Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly cloudy. Breezy. Scattered showers in the afternoon. Highs 77 to 83 near the shore to around 69 above 3000 feet. East winds up to 15 mph shifting to the southeast in the afternoon. Chance of rain 30 percent.

Tonight: Breezy. Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Lows 64 to 69 near the shore to around 58 above 3000 feet. South winds 10 to 25 mph with gusts to 45 mph. Chance of rain near 100 percent.

Thursday: Windy. Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Highs 77 to 83 near the shore to around 68 above 3000 feet. Southwest winds 15 to 30 mph. Gusts up to 45 mph increasing to 60 mph in the afternoon. Chance of rain near 100 percent.

South Kaua’i

Today: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 74 to 82. East winds up to 10 mph. Chance of rain 30 percent.

Tonight: Breezy. Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Lows around 68. South winds 10 to 20 mph. Chance of rain near 100 percent.

Thursday: Windy. Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Highs 74 to 82. Southwest winds 20 to 30 mph. Chance of rain near 100 percent.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 69 to 76 in the valleys to around 60 above 4000 feet. Southeast winds up to 10 mph shifting to the south up to 20 mph in the afternoon. Chance of rain 30 percent.

Tonight: Windy. Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Lows 58 to 67 in the valleys to around 56 above 4000 feet. South winds up to 30 mph increasing to 10 to 35 mph after midnight. Chance of rain near 100 percent.

Thursday: Very windy. Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Highs 69 to 76 in the valleys to around 61 above 4000 feet. Southwest winds 20 to 35 mph with gusts to 55 mph becoming 15 to 45 mph with gusts to 75 mph in the afternoon. Chance of rain near 100 percent.

North Kaua’i

Today: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 72 to 80. Southeast winds up to 15 mph. Chance of rain 30 percent.

Tonight: Windy. Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Lows 61 to 68. Southeast winds up to 30 mph shifting to the south 10 to 30 mph after midnight. Gusts up to 50 mph. Chance of rain near 100 percent.

Thursday: Windy. Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Highs 71 to 79. Southwest winds 10 to 30 mph with gusts to 55 mph. Chance of rain near 100 percent.

East Kaua’i

Today: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 68 to 79. Southwest winds up to 15 mph shifting to the southeast in the afternoon. Chance of rain 30 percent.

Tonight: Breezy. Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Lows 61 to 70. South winds 10 to 25 mph. Chance of rain near 100 percent.

Thursday: Windy. Occasional showers and chance of thunderstorms. Locally heavy rainfall possible. Highs 68 to 80. Southwest winds 15 to 30 mph. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

Cool and pleasant conditions will linger early this morning before quickly transitioning through the day today as winds shift out of the south-southeast ahead of a strengthening low approaching from the northwest. This strong winter low pressure system will pass just north of Kauai on 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 accompany the front. Conditions will quickly improve behind the front Friday night into the weekend, continuing through early next week.

Discussion

Mostly dry and cool conditions will linger early this morning, with dewpoints hovering in the 50s for most areas. The best chance for any light showers will be over the far eastern end of the state, where a residual moisture axis associated with an old front remains.
A quick transition period is anticipated through the day in response to strong low pressure approaching from the northwest. The low-level flow will quickly respond and increase, while veering out of the south to southeast through the day, drawing warm and moist air northward. Dewpoints will surge into the mid to upper 60s by the end of the day. Isentropic upglide combined with the moistening boundary layer will support increasing rain chances by the end of the day, mostly in the form of isolated to scattered afternoon showers favoring south through east facing slopes.
Guidance remains in good agreement and depicts an active weather pattern unfolding late tonight through early Friday, with strong surface low pressure passing nearby to the north and its attendant cold front advancing down the island chain. Kinematic (0-6 km bulk shear values of 35-45 kt, with up to 40-50 knot winds at 850 mb) and thermodynamic profiles (MUCAPE of 1500-2000 J/kg) continue to support a potential significant event evolving across the state, with impacts ranging from damaging southwest winds (downsloping into north thru windward sections), to strong to severe thunderstorms and flash flooding. Additionally, deep convection will support the potential for periods of heavy snow over the Big Island Summits late Thursday through Friday.
Conditions will quickly improve over the weekend as the upper trough and surface low lift northeastward and away from the region and high pressure builds in its wake.

Aviation

Moderate easterly winds should veer southeast today due to a low pressure NW of the islands getting closer. A few SHRA with MVFR conds should favor windward and mauka locations today.
As the aforementioned low pressure passes to the north of the islands, a strong cold front will push down the island chain late tonight through Friday. Expect conds to deteriorate to MVFR/IFR or worse with high and gusty winds, heavy rain and thunderstorms all possible.
AIRMET Sierra is in effect for mtn obsc for windward Big Island. This should improve in the morning hours. As this next system moves in expect this to go back into effect.
AIRMET Tango is not in effect but may be needed later tonight as this next system moves in.

Marine

A strong low pressure passing eastward through the region will increase the threats of strong thunderstorms, gale-force winds, and periods of heavy rain across the state. Wind threats will include strong to gale force southwest wind speeds from tonight through Thursday with erratic and damaging wind gusts possible near any thunderstorms. A cold front will also move across the islands during this time period. Gentle to fresh westerly to northwesterly winds will build in rapidly behind the front along with improving marine weather trends. Marine Weather Warnings are likely during this time due to the high potential for strong thunderstorms. A Gale Watch remains in effect for the waters around Kauai from tonight through Thursday. A Small Craft Advisory will also be needed for all remaining Hawaiian coastal waters during this time period.
A new north-northwest swell will peak this 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 building in by next week Monday and then peaking by Tuesday.
Surf along south-facing shores will remain small today. Rough and choppy surf will develop along south and west facing shores from tonight through Friday due to the strong south to southwesterly kona winds developing from the passing low pressure system.

Fire weather

Critical fire weather conditions not expected through the forecast period.

HFO Watches/Warnings/Advisories

High Wind Watch from this evening to 6 AM HST Friday for all Hawaiian Islands.
High Wind Watch from this evening to 6 AM HST Friday for Haleakala Summit.
High Wind Warning from noon today to 6 AM HST Friday for Big Island Summits.
Winter Storm Watch from late tonight through Friday morning for Big Island Summits.
Gale Watch from this evening through Thursday afternoon for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel.

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