West Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 71 near the shore to around 61 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Sunday: Mostly sunny. Isolated showers in the morning. Highs 84 to 90 near the shore to around 77 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Sunday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 69 to 74 near the shore to around 62 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 70 to 75. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 80 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows around 73. Northeast winds around 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 64 to 69 in the valleys to around 58 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Sunday: Partly sunny. Numerous showers in the morning, then isolated showers in the afternoon. Highs 75 to 84 in the valleys to around 67 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 65 to 70 in the valleys to around 59 above 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 64 to 73. East winds up to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 87. East winds up to 15 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows 65 to 73. East winds up to 10 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 64 to 76. Northeast winds up to 10 mph. Chance of rain 50 percent.

Sunday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 74 to 86. East winds up to 10 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows 64 to 76. East winds around 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will persist this afternoon, then weaken and veer out of the east-southeast late tomorrow into early next week as a broad, weak trough develops and moves across the area. The lighter flow may allow for some isolated sea breeze showers across leeward areas, in addition to the typical windward and mauka showers. Midweek and beyond, the high to our northeast will gradually build and bring breezy trades to the area by next weekend.

Discussion

High pressure systems far northwest and northeast of Hawaii will maintain moderate to locally breezy trade winds through this evening. This afternoon's radar and satellite imagery show some clouds and isolated showers moving into windward and mauka areas, along with clouds and showers building over the Kona slopes of the Big Island due to daytime heating.
A broad low level trough will develop over the islands tomorrow into Monday as an upper level trough digs in toward the northwestern end of the state. As a result, winds will weaken and veer east-southeasterly. The instability provided by this weak troughing near the state combined with pockets of moisture moving in on the trades may be enough to enhance windward and mauka showers during the overnight hours with some spillage over into interior and leeward areas, and to help some clouds and showers build over island interiors and leeward areas in the afternoons, where any sea breezes manage to develop in the lighter flow. More widespread sea breeze activity is expected Monday and Tuesday afternoons, when the trade winds are expected to be at their lightest. While the upper trough near the state may contribute to some shower enhancement before the surface trough and associated moisture clears the islands to the west Monday night, mid level ridging will still be present over the majority of the state…so not expecting a major uptick in shower activity as the weak surface trough moves across from the east.
By midweek, the low level flow will back out of the east and strengthen to moderate to locally breezy levels, with pockets of moisture riding in on the trades. Heading into next weekend, the surface high to our northeast will gradually build, strengthening the local pressure gradient and bringing breezy easterly trades across the island chain. Overall, typical trade wind weather can be expected through the second half of the week with periods of windward and mauka showers.

Aviation

Moderate to breezy trade winds will persist through tomorrow afternoon and start to weaken tomorrow evening. Passing showers will focus primarily over usual windward and mountain areas and be a little more intense during the night time/early morning hours. Brief periods of MVFR conditions will remain possible with any showers but overall VFR conditions should prevail.
AIRMET Tango remains in effect for low-level lee turb.

Marine

Moderate to locally breezy trades are expected to persist through tonight then gradually decrease Sunday into Monday as the ridge to our north weakens due to a pair of troughs developing far north and northwest of the state. The Small Craft Advisory (SCA) remains in effect for the typical windier waters and channels around Maui and the Big Island through tonight. Sunday will be a borderline SCA day with winds near the SCA threshold and we may see the SCA extended into Sunday. Early next week, with the pair of troughs far to our north and northwest, trade winds should veer slightly toward the east-southeast and weaken to gentle to moderate speeds. Moderate to fresh trades could return as early as Tuesday as the troughs move away from the area and a high builds far north of the state.
Surf along south facing shores should see a small, long-period south swell slowly fill in Sunday into Monday with surf peaking near or slightly above the summertime average on Monday or Tuesday. This swell will then gradually decline through the rest of next week.
Surf along east shores will gradually decline over the next several days due to the trade winds weakening. Surf along north facing shores will remain tiny throughout next week.

HFO Watches/Warnings/Advisories

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

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