West Kaua’i

Rest Of Tonight: Mostly cloudy with isolated showers. Lows around 73 near the shore to around 63 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Partly sunny. Highs 84 to 90 near the shore to around 75 above 3000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon.

Friday Night: Partly cloudy. Isolated showers in the evening. Lows around 72 near the shore to around 63 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Rest Of Tonight: Mostly cloudy. Breezy. Scattered showers early in the evening, then isolated showers after midnight. Lows 69 to 76. Northeast winds 15 to 20 mph. Chance of rain 40 percent.

Friday: Breezy. Partly sunny with isolated showers. Highs 79 to 88. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Friday Night: Breezy. Partly cloudy with isolated showers. Lows 69 to 76. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Kaua’i Mountains

Rest Of Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 68 in the valleys to around 61 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Mostly cloudy with scattered showers. Highs 72 to 79 in the valleys to around 65 above 4000 feet. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 68 in the valleys to around 60 above 4000 feet. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Rest Of Tonight: Breezy. Mostly cloudy with scattered showers. Lows 64 to 74. East winds 10 to 20 mph. Chance of rain 40 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 68 to 84. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday Night: Breezy. Partly cloudy with isolated showers. Lows 64 to 74. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

East Kaua’i

Rest Of Tonight: Mostly cloudy with scattered showers. Lows 65 to 76. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 76 to 84. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 65 to 75. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Trade winds will increase in strength tonight into Saturday due to a tropical disturbance passing well to the south of the area and a strong high building in from the northwest. Enhanced trade wind showers are also anticipated for windward areas tonight into the weekend as tropical moisture surges in from the southeast.

Discussion

The 18Z surface analysis shows a ridge of high pressure north of the state driving breezy trades across the island chain this afternoon and a trough to the southeast of the Big Island. Radar imagery shows isolated light to moderate showers in windward areas. Also of interest is the plume of volcanic emissions growing from Kilauea's eruption today. Trade winds are pushing this plume west and any light ashfall will likely occur over the Kau District and Highway 11 west of the town of Volcano and possibly as far southwest as Pahala. For more information, please refer to the Special Weather Statement in effect.
The tropical disturbance southeast of the islands remains an elongated trough for the time being. The latest ASCAT pass from 1928Z indicates winds remain less than 25 kts north of 20N latitude, which is a reduction from the last couple passes. While some uptick in winds is likely near the typically favored terrain features this evening, confidence for a larger scale increase of wind has decreased. Therefore, held off on Wind Advisories for now.
Satellite derived pwats from CIMSS depicts deeper moisture approaching the Big Island from the southeast late this afternoon. By late tonight and Friday, pwats should exceed 2 inches across the Big Island. A sharp uptick in shower development is expected in windward and mauka areas, possibly leeward as well. Isolated thunderstorms capable of producing heavy downpours cannot be ruled out for Big Island through Friday as the deep moisture erodes inversion heights, allowing for some terrain induced convection to occur. Total rainfall totals of 2 to 3 inches appear likely for windward Big Island with some areas possibly approaching 4.
After the system passes west of the state Saturday into Sunday, a much drier airmass and lower inversion heights will filter in from the east into next week. Winds will ease to more typical levels. The drier airmass and lower inversion heights will also limit shower coverage to mainly windward areas.

Aviation

Breezy trades will continue for the next few days. An area of enhanced moisture moving in from the east will affect windward portions of the Big Island and to a lesser extent, the rest of the islands tonight into tomorrow morning, bringing more widespread MVFR with pockets of IFR for windward areas. Isolated showers with brief MVFR conditions could also spill over to leeward areas, mostly during the evening and early morning hours.
AIRMET Sierra is in effect for mtn obsc for windward portions of Kauai and Oahu due to persistent showers. Conds should become worse later tonight as more moisture moves in and the AIRMET could expand to include more islands.
AIRMET Tango remains in effect for mod turb lee of terrain and should remain in effect for next few days.

Marine

Fresh to strong trade winds with periods of near gales will prevail through the weekend as high pressure persists north of the state. A Small Craft Advisory (SCA) remains in place for all Hawaiian Waters for a combination of winds and elevated seas. The SCA was extended through Saturday night and will likely remain in place through at least Sunday night as a disturbance or tropical cyclone passing a couple hundred miles to the south keeps the local pressure gradient tight. Winds are expected to ease slightly as the ridge to our north erodes and the potential tropical cyclone moves away to the southwest. The SCA will likely be trimmed back to the typical windy waters around Big Island and Maui sometime Monday or Tuesday.
A long-period north-northwest (325 to 345 degree) swell will peak through evening and produce surf well above High Surf Advisory thresholds along exposed north and west facing shores from Kauai to Maui. Recent observations from NOAA buoy 51001 northwest of Kauai showed the swell at around 9 feet at 16 seconds, and swell energy at the PacIOOS Waimea buoy continues to slowly rise this afternoon. Surf will decline below advisory thresholds late Friday as the north-northwest swell declines. Reinforcing medium period energy out of the north-northwest (330 to 340 degree) should arrive late Saturday into Sunday. Surf could approach advisory thresholds during its peak early Sunday morning. Another large northwest to north-northwest swell is Wednesday or Thursday of next week.
A small south-southwest swell is expected to fill in overnight. This small bump should peak Friday with waves slightly above average for this time of year Friday into Saturday along south facing shores. Surf along east-facing shores will stay elevated and choppy through much of the week due to the strong trades. Select northeast exposures should see long-period energy from the large north-northwest swell today through tonight.

Fire weather

Persistent rainfall will continue to limit the widespread availability of receptive fuels. Breezy and gusty winds will continue during the next several days, generating moderate fire weather conditions. Isolated thunderstorms will be possible for Big Island tonight through Friday. The inversion near Big Island will range from 8000 to 10000 ft through Friday.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Friday for Kauai North, Kauai Southwest, Maui Central Valley North, Maui Windward West, Molokai North, Molokai West, Molokai Windward, Niihau, Oahu North Shore, Waianae Coast, Windward Haleakala.
Small Craft Advisory until 6 AM HST Sunday for Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters, Big Island Windward Waters, Kaiwi Channel, Kauai Channel, Kauai Leeward Waters, Kauai Northwest Waters, Kauai Windward Waters, Maalaea Bay, Maui County Leeward Waters, Maui County Windward Waters, Oahu Leeward Waters, Oahu Windward Waters, Pailolo Channel.

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Data Courtesy of NOAA.gov