West Kaua’i

Rest Of Tonight: Mostly clear. Lows around 67 near the shore to around 57 above 3000 feet. North winds up to 10 mph in the evening becoming light.

Wednesday: Sunny. Highs 80 to 85 near the shore to around 74 above 3000 feet. Southwest winds up to 10 mph.

Wednesday Night: Mostly clear. Lows around 67 near the shore to around 58 above 3000 feet. Light winds.

South Kaua’i

Rest Of Tonight: Mostly clear. Lows around 68. North winds up to 10 mph in the evening becoming light.

Wednesday: Sunny. Highs 75 to 85. East winds up to 10 mph.

Wednesday Night: Clear. Lows 66 to 71. Northeast winds up to 10 mph.

Kaua’i Mountains

Rest Of Tonight: Partly cloudy with isolated showers. Lows 59 to 66 in the valleys to around 56 above 4000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers. Highs 73 to 80 in the valleys to around 66 above 4000 feet. Light winds. Chance of rain 20 percent.

Wednesday Night: Partly cloudy with isolated showers. Lows 60 to 66 in the valleys to around 56 above 4000 feet. Light winds. Chance of rain 20 percent.

North Kaua’i

Rest Of Tonight: Partly cloudy with isolated showers. Lows 61 to 70. Light winds. Chance of rain 20 percent.

Wednesday: Sunny. Isolated showers in the afternoon. Highs 74 to 82. North winds up to 10 mph. Chance of rain 20 percent.

Wednesday Night: Mostly clear with isolated showers. Lows 62 to 70. East winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Rest Of Tonight: Mostly clear with isolated showers. Lows 61 to 71. Light winds. Chance of rain 20 percent.

Wednesday: Sunny. Isolated showers in the afternoon. Highs 74 to 84. Northeast winds up to 10 mph. Chance of rain 20 percent.

Wednesday Night: Mostly clear. Isolated showers after midnight. Lows 62 to 72. North winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A land and sea breeze pattern will persist through Wednesday, leading to interior clouds and showers in the afternoon and evening and partial clearing at night. Trade winds will gradually return Thursday and Friday, and while rainfall will become focused over windward areas, a few afternoon showers will develop over leeward slopes. A slight increase in showers is possible for the weekend, followed by a stronger trade winds and more stable conditions early next week.

Discussion

Light winds and a somewhat stable land and sea breeze pattern is in place over the state. A broad low pressure passing far north of the islands has split the subtropical ridge and induced a weak surface trough north of Oahu. The resulting weak southeast to south winds over the region were easily overpowered by sea breezes today, leading to interior clouds and mainly isolated showers this afternoon. The exception was windward Oahu, where a fairly narrow band of showers that developed along the Koolau early this morning has helped to fuel scattered showers throughout the day. In spite of stable conditions and solid inversions between 6,000 to 7,000 feet on the afternoon soundings, a few of these showers have become briefly heavy. Away from windward Oahu, the main impact has been increased humidity as dew points climbed to around 70 degrees.
The humid land and sea breeze pattern will continue through Wednesday, with an uptick in shower activity expected along the surface trough as it meanders around the central portion of the island chain. As a result, expect decreased clouds and showers over most areas overnight and another round of afternoon clouds and isolated showers Wednesday afternoon. The weak lingering trough near Oahu and Molokai will lead to higher shower chances on these islands, where an isolated shower could occur through the night.
Kilauea eruption episode 46 started this morning and peaked midday. An Ashfall Advisory is in effect through the evening to highlight the possibility of tephra, ash, and Peles hair falling near the volcano. Due to relatively light winds veering with height, material from the eruption has been confined mainly just north and northeast of Kilauea.
Light to moderate trade winds will slowly rebuild Thursday and Friday as the subtropical ridge redevelops north of the state. Showers will become focused over windward slopes, though afternoon sea breezes will produce afternoon clouds and a few showers across sheltered leeward terrain. Dew points will drop back into the mid 60s and provide relief from the humidity.
An upper level trough passing overhead could generate an increase in showers during the weekend, but confidence remains rather low. Expect stronger trade winds and increased stability early next week.

Aviation

A light background wind pattern has allowed land and sea breezes to take place across most sites, and has also allowed clouds and showers to form over most island interiors. Some lingering showers embedded within the flow have also primarily impacted windward areas of Oahu and Maui. MVFR conditions are expected within showers, while VFR prevails elsewhere. Expect conditions to clear up overnight for island interiors, while windward areas over Oahu and Maui may still see lingering showers. Light winds are expected again tomorrow, along with afternoon clouds and showers over island interiors.
AIRMET Sierra is in effect for mountain obscurations for north through east sections of Oahu and Maui. No other AIRMET's are in effect.

Marine

A trough over the far northwest offshore waters will slowly track south through the islands, reaching the central waters Wednesday. This, combined with a larger synoptic scale low pressure system far to the north will lead to light and variable winds, with sea and land breezes present near the immediate coasts. A new high building northwest of the state will bring a return of light to moderate trades Thursday and Friday, with the trades strengthening to moderate and fresh levels over the weekend. Winds and seas are expected to remain below Small Craft Advisory thresholds through at least Friday.
A moderate medium-period northwest swell will gradually fade over the next couple of days. A new long period swell originating from a gale force low south of Kamchatka will build Wednesday night and give another boost to north and west shore surf Thursday and Friday. Surf will gradually decline over the weekend into early next week.
A series of overlapping south swells will keep intermittent small surf rolling into south facing shores during the next week. A small, long-period swell arriving Wednesday from a storm-force low that tracked southeast of New Zealand last week will likely provide a small bump in south shore surf through the end of the week.
Surf along east facing shores will remain below normal during the next 7 days due to the lack of strong trades over and upstream of the islands.

HFO Watches/Warnings/Advisories

Ashfall Advisory until 8 PM HST this evening for Big Island Southeast, Big Island East.

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Data Courtesy of NOAA.gov