West Kaua’i

Tonight: Mostly clear with isolated showers. Lows around 72 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 20 percent.

Thursday: Sunny with isolated showers. Highs 85 to 91 near the shore to around 77 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Thursday Night: Mostly clear with isolated showers. Lows 70 to 75 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph becoming around 10 mph after midnight. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 82 to 89. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with scattered showers. Lows 64 to 70 in the valleys to around 59 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Thursday: Partly sunny with scattered showers. Highs 74 to 83 in the valleys to around 67 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows 64 to 70 in the valleys to around 60 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy with scattered showers. Lows 65 to 74. East winds around 10 mph. Chance of rain 50 percent.

Thursday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 88. East winds up to 15 mph. Chance of rain 40 percent.

Thursday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 65 to 74. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 65 to 77. Northeast winds around 10 mph. Chance of rain 50 percent.

Thursday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 74 to 86. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows 65 to 77. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Partly cloudy conditions with scattered showers and moderate trades continue through Friday night. Surface winds will weaken Saturday in advance of an approaching boundary (the remnants of a cold front) that will be pushed south into the western islands late this weekend. This will bring wetter and cloudier weather Sunday through Tuesday or Wednesday.

Discussion

This afternoon, radar shows scattered showers, some strong, over the Kona region of the Big Island. A band of enhanced low level moisture was responsible for these showers, and we expected this band to move west of the Big Island tonight. This band may clip the eastern and southern part of Maui County through this evening. Otherwise, only isolated windward showers were occurring on the remaining islands as of 3 PM HST.
Currently, upper level ridges to our NW and NE have left a trough over the state. This has resulted in an unstable atmosphere and the possibility of strong showers and perhaps a thunderstorm over the Kona region on the Big Island. Other areas will see isolated to scattered showers driven by the trade winds, favoring windward sides as usual. This same pattern will be with us again Thursday. Conditions will become more stable Friday as cold air aloft associated with the upper trough moves away to the east.
The remnants of a cold front will move south toward the state this weekend, likely moving into western islands Sunday morning. Surface winds will weaken late Saturday as the boundary draws near. Precipitation chances will increase as moisture convergence increases on both sides of the boundary. It is currently forecast to stall out somewhere over the state, with odds slightly favoring the western half, but models have a difficult time with these features and confidence in how far east it will go is low. Specifics are not required to note that this general pattern should result in a continued increase in showers into early next week over the entire area, and the forecast has been trended farther in that direction.

Aviation

Moderate trade winds will persist during the next few days as a surface ridge holds north of the state, and a sharp upper-level trough will linger over the islands, maintaining some instability and producing periods of turbulence aloft.
A pocket of moisture moving along the trade wind flow has produced extensive MVFR cloud cover and reduced visibility in SHRA across windward Big Island through much of the day and has generated heavy showers along leeward slopes and some interior sections this afternoon. AIRMET Sierra for mountain obscuration is in effect for much of the Big Island through the afternoon hours and may need to be extended into the evening. As drier air moves in on the trades and leeward showers diminish, the AIRMET should dropped by midnight. Away from the Big Island, VFR will dominate, with only isolated MVFR conditions over windward areas.
The upper-level trough will likely produce moderate turbulence over the western end of the island chain into Thursday. AIRMET Tango is currently in effect over and around Kauai from FL220 to FL360. This AIRMET will likely be extended through the evening with a possible expansion to Oahu.

Marine

Weak high pressure anchored north of the Hawaiian Islands will maintain moderate to locally fresh trades into the weekend. The potential then exists for trades to back to a more NEly direction and become strong over the western waters in the wake of a cold front that is forecast to advance through part or all of the island chain Sunday into early next week. A Small Craft Advisory for winds and/or seas may be needed for portions of the area during this time.
Short period NNW (330-350) swell has filled in and is likely near its peak this afternoon. This swell will fade during Thursday. A small, long period NNW swell (330) will fill in Thursday night and peak Friday, keeping surf along N and W shores elevated. Surf will then trend sharply upward late Friday through Monday in response to a couple of swells sent toward the islands by an active pattern across the N Pac. Forerunners of the first moderate, long period NNW (330) swell will arrive late Friday with swell peaking Saturday near or below the High Surf Advisory (HSA) threshold. The next small to moderate, medium period NNW (340) swell will arrive quickly late Saturday. This swell will likely peak above the HSA threshold. Messy forecast scenario unfolds during this time as model swells seem to be contaminated by emerging strong NNE post- frontal wind swell leading to a larger and more N swell in the output than expected. However, even a conservative approach suggests HSA- criteria surf for N and W facing shores for the Sunday-Monday period.
Surf along E shores will remain small to moderate through the week. Strengthening post-frontal NNE trades may bring a rapid increase in wind waves and short period fresh swell for favored exposures early next week, particularly over the western end of the state. South facing shores will see a slight boost in surf today as a small, long period south swell fills in before slowly fading Thursday through the rest of the week.

Fire weather

Winds and relative humidity will not meet fire weather thresholds over the next few days. With additional moisture forecast for the weekend, it is unlikely we will see dangerous fire weather through the next week or so.

HFO Watches/Warnings/Advisories

None.

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