West Kaua’i

Rest Of Tonight: Partly cloudy with isolated showers. Lows 72 to 77 near the shore to around 64 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Sunny and breezy. Highs 87 to 93 near the shore to around 79 above 3000 feet. East winds up to 20 mph.

Wednesday Night: Partly cloudy in the evening then becoming mostly cloudy. Lows 72 to 77 near the shore to around 64 above 3000 feet. East winds up to 15 mph.

South Kaua’i

Rest Of Tonight: Mostly cloudy with scattered showers. Lows around 75. East winds 10 to 15 mph. Chance of rain 40 percent.

Wednesday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 82 to 91. East winds 10 to 20 mph. Chance of rain 40 percent.

Wednesday Night: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 73 to 78. East winds 10 to 20 mph. Chance of rain 30 percent.

Kaua’i Mountains

Rest Of Tonight: Mostly cloudy with scattered showers. Lows 67 to 72 in the valleys to around 61 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Mostly sunny with scattered showers. Highs 77 to 86 in the valleys to around 68 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday Night: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows 67 to 72 in the valleys to around 61 above 4000 feet. East winds up to 20 mph increasing to 10 to 25 mph after midnight. Chance of rain 40 percent.

North Kaua’i

Rest Of Tonight: Mostly cloudy with scattered showers. Lows 67 to 76. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 79 to 89. Southeast winds up to 15 mph. Chance of rain 30 percent.

Wednesday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 67 to 76. East winds up to 15 mph. Chance of rain 20 percent.

East Kaua’i

Rest Of Tonight: Mostly cloudy with scattered showers. Lows 67 to 78. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers. Highs 75 to 88. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 67 to 79. East winds 10 to 15 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Light to moderate trades will strengthen over the next couple of days to moderate to locally strong as a high north of the state builds. Clouds and showers will focus along windward and mauka areas, particularly overnight and early morning as a rather dry and stable airmass settles over the state and persists into next weekend.

Discussion

Residing equatorward of the upper jet draped roughly along 30N, the islands are under the influence of modest mid-level subsidence and surface high pressure established over the NE Pacific Basin. Expect nothing more than periodic batches of showers focused windward and mauka, mainly overnight and during the early morning period amounting to little overall rainfall through the forecast period. The surface pressure gradient with strengthen over the next few days from the high to our northeast and tropical cyclones passing far south of Hawaii, yielding breezy to locally strong trades. This potentially results in a few more light showers penetrating leeward overnight.

Aviation

Trade winds will increase over the next few days. Low clouds and showers will mainly focus over windward and mauka locations. MVFR conditions are possible in SHRA. Otherwise VFR will prevail.

Marine

Moderate to strong trade winds will be in place through the weekend as high pressure builds north of the area. The current Small Craft Advisory (SCA) remains in effect for the typical windy waters and channels around Maui County and the Big Island and will expand in coverage to include the Kauai waters tomorrow morning as trade winds strengthen. This SCA will likely continue through the weekend.
The two current tropical cyclones in the Central Pacific are forecast to pass several hundred miles south of Hawaii over the next couple of days, more information on Hurricane Iona can be found at WMO header WTPA21 PHFO and AWIPS header HFOTCMCP1, and information on Tropical Storm Keli can be found at WMO header WTPA22 PHFO and AWIPS header HFOTCMCP2. Additional Tropical Cyclone development is expected far southeast of Hawaii in the next few days. Isolated thunderstorms along the northern periphery of these systems may effect the far southern portion of the offshore waters, and while some short- period southeast swells may reach southern and southeastern shores of Hawaii, a much larger and unrelated south swell will dominate.
A multi-day buildup of surf for south facing shores is expected this week as a series of long period swells fill in. The first swell is forecast to arrive later today into tonight and peak near the summertime average tomorrow (5-6 ft). While that swell holds tomorrow, forerunners from the next much larger well will start to fill in and peak late Thursday at well over advisory levels (8 to 12 ft) and hold through Friday. The swell will gradually decline over the weekend and will be followed by another long period south swell early next week.
East shore surf will trend up over the next few days as strengthening trade winds generate larger wind waves. Surf along east facing shores will rise to seasonal average late Wednesday or Thursday and hold into the weekend, followed by a possible decline early next week.
Flat summer conditions along north facing shores may be interrupted this weekend by a small long period northwest swell from Typhoon Krosa, currently in the western Pacific.

Fire weather

Expect humidity levels to gradually lower to more typical summertime levels through today as a drier and more stable airmass builds over the state. Humidity and wind speeds will be near critical conditions Wednesday into the weekend as breezy conditions develop. Some uncertainty remains in the wind speeds later this week and will continue to monitor for possibility of any headlines.

HFO Watches/Warnings/Advisories

Tsunami Warning for the state of Hawaii and for all Hawaiian waters.
Small Craft Advisory from 6 AM Wednesday to 6 AM HST Thursday for Kauai Northwest Waters, Kauai Leeward Waters.
Small Craft Advisory until 6 AM HST Thursday for Kaiwi Channel, Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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