Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny. Scattered showers in the afternoon. Highs around 80 near the shore to around 68 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 66 near the shore to around 55 above 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Thursday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 79 near the shore to around 67 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 79. East winds 10 to 15 mph. Chance of rain 30 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 62 to 67. East winds 10 to 15 mph. Chance of rain 30 percent.

Thursday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 78. East winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs 67 to 75 in the valleys to around 62 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 55 to 60 in the valleys to around 49 above 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

Thursday: Partly sunny with scattered showers. Highs 66 to 74 in the valleys to around 61 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 72 to 79. Southeast winds up to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 58 to 67. East winds up to 15 mph. Chance of rain 40 percent.

Thursday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 71 to 78. Southeast winds up to 15 mph. Chance of rain 40 percent.

East Kaua’i

Today: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 72 to 79. East 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 56 to 68. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Partly sunny with scattered showers. Highs 71 to 78. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy east to east-southeast trades will prevail during the next few days. Rainfall chances will remain highest over windward and mauka locations, particularly during the overnight and early morning hours, with an afternoon shower possible over leeward sections each day. Increasing moisture and a return of breezy easterly trades will support greater windward shower coverage over the weekend through early next week.

Discussion

Currently at the surface, a 1026 mb high is centered around 750 miles northeast of Honolulu, while a area of low pressure is positioned around 1350 miles west-northwest of Kauai. Light to moderate trades prevail in unsheltered areas early this morning, strongest over the eastern end of the state. Infrared satellite imagery shows variably cloudy skies across the state, with radar imagery showing scattered showers moving into windward slopes and coasts. Main short term focus revolves around trade wind trends and rain chances during the next few days.
High pressure northeast of the state will weaken today as a new strong high builds to the distant north. The high will strengthen while remaining anchored north of the islands Thursday and Friday as a low west of the state shifts eastward to a location between 800 and 1000 miles northeast of Kauai. Light to moderate east to east-southeasterly trades will hold in place tonight, then gradually strengthen back to moderate and locally breezy levels from east to west across the state by Thursday and Friday. Due to the east-southeasterly boundary layer flow, some localized leeward sea breezes will be possible in the more sheltered areas each afternoon. The low will dampen into a trough over the weekend while the strong high to the distant north settles southward and closer to the island chain. This will ramp the trades up to breezy levels statewide and shift the direction around to a more typical east-northeasterly direction. The strong high will hold north of the state early next week, before being reinforced by a new strong high to the distant north around the middle of next week. Breezy trades are expected to continue early next week, with windy conditions possible at times.
As for the remaining weather details, fairly dry trade wind weather will prevail during the next couple days as precipitable water (PW) values hold at or below 1 inch and mid level ridging remains parked overhead. Light showers will favor windward slopes and coasts, although an isolated afternoon shower will be possible over leeward areas with the assistance of localized sea breezes.
There remains some uncertainty on how far east a stacked low will make it late in the week, with the GFS further west than the ECMWF. The latest guidance suggests we could see an increase in windward showers Thursday night and Friday, particularly over the western islands, as some upper level forcing moves overhead and PW values rise above 1 inch. Timing details are more uncertain on a shallow moisture boundary associated with an old front moving through the state in the late Friday night through Saturday evening time frame. Beyond that, fairly typical trade wind weather can be expected Sunday through the middle of next week, with showers favoring windward and mauka areas and a few showers spilling leeward from time to time.

Aviation

Moderate east to east-southeast trades will continue, with the best rainfall chances remaining over windward and mauka locations through the early morning and overnight periods. Increasing cloud coverage along with a few light afternoon showers are possible over leeward areas today where localized sea breezes form. VFR conditions will prevail.
No AIRMETs in effect.

Marine

A surface high centered northeast of the islands will move slowly east today, with the associated ridge lingering in a position just north of Kauai. This will continue to support moderate to locally strong east to east-southeast winds around Maui County and the Big Island. Additional windward zones and Maalaea Bay have been added to the existing Small Craft Advisory (SCA) through Thursday. Lighter east to east-southeast winds will prevail elsewhere.
The combination of another high building far north of the islands and low pressure developing west of the state near the Papahanaumokuakea Marine National Monument will promote fresh to strong east to east-southeast winds Thursday into Friday, with the strongest winds over windward waters and around the Big Island.
Showers will be light and limited in coverage over the next several days. A convergence band associated with the low to the W may approach Kauai waters early this weekend while a shower band associated with a dissipated front arrives from the NE, increasing shower potential.
Surf looks to remain below High Surf Advisory (HSA) levels along all shores for the next several days. The current moderate long period northwest swell will see a slight increase through the morning hours before slowly declining Thursday. Reinforcement pulses of moderate, medium- to long- period northwest swells are expected over the next couple of days to keep surf elevated. A fast- moving but potent low now moving through the Aleutian Islands is generating what will be a moderate sized, long-period northwest swell filling in Saturday into Sunday with peak surf heights potentially reaching HSA levels. A strong, slow- moving low between Hawaii and California will lead to a potential for a medium period north- northeast swell filling in over the weekend into early next week. East facings shores will remain rough and choppy coinciding with the fresh to strong east to east-southeast winds over the next few days.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Thursday for Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov