shores of Molokai, and north facing shores of Maui.
Small Craft Advisory until 6 AM HST Friday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel.
Small Craft Advisory from midnight tonight to 6 AM HST Friday for Maui County Windward Waters.

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Data Courtesy of NOAA.gov