Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly sunny with isolated showers. Highs around 89 near the shore to around 77 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 71 to 76 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Thursday: Sunny. Highs around 89 near the shore to around 77 above 3000 feet. Northeast winds up to 15 mph shifting to the southwest in the afternoon.

South Kaua’i

Today: Partly sunny with scattered showers. Highs around 86. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 69 to 75. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

Thursday: Sunny and breezy. Isolated showers in the morning. Highs around 86. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs 76 to 83 in the valleys to around 67 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 67 in the valleys to around 57 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Thursday: Mostly sunny with isolated showers. Highs 76 to 83 in the valleys to around 67 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 79 to 88. Southeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 65 to 75. Southeast winds up to 10 mph. Chance of rain 50 percent.

Thursday: Mostly sunny with isolated showers. Highs 79 to 88. East winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 20 percent.

East Kaua’i

Today: Partly sunny with scattered showers. Highs 79 to 87. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 63 to 76. Northeast winds up to 10 mph. Chance of rain 50 percent.

Thursday: Mostly sunny with isolated showers. Highs 79 to 87. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A high pressure system far north of the Hawaiian Islands will continue to produce moderate to locally breezy trade winds through Thursday, and then trade winds decrease in strength from Thursday night through the weekend. Passing showers will develop mainly along windward and mountain slopes in the early morning hours today and tonight near Kauai, as a weak low level trough moves westward through the islands. Drying trends are forecast from tonight through Friday, and then back to passing overnight showers by this weekend. Deeper tropical moisture may increase shower trends from late Sunday through Tuesday, as a remnant trough associated with former tropical cyclone Fernanda moves westward through the Hawaii region.

Discussion

The satellite water vapor imagery this morning continues to show a narrow upper trough just northwest of the state with two embedded upper lows, and more stable conditions moving into the islands from the east just as Tropical Storm Greg begins to pass south of the region. Infra-red satellite imagery shows a weak low level trough bringing clouds into the windward and mountain slopes from the Big Island to Oahu this morning, expect a slight increase in shower activity through the morning hours. Local radar imagery is detecting scattered showers for all windward areas this morning except for Kauai. Kauai will see shower activity pick up around sunrise this morning.
The high pressure ridge far north of the state will continue to produce moderate to locally breezy trade winds through Thursday. An upper level low will deepen north of the Hawaii region from Thursday night into the weekend, a surface trough will form under this upper low weakening the ridge. Trade wind speeds will weaken from Thursday night through the weekend, allowing local scale land and sea breezes to expand a bit over the terrain sheltered leeward slopes of each island during this time period. Tropical Storm Greg will pass far south of the Hawaiian Islands from later today through Thursday with no significant wind or weather impacts to the state.
Passing showers will continue through the morning hours as a weak low level trough passes through the state. Drying trends are forecast from tonight through Friday as a low level ridge shown on streamlines at 700 mb produces more stable conditions, lowering the trade wind temperature inversion height to around the 5,000 feet elevation level. Passing showers return just in time for the weekend, favoring windward and mountain areas in the overnight to early morning hours.
Deeper tropical moisture with increasing shower trends may develop by next week Sunday through Tuesday as a trough associated with the remnants of former tropical cyclone Fernanda move through the region. Expect warm humid weather conditions spreading from east to west across the state on Sunday with enhanced rainfall affecting most islands by Monday and Tuesday. Stay tuned for updates to the extended forecast as this weather pattern evolves over time.

Aviation

Surface high pressure north of the islands will allow moderate to locally breezy trades to persist through the forecast period. This pattern will bring scattered showers to the windward coasts and slopes with isolated showers elsewhere. There may be brief periods of MVFR ceilings and visibility associated with this activity, but not expecting anything widespread.
AIRMET TANGO for tempo moderate turbulence may be needed this afternoon for areas in the lee of mountains as winds increase slightly.

Marine

High pressure to the distant north and Tropical Storm Greg passing by well to the south will keep moderate to strong trades in place through Thursday. As a result, a Small Craft Advisory remains in effect for the typically windy waters around Maui and the Big Island through Thursday. The trades will ease to moderate levels Friday through early Sunday, then pick back up to locally strong levels late Sunday into early next week as the remnant low or trough of Fernanda slides by to the south of the island chain.
A series of small reinforcing northwest swells will keep north shore surf up above typical summertime flat levels through the remainder of the work week. North and west shore surf will return to flat levels Saturday through early next week.
South shore surf will remain small and below the summertime average through the weekend, with mainly background southerly swells. A small south swell may boost south shore surf up close to the summertime average early next week.
East shore surf will remain below normal levels through the next 7 days due to lack of strong trades upstream of the island chain.

HFO Watches/Warnings/Advisories

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