Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny. Scattered showers early in the morning. Locally heavy rainfall possible early in the morning. Highs around 82 near the shore to around 73 above 3000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Lows 61 to 66 near the shore to around 52 above 3000 feet. North winds up to 10 mph in the evening becoming light.

Thursday: Mostly sunny with isolated showers. Highs around 84 near the shore to around 74 above 3000 feet. Southwest winds up to 10 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly sunny. Scattered showers early in the morning. Locally heavy rainfall possible early in the morning. Highs around 81. West winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy. Lows 59 to 65. North winds up to 10 mph in the evening becoming light.

Thursday: Mostly sunny with isolated showers. Highs around 82. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 20 percent.

Kaua’i Mountains

Today: Partly sunny early in the morning then becoming mostly sunny. Scattered showers early in the morning, then isolated showers in the late morning and afternoon. Locally heavy rainfall possible. Highs around 76 in the valleys to around 65 above 4000 feet. Southwest winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Lows around 55 in the valleys to around 47 above 4000 feet. Light winds.

Thursday: Mostly sunny with isolated showers. Highs around 77 in the valleys to around 66 above 4000 feet. Light winds. Chance of rain 20 percent.

North Kaua’i

Today: Partly sunny early in the morning then becoming mostly sunny. Breezy. Scattered showers early in the morning, then isolated showers in the late morning and afternoon. Locally heavy rainfall possible. Highs 76 to 82. West winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Lows 55 to 64. West winds up to 15 mph in the evening becoming light.

Thursday: Mostly sunny with isolated showers. Highs 77 to 83. Light winds becoming northeast around 10 mph in the afternoon. Chance of rain 20 percent.

East Kaua’i

Today: Partly sunny early in the morning then becoming mostly sunny. Scattered showers early in the morning, then isolated showers in the late morning and afternoon. Locally heavy rainfall possible. Highs 74 to 80. Southwest winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Lows 53 to 66. West winds up to 10 mph in the evening becoming light.

Thursday: Mostly sunny with isolated showers. Highs 75 to 81. Northeast winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Convective shower bands are developing ahead of a cold front, currently near Kauai, are currently moving through Oahu and into the islands of Maui County this morning. Threats for heavy rain, flooding and thunderstorms are possible mainly ahead of this front affecting Oahu through sunrise this morning, and spreading eastward across islands in Maui County and the Big Island today through Thursday. More stable conditions with westerly winds will fill in rapidly behind the front for the western half of the state. East to southeasterly winds will develop across the region on Friday and Saturday with isolated to scattered showers forecast into early next week as another cold front approaches the islands from the northwest.

Discussion

Starting with the infra-red satellite imagery this morning, we see a band of convective showers moving through Oahu and spreading eastward into Maui County. Expect rain for all islands except Kauai County today, heavy at times, with the potential for isolated thunderstorms. The heaviest showers last night over Oahu were ranging from 2 to 3 inches an hour based on both rain gauges and radar rainfall estimates. Southeasterly winds over the Big Island also produced a band of persistent moderate to heavy rainfall along southeastern slopes across typically drier areas of the Ka'u and Puna Districts last night. Overnight rainfall as measured by both radar and local rain gauges in the area reported total rainfall amounts between 2 to 10 inches.
Southerly winds have already produced strong wind gusts to around 50 MPH in some locations north of island mountains on Oahu and Molokai. Peak wind gusts from 40 to 50 MPH are possible today for the same terrain favored areas along northern slopes in Maui County today with near 40 MPH gusts possible over some areas on the Big Island.
The Flood Watch was cancelled for Kauai County this morning as more stable conditions are moving in behind the passing cold front. The Flood Watch remains in effect for all other islands this morning. This Flood Watch coverage will likely be trimmed back from west to east today as the cold front passes through each island and more stable conditions behind the front cause the flooding threat to diminish.
More stable conditions will develop rapidly behind the front as it passes through the western islands through the day. Winds will veer from a more westerly direction with drier conditions and decreasing shower activity spreading from west to east. Weather conditions will likely improve over Kauai, Niihau and Oahu by sunrise this morning. The frontal band and convective showers will weaken as it passes through each island with front stalling and dissipating near Maui and the Big Island on Thursday. A high pressure ridge will then build in from the northeast, briefly strengthening the trade winds, and pushing lingering showers back westward across Molokai, Oahu, Kauai and Niihau on Friday and Saturday. East to southeast winds return later this weekend as another cold front approaches the islands from the northwest weakening the ridge north of the island chain.

Aviation

A front currently between Kauai and Oahu will move to Maui County and the Big Island today and tonight while gradually weakening. The threat of heavy showers and gusty winds will be ending over Kauai shortly, and over Oahu this morning, while widespread MVFR CIG/VIS and isolated IFR CIG/VIS can be expected over Maui County and the Big Island into tonight.
While overnight thunderstorm coverage has been limited to isolated, heavy showers have produced widespread wind gusts near 40 kt over parts of Oahu and Maui County over the past several hours. The potential for strong and erratic winds, mainly with heavy showers and any thunderstorms that develop, will continue over Maui County and the Big Island through at least this morning, gradually diminishing later today and tonight as the front stalls and weakens near and E of the Big Island. Associated AIRMETs will be adjusted and updated as conditions warrant.

Marine

Latest radar imagery shows the band of moderate to locally heavy showers that was centered over the Kauai Channel last night from the southwest to the northeast is now moving over Maui County. This band of showers is associated with an advancing cold front that is currently moving over Kauai channel and will continue to move eastward across Oahu and the central smaller islands today before weakening and stalling across the eastern end of the state Thursday. Fresh to strong south winds and rough seas will also continue across waters along and ahead of the front today and into Thursday. Thunderstorms continue over the offshore waters (around 100 nm north of Oahu) in advance of the approaching front.
Winds and seas have already dropped off quickly for Kauai and should drop by early afternoon today for Oahu waters, then by tonight for Maui and the Big Island. Winds will become north to northeast Thursday through Friday for all waters as weak high pressure builds to the north. The Small Craft Advisory has been scaled back to waters east of Kauai, excluding Big Island southeast waters through Wednesday afternoon, some zones may continue to be dropped later this afternoon as winds relax behind the front.
Surf along north and west facing shores will trend up today as a small to moderate west-northwest medium period swell fills in. This swell will peak Thursday, then ease Friday. A long-period northwest swell from a distant source in the far northwest Pacific is forecast to arrive Friday night, build through the day Saturday, then peak Saturday night into Sunday before easing.
Surf along south facing shores will become rough and choppy through today due to the aforementioned strong south winds associated with the cold front moving through. This will quickly lower by Thursday as the winds ease. A long-period south swell will arrive Friday night, peak over the weekend, before slowly subsiding into early next week.
Surf along east facing shores will remain small through early next week.

HFO Watches/Warnings/Advisories

Flood Watch through this afternoon for Oahu, Molokai, Lanai, Maui, Kahoolawe, and the Big Island.
Small Craft Advisory until 6 PM HST this evening for waters and channels around Oahu, Maui and the Big Island.

Data Courtesy of NOAA.gov