West Kaua’i

Tonight: Mostly clear. Breezy. Lows around 60 near the shore to around 50 above 3000 feet. Northeast winds up to 20 mph.

Friday: Sunny. Highs around 76 near the shore to around 65 above 3000 feet. Northeast winds up to 15 mph in the morning becoming light.

Friday Night: Mostly clear. Lows around 63 near the shore to around 52 above 3000 feet. Northeast winds up to 15 mph.

South Kaua’i

Tonight: Mostly clear. Breezy. Lows around 61. Northeast winds 10 to 20 mph.

Friday: Mostly sunny. Breezy. Isolated showers in the morning. Highs 71 to 78. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

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

Kaua’i Mountains

Tonight: Breezy. Partly cloudy with isolated showers. Lows 52 to 58 in the valleys to around 48 above 4000 feet. North winds up to 20 mph. Chance of rain 20 percent.

Friday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 64 to 71 in the valleys to around 56 above 4000 feet. East winds up to 15 mph. Chance of rain 30 percent.

Friday Night: Partly cloudy with isolated showers. Lows 54 to 61 in the valleys to around 50 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

North Kaua’i

Tonight: Breezy. Partly cloudy with isolated showers. Lows 54 to 64. Northeast winds up to 20 mph. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers. Highs 67 to 76. East winds up to 15 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy. Isolated showers in the evening. Lows 56 to 65. East winds up to 10 mph increasing to 10 to 15 mph after midnight. Chance of rain 20 percent.

East Kaua’i

Tonight: Partly cloudy. Breezy. Isolated showers after midnight. Lows 54 to 66. North winds 10 to 20 mph. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers. Highs 64 to 76. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 55 to 68. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Showers will continue this evening mainly on the Big Island as winds weaken across the state. Cooler mornings are in store Friday and Saturday as relatively dry air has moved in behind today's cold front. Trades will build in Friday and remain through the weekend. Early next week we will likely see a trend to southeast and then southerly winds. Wednesday into Thursday, another boundary moves close enough to increase rain chances over the state.

Discussion

The latest radar data significant showers confined to the Big Island southwest of Cape Kumukahi toward Ainapo and Pahala. These showers will diminish tonight. Weaker showers extended from Kona north and east toward Laupahoehoe. Sprinkles were falling over parts of Oahu and Maui County. The Wind Advisory for the highest mountain summits on the Big Island has been cancelled as wind speeds have decreased below advisory level and are expected to drop off even more overnight. Satellite showed decreasing clouds moving in from the northwest as relatively dry low-level air moves in.
An upper level trough pushed a cold front through the area today. The front was just moving past the Big Island as of 4 PM HST. This will be followed by high pressure at the surface and relatively dry air, leading to cool mornings the next couple of day. Trades return Friday and stay through the weekend. Morning lows will gradually warm each day as low-level air moistens up.
The surface high pressure will move off to the northeast early next week, allowing surface winds to turn out of the southeast Monday and Tuesday and become southerly Wednesday. This will occur in advance of another boundary (decaying cold front or shear line) approaching from the northwest. It's too far out to say with any confidence how far this boundary will move into the islands, but the potential is there for another wet period for the entire state.

Aviation

Breezy post-frontal northwesterlies have filled in across the forecast area. Where the sun has emerged, over the western islands, winds have been quite gusty. Meanwhile, mid-clouds have suppressed heating and potential gustiness over Maui County. Rather uncommon gusty northerlies have built into PHTO and may return again at times overnight and tomorrow. Similarly, a period of gusty NE winds is anticipated at PHKO as post frontal winds veer through this evening.
Lingering showers over Maui County and the Big Island are scattered and light, the exception being the SE slopes of the Big Island where locally heavy showers have been regenerating through the afternoon. AIRMET Sierra for mountain obscuration will remain in effect for the Big Island through at least this afternoon. VFR remains firmly in place for Kauai through Maui and will remain so through Friday while clearing for the Big Island is delayed until this evening.

Marine

A cold front over the southeast waters this afternoon will continue to progress southeastward overnight and exit the offshore waters on Friday. Moderate to fresh northerly winds will continue to fill in behind the front. Meanwhile, an extra large northwest swell will generate large seas through Friday for exposed waters. A Small Craft Advisory (SCA) remains in effect for all Hawaiian waters through Friday afternoon for combined seas above 10 feet, winds strengthening to 25 kt, or both. A high pressure system moving far north of the islands will bring back easterly trade winds across Hawaiian waters from Friday through Sunday. Winds will then weaken and veer southeasterly early next week in advance of the next front.
An extra large, medium to long period northwest (320-340 degrees) swell will continue to fill in this afternoon, peak this evening, then slowly fade through Friday. Observations from NW Hawaii buoy 51001 show that wave heights significantly increased above 20 feet early this morning and have remained above 20 feet through early this afternoon. The Waimea buoy 51201 started seeing an uptick in long period swell energy by mid morning, with a continued rise expected through the evening. A High Surf Warning remains in effect through Friday for exposed north and west facing shores of Niihau, Kauai, Oahu, Molokai, and north facing shores of Maui. Additionally, a High Surf Advisory is in effect for west facing shores of the Big Island. This swell will gradually transition to become more northerly (350-010 degrees) as it fades through the weekend. Surf along north and west facing shores will then linger near advisory levels Saturday before another reinforcing northwest swell arrives Sunday into Sunday night.
Surf along east facing shores will remain small, though will increase slightly Friday into the weekend as trades become re- established across the area. Additionally, some east facing shores sensitive to northerly swells may experience a slight uptick in surf heights this weekend as the fading northwesterly swell becomes more northerly. No noteworthy swells are expected for the next few days for south facing shores.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 PM HST Friday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
High Surf Advisory until 6 PM HST Friday for Kona, Kohala.
Small Craft Advisory until 6 PM HST Friday for all Hawaiian waters.

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Data Courtesy of NOAA.gov