Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Partly sunny. Highs 87 to 93 near the shore to around 78 above 3000 feet. East winds up to 15 mph.

Tonight: Mostly cloudy. Isolated showers after midnight. Lows around 73 near the shore to around 63 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Thursday: Partly sunny. Breezy. Isolated showers in the morning. Highs around 90 near the shore to around 78 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

Today: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 85 to 92. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 74. Northeast winds around 15 mph. Chance of rain 50 percent.

Thursday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 85 to 92. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy with scattered showers. Highs 76 to 86 in the valleys to around 68 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 66 to 72 in the valleys to around 60 above 4000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Thursday: Breezy. Mostly cloudy with scattered showers. Highs 75 to 86 in the valleys to around 68 above 4000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

North Kaua’i

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 79 to 90. East winds up to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 67 to 75. East winds up to 15 mph. Chance of rain 50 percent.

Thursday: Mostly cloudy with scattered showers. Highs 78 to 90. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 89. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 78. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Breezy. Mostly cloudy with scattered showers. Highs 76 to 88. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Locally breezy easterly trade winds will continue through today and strengthen slightly Thursday and Friday. Trade winds may ease this weekend into early next week as a ridge far north of the state weakens. Tradewind clouds and showers will favor windward and mauka locations, especially during the overnight through morning hours, with minor fluctuations as pockets of moisture moves through. High clouds will stream overhead at times, especially across the western islands.

Discussion

A strong 1030 mb surface high pressure remains 1600 miles northeast and is generating breezy easterly trades locally. An upper level trough far west of the state is producing west- southwesterly flow aloft, streaming scattered high clouds over the state. Latest satellite and radar imagery depict isolated to scattered showers embedded within the locally breezy easterly trade wind flow and along windward and mauka regions. There also the occasional clouds and showers spilling over to leeward locations of the smaller islands. Clouds and showers should become isolated this afternoon, with the exception of the Kona slopes of the Big Island where clouds and showers will develop due to daytime upslope flow. The remaining forecast will generally follow this typical tradewind pattern regime through early next week with minor changes in tradewind strength and cloud and shower coverage.
The surface high will shift eastward and weaken as a front far north of the state tracks east-southeast Thursday. At the same time, another surface high will build far north of the state, behind the front and shift southward. The gradient over the state will tighten, allowing trades to strengthen briefly late Thursday and Friday into the breezy range. High clouds will continue to move over the islands at times throughout the week, though they may thin or diminish by Friday as the upper level trough propagates far west of the state. The tradewind inversion may erode as early as Thursday into the weekend due to the combination of increasing pockets of moisture riding along with the trades, and an upper level trough northeast of the state sinking over the region Friday and lingering into Sunday. This could allow for deeper clouds and enhanced showers embedded in the tradewind flow at times.
A strong low pressure system will develop far northeast of the state and push the surface high to the west, easing the gradient over the state Sunday into early next week. Trades will weaken to the moderate range. During this time, an upper level ridge will build back over the state which should usher the return of a more normal to dry tradewind cloud and shower pattern.

Aviation

Moderate to locally breezy easterly trade winds will persist through the next 24 hours. The same general pattern will hold with clouds and showers favoring windward and mauka areas mainly during the overnight to early morning hours…with the occasional isolated shower making it to leeward locations. Brief MVFR ceilings and visibilities may occur with any of the heavier showers.
AIRMET Sierra is in effect for mountain obscuration across the windward sections of the Big Island. This AIRMET will likely be able to be dropped a little later this morning as satellite and radar are already showing indications of clearing.

Marine

Fresh to strong easterly trade winds will persist through the week, which supports the Small Craft Advisory in effect for the windier channels and waters surrounding Maui County and the Big Island. This advisory may need to be expanded to other waters late Thursday through Saturday as the pressure gradient tightens over the state. Guidance does depict a weakness forming in the ridge far north-northeast of the area by the end of the weekend, which could result in the trades easing Sunday through Monday.
Surf along south facing shores will remain up through the week as overlapping south to southwest swells move through. Observations from the buoys reflect a mix of an outgoing small south swell, and a fresh, long-period small south-southwest swell arriving (51004 southeast of the Big Island is showing this new long-period source coming in just shy of a foot). This new source will linger through Thursday, then begin to ease into the weekend. A similar southwest pulse is expected over the weekend.
Surf along north and west facing shores could come up slightly over the weekend as a medium-period north-northwest swell arrives. Otherwise, trade wind wrap into some northern exposures will be the only source for surf this week.
Surf along east facing shores will remain choppy through the week due to the local and upstream trade winds.

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.

Data Courtesy of NOAA.gov