West Kaua’i

Today: Mostly sunny with isolated showers. Highs around 83 near the shore to around 72 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows around 69 near the shore to around 59 above 3000 feet. East winds around 10 mph. Chance of rain 20 percent.

Thursday: Partly sunny with isolated showers. Highs around 83 near the shore to around 72 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

South Kaua’i

Today: Partly sunny with scattered showers. Highs 76 to 83. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 69. East winds 10 to 15 mph. Chance of rain 40 percent.

Thursday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 84. Light winds becoming southeast around 10 mph in the afternoon. Chance of rain 30 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs 71 to 79 in the valleys to around 63 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 61 to 68 in the valleys to around 58 above 4000 feet. East winds around 10 mph. Chance of rain 50 percent.

Thursday: Mostly cloudy with scattered showers. Highs 73 to 78 in the valleys to around 64 above 4000 feet. Southeast winds up to 10 mph in the morning becoming light. Chance of rain 40 percent.

North Kaua’i

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 73 to 83. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 62 to 71. East winds 10 to 15 mph. Chance of rain 30 percent.

Thursday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 74 to 83. Southeast winds up to 10 mph. Chance of rain 40 percent.

East Kaua’i

Today: Mostly cloudy with scattered showers. Highs 69 to 81. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 63 to 73. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Mostly cloudy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 71 to 82. Southeast winds around 10 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Surface high pressure northeast of the state will continue to bring locally breezy easterly trade winds today. Brief passing showers will favor mainly windward and mountain areas this morning and again tonight. Thursday through this weekend, trade winds will ease slightly and veer to a more east- southeast direction as a front stalls northwest of the region. This will help focus shower activity along east and southeast facing slopes and interior regions of most islands during the afternoons. However, overall rainfall amounts are expected to remain limited. An approaching front may bring breezy southerly flow and unsettled wet weather by early to mid- next week.

Discussion

A 1031 mb surface high positioned well northeast of the state helped maintain moderate to locally breezy easterly trades last night into early this morning. RADAR has been fairly quiet with isolated light showers affecting mainly windward locations. Several windward and mauka stations have reported accumulation, though generally below a tenth of an inch. Expect little change in the overall pattern today as the aforementioned surface high slowly drifts eastward. After a brief lull in shower activity this afternoon, there should be an uptick in coverage again after sundown.
Thursday through this weekend, a cold front approaching the islands from the northwest will allow easterly trades to weaken and veer east southeasterly. In this regime, showers tend to favor southeast and east facing slopes of the Big Island and Maui, along with interior portions of the other islands due to the development of afternoon sea breezes in the lighter, blocked flow. Model guidance stalls the front west of the state, then eventually lifts it to the north.
Early next week, another cold front will approach Hawaii from the northwest. Ahead of this feature, flow will veer more southerly and begin to advect deep tropical moisture into the region. By mid week, both the GFS and ECMWF agree in deepening this unstable moisture band across the state, especially over the western islands. However, there is still much uncertainty in strength and timing of this next storm. The GFS generates a much stronger system with a deeper parent surface low and greater upper level support. The ECMWF depicts a weaker parent low, less moisture, and a majority of the upper level forcing residing farther north of the state. Though the potential for heavy rain, thunderstorms, and strong southerly winds exists, details will need to be ironed out in the next few days as models come in better agreement.

Aviation

Moderately breezy trades are expected throughout the TAF period. Spotty shower activity is possible along windward and mountain sites, with periods of MVFR conditions possible. Elsewhere, expect VFR conditions to prevail.
AIRMET Tango remains in effect for turbulence below 8 kft along leeward sites of the islands due to the ongoing trade pattern. This is expected to remain in effect through the period.

Marine

Trade winds will strengthen into the fresh to strong range and become increasingly easterly today as surface high pressure strengthens far northeast of the islands. Tonight into Thursday, winds will veer out of the east-southeast around Oahu and Kauai as the high drifts eastward and a front approaches the state from the northwest. A Small Craft Advisory (SCA) remains in effect for most of the waters around the Big Island and Maui through Thursday morning where winds will be strongest. The SCA has been extended through Thursday evening for the waters around the Big Island and Alenuihaha Channel as winds further north weaken slightly as they veer. Portions of the coastal waters will continue to see SCA conditions through the weekend. Local winds may veer from a more southerly direction early next week, as a cold frontal low slowly advances toward the islands from the west.
A small northwest swell will continue to decline through Thursday. A new small overlapping west-northwest swell will arrive late Thursday and hold through the weekend, which will cause another bump up in surf along north- and west-facing shores. This will be followed by another small west-northwest swell early next week. There may also be very small northerly swell late this week into the weekend. Choppy east shore surf will builds to near seasonal average today as trade winds strengthen over and east of the islands. Little change is expected along east facing shores through the weekend, followed by a possible decline early next week as winds veer increasingly southerly. Surf along south facing shores will remain small to tiny through the weekend, and some islands may see an increase in choppy surf if southerly winds develop early next week.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov