Photo Credit: Sebastien Gabriel

West Kaua’i

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South Kaua’i

Today: Cloudy and breezy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs around 79. East winds 15 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 66 to 71. East winds 15 to 20 mph. Chance of rain 50 percent.

Thursday: Breezy. Mostly cloudy with scattered showers. Highs around 79. East winds 15 to 20 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Cloudy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 69 to 76 in the valleys to around 60 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 64 in the valleys to around 52 above 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

Thursday: Breezy. Mostly cloudy with scattered showers. Highs 69 to 76 in the valleys to around 60 above 4000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

North Kaua’i

Today: Cloudy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 72 to 82. Southeast winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 70. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Thursday: Breezy. Mostly cloudy with scattered showers. Highs 72 to 82. East winds up to 20 mph. Chance of rain 40 percent.

East Kaua’i

Today: Cloudy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 72 to 81. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 72. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Mostly cloudy with scattered showers. Highs 72 to 81. East winds 10 to 15 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Trade winds return today as the low pressure system west-northwest of the Hawaiian Islands continues to drift westward away from the state. Periods of showers are possible today, mainly over the western half of the state through the morning hours. Isolated thunderstorms remain in the forecast today for Kauai County and over interior sections of the Big Island in the afternoon hours. A high pressure ridge builds back in north of the region today and tomorrow, strengthening trade winds into the breezy to locally windy range into the weekend. Passing showers will trend back to the typical windward and mountain areas from Wednesday afternoon onward.

Discussion

An upper level cut off low roughly 600 miles west-northwest of Kauai continues to drift westward this morning. A convergence band of thunderstorms associated with this upper low lingers roughly 200 miles west of the state. Enough instability remains near Kauai for continued periods of showers and a few thunderstorms remain possible this morning. Upper air balloon soundings from Hilo and Lihue show subsidence temperature inversion heights around 7,500 feet and 8,500 feet respectively. These temperature inversion heights should drop through the day today as stabilizing subsidence increases across the region. The Flood Watch for Kauai County was cancelled this morning as the threat for flash flooding has decreased below our watch thresholds.
The weather pattern will transition today from an east to southeast wind pattern into a moderate to breezy easterly trade winds. More stable conditions will return as the low exits to the west and the subtropical high builds in to the north of the island chain. Trade wind inversion heights will range from 6,000 to 8,000 feet over the next few days which will allow typical passing windward and mountain showers, favoring the overnight to early morning hours, with drier conditions expected over leeward areas. Wind speeds will increase on Thursday into the breezy to locally windy trade wind range as high pressure continues to build north of the state. These stronger trade winds will likely last into the weekend.
More stable conditions are in the forecast from Monday through next Wednesday with moderate to breezy trade winds and brief windward and mountain showers. Scattered high level cirrus clouds will enhance sunrise and sunset colors.

Aviation

An upper-level low slightly more than 550 miles west-northwest of Kauai is drifting slowly westward. The proximity of this feature will likely maintain an unstable east-southeast flow over far the western end of the island chain this morning. Clouds with embedded scattered showers and a slight chance of thunderstorms will likely remain in the vicinity of Kauai today. This may result in periods of MVFR conditions, with isolated IFR conditions, over Kauai.
Elsewhere, a surface high pressure system far northeast of the state is moving slowly westward. This is causing the pressure gradient to begin to tighten over the eastern end of the island chain. As a result, expect strengthening trade winds to spread from east to west across the state through this afternoon. The return of the trade winds will also usher in more stable atmospheric conditions later today. In the meantime, low clouds and brief showers may continue to move over east facing sections of the island chain from Oahu to the Big Island. Note that there is a slight chance of thunderstorms over upslope sections of the Big Island during the time of maximum heating this afternoon. Brief MVFR conditions may occur along east facing sections of the islands east of Kauai. Otherwise, expect VFR conditions to prevail across most of the eastern two-thirds of the island chain.
By this evening, the increasingly stable easterly trade winds will likely cover most of the state, including Kauai. Therefore, a return to a more typical trade wind weather pattern is expected from this evening through Thursday morning.
No AIRMETs are currently in effect, and none are anticipated this morning. There is a slight possibility that AIRMET Sierra may be needed if mountain obscuration develops on Kauai later today.

Marine

A surface trough is nearing the state from the northwest. This approaching trough has recently assisted in initiating scattered thunderstorms within a more unstable environment over the offshore waters west of Kauai. High pressure will move in north of the state the next couple of days. This will begin a period of more typical trade winds the next several days. Moderate easterlies will become locally strong through the notoriously windier marine zones surrounding Maui County and Big Island. A Small Craft Advisory (SCA) for these typically windier waters will be in effect today. This SCA will likely need to be expanded in areal coverage and extended in time as fresh to strong trade winds persist into the weekend.
The moderate size, medium to long period northwest swell (310 degree) that filled in around the islands yesterday will gradually be declining through Thursday. This has allowed the High Surf Advisory (HSA) for those shores to expire this morning. Surf along south-facing shores will be elevated the next several days with the arrival of a couple of near 4 to 5 foot, longer period south southwest swells (180-200 degree). The first south southwest swell coming in today will increase south-facing surf heights to HSA levels through at least early Thursday. The next south swell (180 degree) is timed to arrive later in the week. East-facing shore wind wave chop will remain small through the day but will rise later this week as east trades return and restrengthen over and upstream of the island chain.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Thursday for south facing shores of all Hawaiian Islands.
Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov