Photo Credit: Braden Jarvis

West Kaua’i

Today: Partly sunny with scattered showers. Highs around 84 near the shore to around 73 above 3000 feet. East winds up to 15 mph shifting to the southeast in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 67 near the shore to around 55 above 3000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Thursday: Breezy. Cloudy with scattered showers. Highs around 84 near the shore to around 74 above 3000 feet. East winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

South Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 79. East winds 10 to 15 mph shifting to the southeast in the afternoon. Chance of rain 60 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 67. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Cloudy and breezy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 79. Northeast winds 10 to 20 mph. Chance of rain 60 percent.

Kaua’i Mountains

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 80 in the valleys to around 64 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 63 in the valleys to around 52 above 4000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Thursday: Cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 77 in the valleys to around 66 above 4000 feet. Southeast winds up to 15 mph. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 76 to 83. Southeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 69. Southeast winds up to 15 mph. Chance of rain 50 percent.

Thursday: Cloudy with scattered showers. Highs 76 to 84. Southeast winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy with scattered showers. Highs 74 to 81. Southeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 70. South winds up to 10 mph shifting to the southeast after midnight. Chance of rain 50 percent.

Thursday: Cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 74 to 79. East winds up to 10 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Winds will become more southeasterly today with seabreezes developing for smaller islands. A rapidly developing low pressure northwest of the islands will keep winds light to locally breezy and out of the southeast through the forecast period. The low could also bring the potential for increased showers, some heavy along with isolated thunderstorms to Kauai and adjacent waters late Thursday and Friday.

Discussion

The 12Z sounding shows the precipitable water (PWAT) values have dropped near to below an inch overnight, these obs match well with satellite and radar imagery which shows low scattered showers focused mainly along exposed windward areas. There is an area of enhanced clouds and slightly higher PWAT following this drier patch that could increase chances of clouds and showers for windward areas, especially for Big Island and Maui County later tonight. As winds turn more southeasterly this afternoon, hi-res models are also showing a band of showers moving up from the south over Kauai and Oahu along with daytime seabreezes.
Forecast remains on track with a surface low rapidly developing around 700 miles northwest of Kauai later today into Thursday. The proximity of this low will keep southeasterly winds over the state into the weekend. Big Island and Maui will place the smaller islands in the lee of the main flow which will allow for sea breezes to develop each afternoon and land breezes to develop each evening the evening. Beginning late tonight winds will strengthen out of the southeast as the low strengthens.
As the low strengthens and lingers northwest of the state, a rather weakly forced warm conveyor will draw north a plume of deep moisture (PWATs around 2″ over the western end of the state) beneath a modest cold pool aloft (500mb temps around -10C over Kauai). Pockets of heavy rain/isolated thunderstorms will be possible Thursday-Friday, mainly in the vicinity of Kauai, where southerly flow is particularly convergent or where terrain interactions can give showers a boost. A Flood Watch has been issued for Niihau and Kauai starting Thursday afternoon through Friday afternoon. Elsewhere, increased moisture and veering winds will support a few leeward showers from time to time, but lack of organization and forcing is expected to limit coverage from Oahu to the Big Island. Light/veered southerly flow at the surface is expected to continue into the weekend with localized land and sea breeze patterns. A convergence band may track westward over the state late in the weekend, increasing chances of clouds and showers over the state.

Aviation

Weakening high pressure to the distant NE and rapidly developing low pressure about 600 nm NW of Kauai will lead to a decreasing and veering low-level wind flow over parts of the islands today and tonight. Moderate to locally strong E winds will persist over the Big Island, while a trend toward lighter SE flow is expected over Kauai and Oahu. VFR conditions will prevail through tonight, with brief periods of isolated MVFR VIS/CIG in SHRA. Showers will mainly occur over windward areas, although localized afternoon sea breezes may drive some leeward cloud and shower development today.
A convergence band is expected to develop W of the islands tonight, and approach Kauai County on Thursday. Increased moisture moving over these islands from the S will bring the potential for widespread MVFR, and localized IFR, conditions in +SHRA/+TSRA.

Marine

Weakening high pressure to the distant NE and rapidly developing low pressure about 600 nm NW of Kauai will lead to a decreasing and veering low-level SE wind flow over Kauai and Oahu waters, while locally strong E winds are expected over Big Island waters the next couple of days. A Small Craft Advisory (SCA) has been issued for the Alenuihaha and Pailolo Channel as well as Maui windward waters as locally strong and terrain- accelerated E flow is expect through at least Thursday. The SCA will likely be extended and more zones will likely be added in tonight.
The low will remain nearly stationary NW of the islands for several days, then move slowly NE over the weekend. An associated convergence band is expected to move over Kauai waters on Thursday, then potentially linger for a few days before drifting eastward through the weekend. As the band drifts E, moderate winds will likely veer to the S and SW over Kauai and Oahu waters, with with lighter winds veering to the SE over the Big Islands.
A medium-period NNW swell has continued to rise overnight as the swell will look to plateau and hold through the day, then gradually diminish Thursday. Surf along east facing shores will remain somewhat elevated with short- period wind waves generated by an upstream fetch of fresh trade winds. Small S swells will support small surf along S facing shores the next couple of days. Over the weekend, the low NW of the islands could aim a significant NW swell that could arrive early next week.

HFO Watches/Warnings/Advisories

Flood Watch from Thursday afternoon through Friday afternoon for Niihau, Kauai,
Wind Advisory until 6 PM HST Thursday for Big Island Summits.
Small Craft Advisory until 6 PM HST Thursday for Maui County Windward Waters, Pailolo Channel, Alenuihaha Channel.

Data Courtesy of NOAA.gov