Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly sunny. Scattered showers in the late morning and afternoon. Highs 79 to 84 near the shore to around 71 above 3000 feet. Light winds. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 69 near the shore to around 58 above 3000 feet. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 79 to 84 near the shore to around 70 above 3000 feet. Light winds becoming southwest up to 10 mph in the afternoon. Chance of rain 50 percent.

South Kaua’i

Today: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 82. Light winds. Chance of rain 30 percent.

Tonight: Partly cloudy with isolated showers. Lows around 67. Northeast winds up to 10 mph. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 80 to 85. Northeast winds up to 10 mph shifting to the east around 10 mph in the afternoon. Chance of rain 40 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs 71 to 78 in the valleys to around 65 above 4000 feet. Light winds. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 66 in the valleys to around 57 above 4000 feet. Light winds. Chance of rain 40 percent.

Thursday: Partly sunny. Scattered showers in the morning, then showers likely in the afternoon. Highs 71 to 78 in the valleys to around 64 above 4000 feet. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 60 percent.

North Kaua’i

Today: Partly sunny with scattered showers and isolated thunderstorms in the morning, then mostly sunny with isolated showers in the afternoon. Highs 72 to 81. Northeast winds up to 10 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy. Isolated showers early in the evening, then scattered showers in the late evening and overnight. Lows 61 to 69. Light winds. Chance of rain 40 percent.

Thursday: Partly sunny. Scattered showers in the morning, then showers likely in the afternoon. Highs 72 to 81. Southeast winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 60 percent.

East Kaua’i

Today: Mostly sunny with isolated showers early in the morning, then mostly sunny with scattered showers in the late morning and afternoon. Highs 73 to 83. Northeast winds up to 10 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with scattered showers. Lows 61 to 71. Light winds. Chance of rain 40 percent.

Thursday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 72 to 83. Northeast winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light winds will prevail for the next couple of days, with the island atmosphere somewhat unstable. Low clouds will generally clear over the islands during the night and morning, with afternoon sea breezes leading to cloud and shower formation over island interiors. Unstable trade winds will develop Friday through Sunday with locally heavy rainfall and isolated thunderstorms possible over some islands. Stronger and more stable trades develop by next week.

Discussion

The mid-level low that brought periods of heavy rain to the area over the weekend and earlier this week is seen on morning IR imagery drifting southwestward about 600 miles SW of Honolulu. The remnant moisture field over the islands has become more disorganized and fractured due to descending mid-level dry air lifting through Maui County and Oahu. Deeper low-level moisture resides in the vicinity of Kauai where light trade winds will favor occasional showers over windward slopes through Thursday. Southwesterlies wrapping around the eastern periphery of the low will supply a steady feed of cirrus over the eastern end of the state, but degrading moisture quality has brought an end to last evening's rain over the Big Island. At present, dry conditions prevail nearly everywhere courtesy of overnight land breezes.
Little change is expected this afternoon compared to yesterday. The aforementioned mid-level dry air will provide strong stability over the central islands which will limit the intensity of any interior showers there this afternoon. Meanwhile, convective potential over the Big Island will likely be limited by extensive high clouds, though isolated thunder is still possible by this afternoon. By Thursday, a slight strengthening of the gradient near Kauai brings an uptick in trade wind showers while clearing high clouds yields better potential for afternoon over the Big Island. Sea breezes may be slightly more productive over the central islands on Thursday afternoon, but stagnant mid-level dry air will continue to provide capping there.
Friday through Sunday will be characterized by strengthening trades as amplified and very broad longwave ridging works across the North Pacific Basin. At the same time, the aforementioned mid-level low will weaken and shear northeastward bringing a brief period of modest large scale forcing and a reduction in stability centered on Friday and Saturday. A period of wet and modestly unstable trades is anticipated during this time with locally heavy rainfall possible, mainly over windward and mauka zones. There is increased interest in this period for the western end of the state where low-level convergence will serve as a focus for deeper moisture and a band of more persistent & potentially heavy showers. As 500mb temperatures cool through the first half of the weekend, steepening lapse rates will favor pockets of thunderstorms developing within this band. As usual, the position and expected movement (or lack thereof) of the heavier rain band represent the primary sources of uncertainty. At this time, the EC is more progressive and results in a more even rainfall distribution while multiple runs of the GFS focus the heaviest rain over Kauai for a full 36-48 hours and suggests elevated flooding potential.
The low will be gone for good no later than Monday as it shears back into the prevailing westerlies. Consensus among the global models remains solid that a more stable breezy trade wind pattern will take hold for most or all of next week.

Aviation

Light winds will support early morning land breezes and daytime sea breezes today due to a surface trough in the area. Although VFR conditions will prevail through much of the period, afternoon showers could become heavy at times and lead to MVFR CIGS/VSBYS today. In addition to the potential for localized heavy showers, a thunderstorm or two can't be ruled out over the Big Island slopes this afternoon due to the added instability with the upper low nearby.
AIRMET Tango for moderate mid- and upper-level turbulence remains in effect due to the proximity of the upper low. These conditions are expected to persist today.

Marine

Light winds will prevail over the marine area through Thursday night as surface troughing lingers in the vicinity of the islands. Trade winds will begin to strengthen as high pressure builds north of the state on Friday. Fresh to strong trades are then expected this weekend, with Small Craft Advisories likely across the typically windy waters around Maui and the Big Island.
A series of small northwest swells (310-320 degrees) will keep surf relatively steady through Thursday, with a slow decline expected Friday and Saturday. A small north-northwest swell (340-350 degrees) is expected to build late Saturday and Saturday night then slowly decline as it shifts more northerly (360-010 degrees) Sunday through Monday. A new long period northwest swell (320 degrees) is expected to slowly build to moderate levels Monday through next Tuesday.
An out of season south swell will provide surf around summertime average through Thursday, with a slow decline expected Friday through Saturday. Mainly background south swell energy and small surf is expected along south facing shores Sunday through early next week.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov