West Kaua’i

Tonight: Mostly cloudy in the evening then becoming mostly clear. Lows 70 to 75 near the shore to around 62 above 3000 feet. North winds up to 15 mph shifting to the northeast after midnight.

Wednesday: Mostly sunny early in the morning, then scattered showers in the late morning and afternoon. Highs 86 to 93 near the shore to around 79 above 3000 feet. North winds up to 10 mph shifting to the southwest in the afternoon. Chance of rain 40 percent.

Wednesday Night: Partly cloudy in the evening then becoming mostly cloudy. Lows around 74 near the shore to around 64 above 3000 feet. Light winds.

South Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 84 to 92. Northeast winds 10 to 15 mph shifting to the southeast in the afternoon. Chance of rain 40 percent.

Wednesday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows around 75. Northeast winds up to 10 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Isolated showers. Lows 65 to 70 in the valleys to around 60 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 77 to 86 in the valleys to around 70 above 4000 feet. East winds 10 to 15 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy. Lows 67 to 72 in the valleys to around 62 above 4000 feet. East winds up to 15 mph.

North Kaua’i

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 66 to 74. East winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny. Isolated showers in the late morning and afternoon. Highs 79 to 88. East winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 20 percent.

Wednesday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 68 to 76. East winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 65 to 77. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers early in the morning, then mostly sunny with scattered showers in the late morning and afternoon. Highs 78 to 90. Northeast winds around 10 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy with isolated showers. Lows 67 to 78. Northeast winds up to 10 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 through Wednesday night. Humidity, cloud cover and showers will increase through Thursday, and will repeat Sunday through Monday as Henriette passes to the north.

Discussion

Former Tropical Cyclone Gil, currently centered 430 miles northeast of Hilo, will open to a trough as it passes north of state on Wednesday. Winds will weaken this evening to where nighttime land breezes and daytime sea breezes dominate through the following 24 hours.
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, moisture along the southern fringes will get caught in Wednesday's sea breeze flow and allow for interior clouds with scattered showers to set up for all islands in the afternoon. Some showers could become briefly moderate-heavy intensity. The trough will move west of the area Wednesday night with some lingering clouds and showers expected around the area Thursday.
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 with land and sea breezes, along with warm and very humid conditions.

Aviation

Light to moderate trade winds today will diminish further tonight into tomorrow morning as a trough drifts just north of the area. Land and sea breezes can be expected tomorrow and an influx of moisture from the trough could allow for increased cloud and shower coverage. Due to the nature of the sea breezes, the highest cloud and shower chances look to come tomorrow afternoon for interior and leeward areas as well as the slopes of the Big Island. VFR conditions will be most prevalent with MVFR conditions in the showers.
No AIRMETs in effect and none are expected until tomorrow where AIRMET Sierra for mountain obscurations will be possible.

Marine

Moderate to fresh northeasterly trade winds will weaken tonight and Wednesday as a surface trough passes north of the islands. Trade winds will strengthen and become more easterly on Thursday as the trough moves northwest of Kauai, and a Small Craft Advisory (SCA) will likely be needed for the typically windy waters near Maui County and the Big Island Thursday and Friday. High pressure far northeast of the state will drift to the north over the weekend as Tropical Storm Henriette nears the region from the east, and local winds are expected to decline below SCA strength by Saturday. Henriette will be near or north of the islands by Sunday.
An extended run of south swell will continue this week. During its peak last night and this morning, the current swell produced surf at the High Surf Advisory (HSA) threshold, and this swell will continue to slowly decline through Wednesday. Long-period forerunners from the next south-southwest swell will build late Wednesday, and during the Thursday peak of the swell, south shore surf should remain below the HSA threshold. A larger south swell will build Friday through Saturday, generating surf well above the HSA threshold, and possibly near the High Surf Warning level, into Sunday. This swell will gradually decline early next week.
Even as wind wave energy declines with the easing trades, east shore surf will be elevated through Wednesday due to east swell produced by former Tropical Cyclone Gil. Windward PacIOOS buoys have been registering swell of around 3 feet at 13 seconds today, and guidance suggests that the swell may rise as high as 5 or 6 feet tonight as the period drops to 11 or 12 seconds. This may be enough energy to produce HSA level surf along east facing shores into Wednesday morning. Due to a lack of confidence in the rising swell, we have opted to hold off on issuing a HSA for now but will monitor the buoys tonight. The swell will decline rapidly late Wednesday and Thursday as strengthening trades generate near seasonal average wind waves. As waves decline over the weekend, east swell from East Pacific Tropical Storm Henriette may arrive.
A very small northwest swell originating from a former West Pacific typhoon is producing tiny surf along north shores. Another tiny northwest swell is scheduled to arrive late Wednesday into Thursday, preventing north shore surf from going completely flat.

Fire weather

Trades will diminish tonight while humidity levels increase as a tide of tropical moisture sweeps into the islands as the remnants of former Tropical Cyclone Gil drifts westward and passes just north of the Hawaiian Islands on Wednesday. Another round of deep tropical moisture will sweep through the islands from Sunday into Monday as Henriette follows a similar path.

HFO Watches/Warnings/Advisories

None.