West Kaua’i

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 86 to 91 near the shore to around 76 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 70 to 75 near the shore to around 62 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Thursday: Mostly sunny with isolated showers. Highs 86 to 91 near the shore to around 78 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 81 to 90. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 82 to 90. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 84 in the valleys to around 66 above 4000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 64 to 70 in the valleys to around 59 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Thursday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 84 in the valleys to around 67 above 4000 feet. East winds 10 to 20 mph. Chance of rain 60 percent.

North Kaua’i

Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 77 to 89. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 74. East winds up to 15 mph. Chance of rain 70 percent.

Thursday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 78 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 86. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 66 to 77. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Thursday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 75 to 86. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to breezy trade winds will become breezy to locally windy Friday into the weekend as the high pressure to the north of the state strengthens. Showers will move into windward and mauka areas, and occasionally spill over to interior and leeward sides. Pockets of drier air filtering across the region Thursday and Friday, coincident with the stronger winds, will begin to elevate fire weather concerns. By early next week, trades will weaken slightly and rain chances will potentially increase, but forecast confidence decreases as model solutions diverge.

Discussion

Pockets of moisture riding in on the moderate to breezy trades are bringing numerous to scattered showers across the island chain early this morning. While showers are favoring windward and mauka areas, the proximity of an elongated upper level low east of the state is allowing inversion heights to remain elevated, enhancing shower development and allowing for showers to occasionally pass over island terrain into interior and leeward areas. This upper level low will also bring the potential for isolated thunderstorms to the higher elevations of Big Island, particularly on Thursday afternoon when models show the coolest temperatures aloft.
The surface high pressure to the northwest of the state that is driving the moderate to breezy trades today will gradually strengthen and slide eastward along 30N through the weekend. As it does so, the local pressure gradient will strengthen and thereby strengthen the trade winds. The trades are expected to be strongest Friday into Saturday, with some of the typically windier areas potentially flirting with Wind Advisory criteria (sustained wind speeds 30 mph). Pockets of moisture will continue to deliver showers to windward and mauka areas, particularly during the overnight to early morning hours, but models show a brief period of drier air filtering across the area during the day on Thursday, followed by a plume of moisture overnight, and another pocket of drier air Friday through the weekend. As the timing of the drier air and stronger wind speeds line up, fire weather concerns increase. See the Fire Weather section below for more details.
Model guidance is in decent agreement on showing that the upper level low will break free from its parent trough over the weekend and retrograde westward near to or over the island chain. However, guidance begins to diverge more significantly heading into early next week in regards to the progression of this upper level feature, decreasing forecast confidence. For now, going with a moderate to locally breezy trade wind pattern Sunday into early next week as the high pushes further to the east and weakens, with a slightly wetter trade wind pattern Monday into Tuesday to reflect the overall model trend.

Aviation

Moderate to breezy trades will gradually strengthen tomorrow as high pressure to the north strengthens. Clouds and showers will continue to move into windward and mountain areas with some limited spillover to leeward areas. MVFR conditions are possible in heavier showers, otherwise VFR should prevail.
AIRMET Tango is in effect for moderate turbulence below 9000 ft downwind of island terrain as well as between FL250 and FL350 for moderate turbulence aloft.
AIRMET Sierra is in effect for windward areas of Kauai through Maui as showers stream into these areas early this morning. Conditions should improve later this morning.

Marine

A high pressure ridge north of the Hawaiian Islands will continue to produce moderate to strong trade winds lasting into the weekend. The Small Craft Advisory (SCA) was extended in time through Friday morning for the typical windy waters around the Big Island and Maui County. This SCA will likely continue through the weekend. An expansion in SCA coverage may develop later this week as strong winds expand in area and seas approach 10 ft over additional coastal waters.
Two north-northwest (330-340 deg) swells, one medium period and one long period, are moving through the Hawaii region today. The long period swell will build surf heights through the day, peaking later tonight through Thursday near High Surf Advisory (HSA) thresholds for north and west facing shores, before slowly decreasing on Friday. Another long period north-northwest (330-340 deg) swell builds into the region on Friday, this next swell will also approach HSA thresholds along north and west facing shores from Friday night into Saturday.
Rough and choppy surf will continue along east facing shores due to strong trade winds with increasing trends from late Thursday into the weekend. Small background south swell energy will continue to keep surf along south facing shores above flat levels into early next week.

Fire weather

Batches of increased moisture filtering across the region and slight instability should keep conditions below critical fire weather thresholds today. By Thursday morning, increasing trade wind speeds and decreasing moisture will start increasing the potential for fire weather concerns. Model guidance shows an elevated risk for reaching critical fire weather thresholds on Friday due to the low moisture levels and strong trade winds. We will continue to monitor the fire weather risk as conditions evolve.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Friday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.