West Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 65 to 70 near the shore to around 57 above 3000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 80 to 85 near the shore to around 71 above 3000 feet. Southwest winds up to 10 mph. Chance of rain 40 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows around 68 near the shore to around 58 above 3000 feet. Northwest winds around 10 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 67. Light winds. Chance of rain 20 percent.

Wednesday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 78 to 85. West winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows around 67. West winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Isolated showers in the evening. Lows 59 to 66 in the valleys to around 55 above 4000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 73 to 80 in the valleys to around 64 above 4000 feet. Southwest winds up to 10 mph. Chance of rain 40 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 60 to 66 in the valleys to around 55 above 4000 feet. Northwest winds around 10 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy with isolated showers. Lows 61 to 69. Light winds. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers. Highs 75 to 83. South winds up to 10 mph shifting to the west in the afternoon. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 61 to 69. Northwest winds around 10 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy with isolated showers. Lows 60 to 71. Light winds. Chance of rain 20 percent.

Wednesday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 73 to 84. Southwest winds up to 15 mph. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 61 to 72. Northwest winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light winds with land breezes can be expected through tonight. Winds will then become light southwesterly tomorrow as a cold front approaches from the northwest. The front should reach Niihau and Kauai Wednesday night, then stall near Maui Thursday night. Passing moderate showers may accompany this first front. Winds will turn light and northerly after the front passes then potentially turn southerly again Friday into this weekend. Another stronger front looks to approach this weekend, and heavy rain is possible as this front could have more upper level support.

Discussion

A surface ridge just to the N of the islands will gradually weaken tonight and tomorrow as a cold front approximately 360 nautical miles NW of Kauai approaches. Light and variable winds with local land breezes tonight should give way to light southwesterly winds with local sea breezes tomorrow morning. Dry conditions are expected ahead of this front with little rainfall expected for most of the day Wednesday. The front is forecast to approach Kauai Wednesday night, Oahu Thursday morning, and then wash out over Maui county on Thursday evening. Showers will generally be most abundant within the front but could form over any island interiors during the afternoon hours with the sea breezes. Light northerly winds can be expected behind the front, becoming northeasterly by Friday morning with land/sea breezes.
Winds are forecast to start veering to the south by Friday evening, then to the southwest by Saturday ahead of the next anticipated cold front. These southerly winds will push brief showers over south facing portions of the islands, but overall stay light. By late Saturday into early Sunday morning, a stronger and wetter cold front could impact the islands. The front looks to be very moisture rich, with upper and mid level support, stalling near or over the western half of the state. Something worth mentioning is the fact that the upper level trough that is driving this front southward is much stronger than we have seen so far this season. Additionally, forcing factors such as upper level divergence and low level convergence elevates the chances of sustained heavy rainfall. While Sunday is still several days out, the last few model runs have become more aligned on this solution. The forecast has been updated to reflect this change, with increased POPs statewide, especially for Kauai and Oahu. This will require further monitoring for flood potential over the next several days.

Aviation

Light easterly background flow resulted in localized sea breezes and low cloud build ups over the island interiors. AIRMET Sierra is posted for tempo mountain obscurations that will likely continue through the rest of the afternoon. VFR conditions with brief mountain obscurations may occur across the rest of the islands. Land breezes will clear out cloud cover tonight.
By Wednesday morning, moderate southwest winds will build west to east across the state. A few clouds and showers will track in from the southwest on this flow regime Wednesday.

Marine

A ridge of high pressure north of Hawaii will erode from the west as a front approaches the state from the northwest. The front will enter the Kauai waters late Wednesday and move west to east across the state through Thursday and stall and dissipate around Maui County Thursday night. An increase of showers are expected along and ahead of the front with moderate northerly winds following behind it. Another front approaching from the northwest will generate moderate southerly winds this weekend with an increase of showers expected on Sunday.
Current northwest (300-320 degree) swell will be followed by a larger northwest (310-325 degree) swell filling in tonight and peaking during the day Wednesday. Latest buoy readings from buoy 51001 and 51101 are starting to show some new energy in the 16 to 17 second energy bands, but seem to be running below guidance so far. Thus, we have held off on issuing a High Surf Advisory for north and west facing shores for now. We will continue to monitor the latest buoy readings and we are still expecting surf near the High Surf Advisory threshold on Wednesday. As this northwest swell slowly declines Wednesday night, a reinforcing swell from the north- northwest is expected on Thursday. These swells will slowly decline into the weekend. Another moderate, long period northwest swell (320 degree) should gradually fill in on Sunday and could produce surf near the advisory threshold by Sunday evening.
Small, choppy east shore surf will become minimal over the next few days as trades near and upstream become disrupted by approaching fronts. Expect minimal background surf for south facing shores, with a minor south-southwest pulse expected Wednesday afternoon into Thursday.

Fire weather

Conditions should remain below critical fire thresholds through the week with light winds and elevated RH. Temperature inversion heights should linger around 6,000 to 7,000 feet through tomorrow.

HFO Watches/Warnings/Advisories

None.

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