Photo Credit: Sebastien Gabriel

West Kaua’i

Rest Of Today: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 89 near the shore to around 77 above 3000 feet. West winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 72 near the shore to around 62 above 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs around 88 near the shore to around 76 above 3000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

South Kaua’i

Rest Of Today: Mostly cloudy with scattered showers. Highs 81 to 87. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 72. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Mostly cloudy with scattered showers. Highs 80 to 85. East winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Rest Of Today: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 78 to 83 in the valleys to around 68 above 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Tonight: Cloudy with numerous showers. Lows around 68 in the valleys to around 58 above 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 70 percent.

Sunday: Mostly cloudy with numerous showers. Highs 77 to 82 in the valleys to around 67 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Rest Of Today: Mostly cloudy with scattered showers. Highs 79 to 89. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with numerous showers. Lows 65 to 74. East winds up to 10 mph. Chance of rain 70 percent.

Sunday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 78 to 88. East winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

East Kaua’i

Rest Of Today: Mostly cloudy with scattered showers. Highs 77 to 85. Northeast winds up to 15 mph shifting to the east in the afternoon. Chance of rain 50 percent.

Tonight: Cloudy with numerous showers. Lows 66 to 75. East winds up to 10 mph. Chance of rain 70 percent.

Sunday: Mostly cloudy with numerous showers. Highs 75 to 84. East winds around 10 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Light to moderate trades will persist through this evening. Periods of moderate to locally heavy rainfall will continue to spread northwestward across the island chain today and persist into tomorrow, with isolated thunderstorms possible over the eastern end of the state. Breezy trades with slightly drier conditions are expected next week.

Discussion

A dissipating stationary front just north of the state is helping to keep the local pressure gradient relatively weak, which will allow light to moderate trades to persist through this evening. A plume of deeper tropical moisture is expanding northwestward across the island chain this morning with moderate to occasionally heavy showers impacting portions of the Big Island through Oahu.
The plume of moisture will continue to expand northwestward across the island chain through the day today, while remnant moisture from the stationary front also sags south. The trades will likely be light enough to allow sea breeze convergence to tap into the increased low to mid level moisture this afternoon, bringing clouds and showers to leeward/interior areas across the island chain. These showers will be further enhanced by an upper level shortwave trough that will deepen to our north and begin to move overhead later today. Atmospheric instability will increase as this upper level feature moves closer and will maintain the possibility for deeper convection and isolated thunderstorms, particularly for the eastern end of the state. With all of these ingredients in play, any slow-moving heavy showers or thunderstorms will have the potential to cause nuisance type flooding on any of the islands today. However, it's worth noting that high clouds moving in from the north may put a damper on diurnal heating and hence the sea breeze development, but model guidance is suggesting that sea breezes and their resulting showers will likely form, so will continue to lean into that for this forecast package.
Trades will gradually strengthen to become locally breezy tomorrow as the front dissipates and ridging begins to build to the north. The upper level low will move more directly overhead providing increasingly unstable conditions aloft, and with plenty of low to mid level moisture still streaming across the state, it won't take much to kick off moderate to locally heavy showers. With the strengthening trades, showers will likely transition to focus mainly over windward areas as is typical in a wetter trade wind pattern. However, showers will also still form in the more sheltered leeward areas, including leeward and interior portions of Maui and the Big Island. Nuisance flooding will still be a concern for any slow-moving heavy showers, or for any heavy showers that anchor over any particular area.
As the upper low pushes west of the area and surface ridging builds to the north, a breezy and increasingly stable trade wind flow is expected to persist Monday through Friday. Pockets of moisture riding in on the trades will provide brief upticks in windward showers during this period.

Aviation

Light to moderate trades will continue through the weekend. Lighter winds across the western half of the state will allow for afternoon sea breezes with possible isol SHRA and low cigs over Oahu and Kauai. Slightly stronger winds expected over the eastern half of the state. A plume of moisture will continue moving across the state in conjunction with an upper level low expected to move overhead. Enhanced SHRA with the possibility of some isol TSRA is expected. Within any SHRA/RA/TSRA periods of IFR/MVFR conds are possible. VFR should prevail otherwise.
AIRMET Sierra for mtn obsc is in effect over windward Big Island and Maui. This will likely be needed through the weekend.

Marine

A frontal system to the north of the islands continues to maintain light to moderate winds over the area today. As the front continues weaken today, expect moderate to locally strong trades to build back in due to a ridge north of 30N. The trades should continue to strengthen into the first half of the new week with widespread strong trades possible by midweek. Small Craft Advisories for the typical windy waters around Maui County and the Big Island are possible late today, but more likely Sunday.
A mid to upper level disturbance to the northeast of the islands combined with abundant moisture moving over the region from the east, will continue the chance for thunderstorms in both the coastal and offshore waters. While the chance for thunderstorms over the coastal will diminish by Sunday, the offshore waters will have the chance into midweek.
The nearshore buoys exposed to the north-northeast swell peaked overnight, with the swell now on the decline. Surf along east facing shores is expected to fall below advisory levels by tonight. However, the combination of strengthening trades and a small long-period east swell from Tropical Cyclone Kristy should continue to produce rough and elevated surf along east facing shores throughout the new week. After a few days of strong trades, surf could build to advisory thresholds of 10 feet along east facing shores by the middle of next week. Another small to moderate north swell should fill in on Sunday and peak on Monday then gradually decline. A new long-period south swell is expected to peak today, and then slowly decline into the early part of the new week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Olomana, Maui Windward West, Kauai East, Koolau Windward, Molokai Southeast, Windward Haleakala, Big Island East, Big Island North.

Data Courtesy of NOAA.gov