West Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Lows 71 to 76 near the shore to around 63 above 3000 feet. East winds up to 15 mph.

Tuesday: Mostly sunny with isolated showers. Highs 86 to 92 near the shore to around 78 above 3000 feet. East winds up to 15 mph shifting to the southwest in the afternoon. Chance of rain 20 percent.

Tuesday Night: Mostly cloudy. Lows around 73 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph.

South Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Highs 82 to 91. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday Night: Mostly cloudy with isolated showers. Lows 71 to 76. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 66 to 71 in the valleys to around 60 above 4000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 76 to 85 in the valleys to around 69 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tuesday Night: Breezy. Mostly cloudy with isolated showers. Lows 65 to 71 in the valleys to around 60 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

North Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 67 to 75. East winds up to 15 mph. Chance of rain 30 percent.

Tuesday: Mostly sunny with isolated showers. Highs 78 to 88. East winds up to 15 mph. Chance of rain 20 percent.

Tuesday Night: Mostly cloudy. Isolated showers in the evening. Lows 66 to 75. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 66 to 78. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs 75 to 88. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday Night: Mostly cloudy with isolated showers. Lows 65 to 77. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Trade winds will weaken to land and sea breezes by Wednesday as remnant of former Tropical Cyclone Gil passes just north of the state Wednesday and Wednesday night. Humidity, cloud cover and showers will increase Tuesday night through Thursday.

Discussion

A distant 1025 mb high to the northeast will drive trade winds through Tuesday, but will come under less influence as the remnants of former Tropical Cyclone Gil approach Hawaii. Gil is currently a swirl of low clouds about 800 miles east of Hilo this afternoon, and is expected to open to a surface trough as it passes just north of the state Wednesday and Wednesday night. However, the low/trough will pass in between the driving subtropical high and weaken the winds down to where nighttime land breezes and daytime sea breezes dominate.
Gil remnants will bring cloud cover and very humid air mass across the state. While most of the trough of what is left of Gil will pass to the north, some of the clouds and showers along the southern fringes will impact the islands from Tuesday night through Thursday. Clouds and showers will focus windward at night through this period as land breezes will suppress this across leeward sides of the islands. Sea breezes will bring scattered interior clouds and showers, some moderate-heavy intensity at times.
Drier conditions return briefly with moderate trade winds on Friday and Saturday. Long range global models currently show another weakening tropical system, currently Tropical Storm Henriette in the East Pacific, will pass north of the islands from Sunday through Monday, once again disrupting trade winds and producing warm and very humid weather. Stay tuned for weather forecast updates as the track of this next approaching tropical system will likely change over time.

Aviation

Moderate to locally breezy trade winds will gradually decrease into the light to moderate range tonight into tomorrow. Clouds and showers will primarily focus over windward and mountain areas, and remain fairly light and brief due to the stable atmospheric profile. Overall VFR conditions are expected.
Remnant moisture associated with former tropical cyclone Gil will pass just north of the islands on Wednesday, increasing cloud and shower coverage.
AIRMET Tango remains in effect for moderate low level turbulence over and immediately south through west of island mountains. This AIRMET will likely be cancelled later today as wind speeds aloft decrease.

Marine

High pressure north of the state will weaken and drift eastward through tomorrow. Trades will gradually lower through the middle of the week as the remnants of former Tropical Cyclone Gil pass to the northeast of the state, then strengthen out of the east southeast late Thursday through Friday. The Small Craft Advisory (SCA) is in effect for the windier waters and channels around Maui County and the Big Island through 6 AM.
A moderate, long period south swell that is filling in now should peak near High Surf Advisory (HSA) criteria this evening into Tuesday before declining Wednesday. Another swell is expected from a low that formed last week south of New Zealand. This swell is expected to build in on Thursday and hold through the weekend which could peak near HSA criteria.
Short period trade wind swell will keep east facing shores elevated and choppy due to strong trades. Late this evening into Tuesday, a moderate, medium to long period east swell is expected to fill in from the remnants of Tropical Cyclone Gil and may also peak near HSA criteria.
A small, medium period northwest swell originating from former Typhoon Krosa in the western Pacific is bumping the surf up a bit along north facing shores. Another bump is expected Thursday and Friday as a small, medium to long period northwest swell looks to fill in.

Fire weather

Humidity levels will increase while winds speeds decrease through Wednesday. Inversion heights will be around 5000 to 6000 feet with very low relative humidity values at and above this elevation. Humidity levels will increase dramatically from Tuesday night through Thursday as the remnants of former Tropical Cyclone Gil pass just north of the Hawaiian Islands and block the trade wind flow.

HFO Watches/Warnings/Advisories

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

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