West Kaua’i

Tonight: Mostly clear. Isolated showers after midnight. Lows 66 to 71 near the shore to around 59 above 3000 feet. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 20 percent.

Friday: Sunny. Isolated showers in the afternoon. Highs 79 to 86 near the shore to around 74 above 3000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Friday Night: Partly cloudy with isolated showers. Lows 65 to 70 near the shore to around 59 above 3000 feet. Light winds. Chance of rain 20 percent.

South Kaua’i

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 70. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

Friday: Mostly sunny with isolated showers. Highs 78 to 85. East winds 10 to 15 mph. Chance of rain 20 percent.

Friday Night: Mostly cloudy with scattered showers. Lows around 69. Northeast winds around 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 58 to 68 in the valleys to around 56 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 74 to 79 in the valleys to around 64 above 4000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

Friday Night: Partly cloudy with scattered showers in the evening, then mostly cloudy with numerous showers after midnight. Lows 60 to 68 in the valleys to around 57 above 4000 feet. East winds around 10 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Partly cloudy with scattered showers. Lows 62 to 69. East winds up to 15 mph shifting to the southeast after midnight. Chance of rain 40 percent.

Friday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 75 to 83. East winds up to 15 mph. Chance of rain 30 percent.

Friday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 62 to 69. East winds up to 10 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 62 to 72. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 71 to 83. East winds around 10 mph. Chance of rain 40 percent.

Friday Night: Partly cloudy with scattered showers in the evening, then mostly cloudy with numerous showers after midnight. Lows 63 to 72. East winds around 10 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A upper level trough west of Kauai will weaken as it moves east over the Hawaiian Islands the next couple of days. This will create enough instability to allow periods of enhanced windward showers. Breezy trades will focus greater rain amounts over windward mauka slopes and higher terrain. An approaching front will weaken local winds and could increase shower coverage over the western end of the state during the first half of next week.

Discussion

At the surface, a weak trough is located approximately 550 miles west of Kauai this morning, while high pressure builds far northeast of the state, driving breezy trade winds across the area, especially along ridgelines and through valleys/mountain passes. Satellite and radar imagery shows the large swath of cirrus from this morning has moved off to the east, revealing isolated to scattered low clouds and isolated showers moving into windward areas on the trade wind flow. This pattern will persist into the first part of the weekend as both surface and upper-level troughing washes out and high pressure and associated ridging become the dominant features over the Central Pacific. Model guidance continues to show an area of low and mid-layer moisture moving in from the east on Friday, so expect a slightly wetter day than today, with the highest rainfall accumulations sticking to the windward slopes of the islands.
Models continue to show a pattern change this weekend a trough and associated front approach the area from the west. Winds will drop off significantly through the weekend, becoming light and variable by Sunday, with land and sea breeze characteristics. A drier low- level airmass should keep afternoon sea breeze showers minimal during this time. The latest global models have backed off on the eastward progress of the front, stalling and washing out the front near Kauai early next week. This would result in light to moderate east-southeast to southeast flow over much of the island chain with stronger northeast winds remaining just off to the northwest Monday through midweek. We could still see some enhanced showers focus along east and southeast facing slopes, especially over the western half of the state, though mostly zonal flow aloft would keep rainfall amounts somewhat in check. Have nudged the PoP grids for this period toward the NBM, which reflects the overall downward trend in forecast precip of the global models. As of now, confidence is increasing that widespread flooding will not be an issue, but will continue to monitor for any model changes that suggest otherwise. Winds could lighten back up over the western end of the state later on Wednesday as a developing trough to the northwest passes by to the north. Confidence becomes much lower in the forecast for the second half of next week as models disagree on their handling of the evolution of that trough and another far northwest of the state.

Aviation

Moderate to locally breezy trades. Low cigs and SHRA will primarily affect windward and mauka locations. MVFR conds can be expected in SHRA otherwise VFR will prevail.
AIRMET Tango remains in effect for mod with isol severe turb from FL250-400, with SIGMET SIERRA series issued for severe turb from FL270-400, due to a subtropical jet over the islands.

Marine

A ridge of high pressure will remain north of the state through tomorrow maintaining moderate to locally strong trades across the islands. A Small Craft Advisory (SCA) for the typically windy waters surrounding Maui County and Big Island is in effect through tomorrow afternoon. The ridge will then weaken and get pushed east on Saturday as a cold front approaches from the northwest. Winds will gradually weaken and veer slightly out of the east southeast starting late Friday evening and becoming light and variable statewide Sunday. The front now looks to stall out just north of Kauai, keeping east southeast winds in place through the beginning of next week.
A small, medium period northwest (310-330 degrees) swell will continue to slowly lower through tomorrow morning. A new moderate, long period northwest swell (330 degree) will then fill in and peak just below advisory levels tomorrow night into Saturday. A large, possibly extra large, long period northwest swell (330 degree) originating from a hurricane force low is expected to reach the islands Sunday and peak Sunday night into Monday. This swell could produce warning level surf along exposed north and west- facing shores during the peak. In addition sea levels will likely rise above SCA criteria.
Expect east shore surf to remain elevated and choppy through tomorrow and ease slightly over the weekend as winds decrease. Small south shore surf sets will persist through the forecast period as several very small, long period south swells move through.

HFO Watches/Warnings/Advisories

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

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