West Kaua’i

Tonight: Mostly clear. Breezy. Lows around 67 near the shore to around 56 above 3000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph after midnight.

Tuesday: Sunny. Highs around 81 near the shore to around 68 above 3000 feet. Northeast winds up to 15 mph.

Tuesday Night: Mostly clear. Breezy. Lows around 66 near the shore to around 56 above 3000 feet. Northeast winds up to 20 mph.

South Kaua’i

Tonight: Partly cloudy. Breezy. Lows around 67. Northeast winds 10 to 20 mph.

Tuesday: Mostly sunny. Breezy. Highs 75 to 81. Northeast winds 15 to 25 mph.

Tuesday Night: Breezy. Partly cloudy with isolated showers. Lows around 66. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with isolated showers. Lows 59 to 65 in the valleys to around 54 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Tuesday: Breezy. Partly sunny with isolated showers. Highs 69 to 75 in the valleys to around 59 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Tuesday Night: Breezy. Mostly cloudy with scattered showers. Lows 58 to 64 in the valleys to around 54 above 4000 feet. Northeast winds up to 25 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy in the evening, then mostly cloudy with isolated showers after midnight. Lows 59 to 69. East winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs 70 to 81. East winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday Night: Partly cloudy with scattered showers. Lows 59 to 68. East winds 10 to 15 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Mostly cloudy with isolated showers. Lows 61 to 70. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Breezy. Isolated showers. Highs 68 to 79. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tuesday Night: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows 60 to 70. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

The active weather will start to taper off tonight as the triggering upper trough moves east of the state. As trade winds build in and strengthen, numerous windward showers expected Tuesday and Tuesday night before the remnant moisture moves west of the state. Expect drier trade wind weather Wednesday and beyond.

Discussion

Water vapor imagery shows an upper level trough moving across Hawaii this afternoon enhancing the band of moisture across the eastern half of the state left behind by the kona storm. Showers and thunderstorms have triggered on Oahu, Maui and Big Island today brought on by abundant moisture, cold temperatures aloft and steep lapse rates. The showers and thunderstorms are expected to wane tonight, but given the current active weather on the Big Island, will continue the Flood Watch for Big Island through early Tuesday morning. A Winter Weather Advisory is also posted for an additional 1 to 2 inches of snow on the Big Island summits above 12000 feet.
The upper trough will slide east of the state tonight with zonal flow expected over the next several days. Trade winds are building in and strengthening this afternoon, and will reach the Big Island by Tuesday morning. Expect breezy trade winds to continue through Wednesday night before weakening back to moderate levels. Windward showers will be numerous across Maui County and the Big Island through Tuesday as remnant moisture upstream gets directed back towards the state. However, with no upper level support, showers will become lighter. Scattered windward showers expected for Kauai and Oahu on Tuesday. The moisture will clear Maui County and Big Island by Wednesday morning, and expect to finally see drier trade wind weather through the end of the week.

Aviation

Lingering instability and moisture has triggered enhanced showers over windward areas of Oahu, and thunderstorm activity from Maui county to Big Island, bringing MVFR to isolated IFR conditions. Thunderstorms are still expected through the evening for windward Big Island, and are currently ongoing over southeast Big Island. The enhanced showers over Oahu are gradually weakening, and should diminish by tonight. The showers and thunderstorms over windward Big Island are expected to continue through the evening, but move offshore and diminish overnight. Recent thunderstorms have cleared Maui county, but lingering showers are still possible. Kauai remains VFR.
Expect MVFR conditions within showers from Oahu to Maui county, and MVFR to isolated IFR conditions for windward Big Island through tonight, with strengthening trade winds and increasing stability tomorrow.
AIRMET Sierra is in effect for mountain obscuration for Oahu, Maui county, and windward Big Island. Expect these conditions to improve over leeward areas tonight, but likely remain for windward areas. Light icing remains possible in layer 130-FL200 from Molokai through the Big Island, but conditions improve tomorrow as the mid-upper level clouds move out of the area.

Marine

A surface trough is lingering near the Big Island, and high pressure is building far north of the islands. A passing upper level disturbance will produce isolated strong thunderstorms along the trough through tonight, while northeasterly trade winds increase across the islands. A Small Craft Advisory (SCA) has been issued for all waters due to the increasing northeasterly winds. Winds will be strongest Tuesday and Tuesday night and are expected to ease Wednesday and Thursday, when the SCA will likely be decreased in coverage to the typically windy waters around the Big Island and Maui. Northeasterly trade winds may increase again Friday into the weekend, and the SCA may be expanded to additional waters.
A small, short period north swell will gradually decline tonight, while a small west-northwest persists. A reinforcing pulse of medium period north-northeast swell will arrive on Tuesday, peak in the afternoon and at night, then decline Wednesday. Surf along north and exposed east facing shores may near High Surf Advisory levels during the peak. Another small west-northwest swell will arrive Thursday, peak Friday, then decline during the weekend. Aside from areas along east shores exposed to the northerly swell, short period energy from rebuilding trade winds will increase to near seasonal average Tuesday night and Wednesday, then hold into the weekend. A small south-southwest swell will decline Tuesday and fade Wednesday. A short-lived pulse of small south-southeast swell will be possible Wednesday through Friday, and a small south- southwest swell could arrive Friday into the weekend.

HFO Watches/Warnings/Advisories

Flood Watch through late tonight for Kona, Kohala, Big Island Interior, Big Island South, Big Island Southeast, Big Island East, Big Island North.
Winter Weather Advisory until 6 AM HST Tuesday for Big Island Summits.
Small Craft Advisory until 6 AM HST Wednesday for all Hawaiian waters,

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Data Courtesy of NOAA.gov