Photo Credit: Braden Jarvis

West Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 73 to 79 near the shore to around 64 above 3000 feet. Northeast winds up to 15 mph in the morning becoming light. Chance of rain 20 percent.

Tonight: Mostly cloudy. Lows around 62 near the shore to around 52 above 3000 feet. Light winds becoming northeast up to 10 mph after midnight.

Wednesday: Partly sunny. Breezy. Scattered showers in the afternoon. Highs 77 to 83 near the shore to around 69 above 3000 feet. East winds 10 to 20 mph. Chance of rain 30 percent.

South Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Highs 70 to 78. Northeast winds 10 to 15 mph.

Tonight: Mostly cloudy with isolated showers. Lows around 63. Northeast winds around 10 mph. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 74 to 82. Northeast winds 10 to 15 mph shifting to the southeast in the afternoon. Chance of rain 30 percent.

Kaua’i Mountains

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 63 to 70 in the valleys to around 55 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy with isolated showers. Lows 52 to 61 in the valleys to around 50 above 4000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Partly sunny. 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 15 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 30 percent.

North Kaua’i

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 66 to 75. Northeast winds up to 15 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy with isolated showers. Lows 56 to 63. Light winds. Chance of rain 20 percent.

Wednesday: Partly sunny. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 72 to 80. Southeast winds up to 20 mph. Chance of rain 30 percent.

East Kaua’i

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 63 to 76. North winds around 10 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy with isolated showers. Lows 55 to 67. Light winds. Chance of rain 20 percent.

Wednesday: Partly sunny. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 68 to 79. Northeast winds up to 15 mph shifting to the southeast in the afternoon. Chance of rain 30 percent.

Detailed Forecast

Synopsis

Breezy and cool northerlies will weaken today and turn southeasterly on Wednesday. A potent winter low pressure system will develop west of the islands Wednesday night, pass by just north of Kauai on Thursday, then drag a cold front eastward through the islands Thursday night and Friday. This storm system will bring the threat of damaging south to southwest winds, flash flooding, and strong to severe thunderstorms Wednesday night through Friday. Much cooler and drier weather will move in behind the front Friday night and Saturday and continue through early next week.

Discussion

Currently at the surface, a cold front has just pushed just south of the Big Island early this morning, while strong high pressure continues to build in behind the front to the distant north- northwest. Meanwhile a developing storm system is located around 1400 miles west-northwest of Kauai. Breezy northerly winds have filled in behind the cold front. Infrared satellite imagery shows considerable cloud cover over windward slopes and coasts, with less cloud coverage in leeward locales. Radar imagery shows scattered showers affecting mainly windward areas behind the front, with coverage the highest over Big Island and Maui. The main short term focus revolves around rain chances today and wind trends today through Wednesday, with longer term attention remaining on the potential impacts from a very significant storm system moving through the islands Wednesday night through Friday.
The front will stall out and dissipate near the Big Island today and tonight, with the northerly winds gradually easing and shifting around to the east, while keeping most of the shower activity over windward sections of the Big Island. The frontal remnants will lift back northward through the islands on Wednesday with increasing south to southeasterly flow bringing a gradual increase in showers with the focus shifting around to south and southeast facing slopes and coasts.
Significant changes are in store for the islands beginning Wednesday night, as strong southerly winds bring a moist and unstable airmass northward in advance of a potent winter low developing several hundred miles northwest of Kauai. The low will shift eastward and pass by a couple hundred miles north of the Garden Isle Thursday, then drag a cold front eastward through the island chain Thursday night and Friday. In advance of the low and associated cold front, dewpoints will climb into the lower 70s, 0-1 km MUCAPE values rise to 1500-2000 J/KG, 0-6 KM Bulk Shear values hover in the 35-45 kt range. This will potentially bring severe thunderstorms, flash flooding in addition to the strong gradient winds (likely advisory and potentially warning level winds) to much of the island chain. The threat for adverse weather appears to begin Wednesday night and continue through Friday. Stay tuned for further updates as the event draws closer and timing details become more clear.
A Flash Flood Watch will likely be issued for the entire island chain later today. A Winter Storm Watch will likely need to be issued for the Big Island Summits later today or tonight. A High Wind Watch (gusts > 58 mph) will also likely be issued for portions of the island chain later today, including the high elevation summits of Haleakala and the Big Island.
Much drier and cooler weather will move in behind the front Friday night and Saturday, and continue through early next week.

Aviation

Breezy northerly winds with SHRA and low cigs expected across the the islands through the morning hours. MVFR/IFR conds are possible especially in any heavier SHRA. VFR should prevail outside of SHRA.
AIRMET Sierra remains in effect for mtn obsc for windward areas from Molokai to Big Island.
AIRMET Tango is in effect for low-level turb below 080 over and SE through SW of terrain for the smaller islands.

Marine

Fresh to locally breezy northerly wind speeds will decrease through the day and veer from a northeast direction by this afternoon as the front diminishes near the Big Island. A Small Craft Advisory (SCA) was decreased in coverage this morning to waters around Maui and the Big Island through noon HST. A northerly swell overlapping the locally generated wind waves will continue to produce rough surf along north and exposed east facing shores today.
A strong low pressure system and cold front moving through the islands from Wednesday night through Friday will bring fresh to strong southerly to southwesterly winds, periods of heavy rain, and strong thunderstorms. Wind gusts from these developing rain bands and thunderstorms will likely exceed gale force in some areas.
A north swell will continue through the week, followed by a larger northerly swell that may trigger a High Surf Advisory for north and exposed east facing shores from Friday into Saturday. Otherwise, surf along the east facing shores not exposed to northerly swells will remain small each day.
Surf along south-facing shores will remain small due to background south swells. Rough and choppy surf will develop along south and exposed west facing shores by Thursday and Friday as strong southerly winds increase locally generated wind waves into the region.

Fire weather

Conditions favorable for critical fire behavior are not expected during the forecast period.

HFO Watches/Warnings/Advisories

Small Craft Advisory until noon HST today for Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters.

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