West Kaua’i

Today: 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.

Tonight: Partly cloudy. Lows around 74 near the shore to around 64 above 3000 feet. Light winds.

Thursday: Mostly sunny. Highs 87 to 93 near the shore to around 80 above 3000 feet. East winds up to 15 mph.

South Kaua’i

Today: 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.

Tonight: Partly cloudy. Lows around 75. Northeast winds up to 10 mph.

Thursday: Mostly sunny with isolated showers. Highs 83 to 91. East winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: 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.

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

Thursday: Mostly sunny with isolated showers. Highs 78 to 87 in the valleys to around 71 above 4000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

North Kaua’i

Today: 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.

Tonight: Partly cloudy with isolated showers. Lows 68 to 76. East winds up to 10 mph. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Highs 80 to 89. East winds up to 15 mph. Chance of rain 20 percent.

East Kaua’i

Today: 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.

Tonight: Mostly cloudy. Lows 67 to 78. Northeast winds up to 10 mph.

Thursday: Partly sunny with scattered showers. Highs 76 to 89. East winds 10 to 15 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

The high pressure ridge north of the islands will remain fairly weak over the next several days, decreasing trade wind speeds especially as the remnants of former Tropical Cyclone Gil drifts westward, passing just north of the Hawaiian Islands through Thursday. Warm and very humid conditions are expected with an increase in island shower activity that will accompany Gil's passage. Tropical Cyclone Henriette will also drift westward, passing just north of the islands. This next system will produce similar lighter hybrid sea breeze and trade wind weather, along with very warm and humid conditions from Sunday through Monday.

Discussion

The satellite imagery this morning shows the remnants of former Tropical Cyclone Gil passing westward, just north of the Big Island. Some high level cirrus clouds, made of ice crystals, are drifting into the islands from the southwest direction. A few showers are moving into the islands as shown on local radar imagery. The subsidence temperature inversion height hovers around the 5,000 foot elevation level based on this mornings 2 AM HST (12Z) Upper Air sounding at Lihue. These inversion heights will rise from east to west across the state today into the 8,000 to 9,000 foot range as the deeper tropical moisture moves into the region.
In this hybrid sea breeze light trade wind pattern island mountain and interior sections will see more afternoon cloud and shower development. High boundary layer moisture levels with surface dew point temperatures in the low 70s and temperature inversion heights ranging from 8,000 to 9,000 feet will aid in convective heating driven shower development each afternoon through Thursday. Any of these developing slow moving showers could produce brief locally heavy shower activity in some leeward areas, particularly along the Kona slopes of the Big Island as low level moisture mixes up the mountain slopes.
Drier conditions return briefly with moderate trade winds on Friday and Saturday. Long range global models and National Hurricane Center forecasts show another tropical system, currently Tropical Storm Henriette, passing just north of the islands from Sunday through Monday, once again disrupting trade winds and producing warm and very humid weather. Moderate trade winds with drier trends develop by next week Tuesday and Wednesday.

Aviation

A hybrid sea breeze and light to moderate trade wind weather pattern remains in the forecast through Thursday as the remnants of former Tropical Cyclone Gil drifts westward, passing through the region just north of the Hawaiian Islands. Deep tropical moisture will sweep into the islands with this system, producing warm and very humid weather conditions with a slight increase in clouds and shower activity each afternoon over island mountain and interior sections.
No AIRMETs in effect. AIRMET Sierra for mountain obscurations will be possible each afternoon through Thursday.

Marine

Trade winds will be weakened and disrupted today with the passage of the remnants of what was once Tropical Cyclone Gil. This weak trough in the proximity of the northern offshore waters will create a period of light easterlies or variable breezes during its passage to the west. Trades will strengthen and become more easterly Thursday as this trough moves northwest of Kauai. Locally strong trades over the notoriously windier waters surrounding Maui and Big Island may prompt a Small Craft Advisory Thursday and Friday. High pressure far northeast of the state will drift to the north over the weekend as Tropical Storm Henriette approaches the region from the east. This may again disrupt and weaken trade flow once again as Henriette takes nearly the same path as Gil. Henriette will be near or north of the far northern Hawaiian offshore waters Sunday.
An extended run of higher south swell will continue through the week. Yesterday's south swell will continue to slowly decline through the day but long period forerunners from the next south swell will build in tonight. This swell will fill in Thursday and peak Friday morning and afternoon. A large reinforcing southern impulse will build in from late Friday through early Saturday. This swell will certainly lift south-facing surf to High Surf Advisory levels…possibly nearing High Surf Warning heights this weekend. This swell will gradually decline early next week.
Eastern exposure surf will be elevated through the day in response from a fading captured fetch from Tropical Cyclone Gil. Weakened winds has allowed the eastern swell to level out in the 3 to 4 foot / 12 second period range. Thus, under a much lighter wind regime, eastern surf will remain just under advisory heights today. East swell will decline rapidly late today and Thursday as strengthening trades regenerate near seasonal wind wave averages. A captured east swell from Tropical Storm Henriette may arrive this weekend.
A very small northwest swell originating from a former West Pacific typhoon is producing very small surf along north-facing shores. Another tiny northwest swell is scheduled to arrive later today into Thursday and this will prevent north surf from going completely flat.

Fire weather

Humidity levels will increase dramatically through Thursday as a tide of tropical moisture sweeps into the islands with the remnants of former Tropical Cyclone Gil passing by just north of the Hawaiian Islands. Another round of deep tropical moisture will sweep through the islands from Sunday into Monday as Henriette follows a similar path. Temperature inversion heights today near Maui and the Big Island will rise into the 8,000 to 9,000 foot range.

HFO Watches/Warnings/Advisories

None.