Photo Credit: Brendan Stephen

West Kaua’i

Today: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 88 near the shore to around 76 above 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows around 72 near the shore to around 61 above 3000 feet. Southeast winds up to 15 mph shifting to the east after midnight. Chance of rain 20 percent.

Thursday: Sunny. Highs 85 to 90 near the shore to around 76 above 3000 feet. East winds up to 10 mph.

South Kaua’i

Today: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 83 to 90. East winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 71. East winds around 10 mph. Chance of rain 50 percent.

Thursday: Mostly sunny with isolated showers. Highs 83 to 90. East winds around 10 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs 75 to 83 in the valleys to around 67 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 64 to 70 in the valleys to around 59 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Thursday: Mostly sunny with isolated showers. Highs 76 to 83 in the valleys to around 67 above 4000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

North Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs 79 to 88. Southeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 65 to 73. Southeast winds up to 10 mph. Chance of rain 50 percent.

Thursday: Sunny with isolated showers. Highs 78 to 88. East winds 10 to 15 mph. Chance of rain 20 percent.

East Kaua’i

Today: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 75 to 86. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 64 to 76. East winds up to 10 mph. Chance of rain 50 percent.

Thursday: Mostly sunny with isolated showers. Highs 75 to 87. East winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

The combination of a weakening subtropical ridge to our north, and a gale low well to our northwest, will keep southeast flow blowing over the islands for the next couple of days. Relatively dry air over the islands will keep showers fairly sparse. A few showers are expected over mainly windward and mauka areas, favoring the night and morning hours. Afternoon clouds and perhaps a shower or two will affect some interior and leeward areas as well. Trades will rebuild over the islands about Friday as a new, strong high pushes far north of us. The trades may turn a a bit more wet and breezy this weekend as additonal moisture and instability reach the islands.

Discussion

A vertically stacked gale low is located 550 mi NW of Kauai, moving S about 15 mph and slowing. Mid-level height falls associated with this feature, interacting with the remnant moisture associated with an diffuse, old frontal boundary over the northern main islands, led to an increase in shower coverage overnight. However, aside from windward Kauai, most of these showers have stayed N of the main islands or in the downwind convergence zones brushing the leeward coastal waters. The low level flow has veered to ESE as a result of this gale low and a weakening subtropical ridge far to our N. This is putting the smaller islands partly in the wind shadow of the higher terrain of Maui and the Big Island. Thus, light winds have led to overnight land breezes in many areas.
The convection-allowing models are continuing to show some possibility for downwind convergence-zone clouds and showers to get pulled up over Kauai and Oahu today, in addition to the possibility of a shower or two developing over interior or leeward sections this afternoon as well. Mid-level height falls continuing over the state today will be working against drier air pushing in south of the remnant frontal boundary, so any showers don't seem like they'd amount to much.
Not a lot of change is expected for the next few days with gentle to locally breezy E to SE flow in some exposed windward areas, and the pocket of relatively dry air over the state. This should lead to a hybrid pattern with a few showers over windward areas mainly nights and mornings, but also can't completely rule out a brief afternoon shower or two over a couple of interior and leeward spots which will remain shadowed from the ESE flow.
The gale low will weaken and start to move away on Thu, so that by Friday the flow around the islands will gradually back around to trades from E to W, locally breezy near the Big Island. Cyclonic flow developing aloft early next week could turn the trades somewhat wet over the weekend, although the models are in some disagreement about how much moisture and instability will be available.
The models seem to be in better agreement, though, about a cold front, accompanied by weak mid-level shortwave energy, reinforcing the wet trades Monday night, but this is still far out in time. Also, a high pressure area emerging off the Asian continent on Wed will slide across the N Pacific and strengthen as it does so. The high remains quite strong, near 1040 mb, as it begins to push southward far N of Hawaii early next week. This is very far out in time, but if the deterministic models are correct, could see advisory level trade wind speeds in some areas early next week.

Aviation

Expect moderate to locally breezy winds in today with winds blowing from an east to southeast direction, as a low pressure system sets up northwest of the Hawaii Region and the high pressure ridge shifts northward. Passing showers remain in the short range forecast, with clouds and showers favoring eastern and southeastern slopes of all islands.
AIRMET Sierra remains in effect for mountain obscurations along north through east sections of Kauai, Oahu, Molokai and Maui. This AIRMET will diminish a few hours after sunrise.
AIRMET Tango remains in effect for tempo moderate turbulence over and immediately south through west of all island mountains below 100. This AIRMET will diminish later this morning as wind speeds weaken.

Marine

Fresh to strong southeast winds will persist through Thursday over most windward waters and near the coasts where terrain-induced accelerations are typical with southeast winds. For the Kauai and Oahu waters, expect light to moderate southeast winds through this time, especially over the leeward waters as low pressure lingers northwest of the state. Winds will shift out of a more typical easterly trade wind direction and become strong over most waters this weekend through early next week as strong high pressure builds north of the state and the low weakens and shifts away from the region.
Surf along east facing shores will remain rough through the weekend due to the locally strong east-southeast winds and the fresh trades upstream across the eastern Pacific. Heights may approach advisory levels early next week if the strong winds materialize.
Surf along north and west facing shores will ease today, then pick up Thursday through the weekend as overlapping small, medium period, north-northwest swells arrive and move through.
Surf along south facing shores will remain small through the weekend with mainly a mix of short-period southeast energy and small background south swells moving through.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Thursday for Maui County Windward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov