Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny with isolated showers. Highs 83 to 88 near the shore to around 74 above 3000 feet. Northeast winds up to 15 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 66 to 72 near the shore to around 58 above 3000 feet. Northeast winds up to 15 mph.

Wednesday: Breezy. Mostly sunny with isolated showers. Highs 82 to 89 near the shore to around 73 above 3000 feet. Light winds becoming southeast up to 25 mph in the afternoon. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 81 to 89. Northeast winds 15 to 20 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with scattered showers. Lows around 68. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 81 to 88. Northeast winds 10 to 15 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 40 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 71 to 80 in the valleys to around 64 above 4000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with numerous showers. Lows 59 to 66 in the valleys to around 55 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs 70 to 78 in the valleys to around 63 above 4000 feet. Northeast winds up to 10 mph shifting to the north up to 25 mph in the afternoon. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 74 to 85. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 40 percent.

Tonight: Partly cloudy with scattered showers. Lows 61 to 71. East winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Breezy. Mostly sunny with scattered showers. Highs 73 to 83. East winds up to 15 mph shifting to the northeast up to 25 mph in the afternoon. Chance of rain 40 percent.

East Kaua’i

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 72 to 84. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with scattered showers. Lows 60 to 72. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 71 to 83. North winds 10 to 15 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Strong trades will steadily weaken, becoming moderate by tonight as pockets of heavy showers continue to focus over Windward Big Island and Maui. Strong winds develop areawide on Thursday as a cold front races through the area. Winds quickly weaken during Friday with a land and sea breeze pattern possible by the weekend.

Discussion

This morning through early Wednesday evening.
Ridging north of the islands will weaken as it is ushered east by a progressive pattern over the north Pacific. This will result in surface high pressure translating toward the US West Coast and steady weakening of the local pressure gradient today. Strong trade winds of the last two days are quickly coming to an end this morning, though a few gusts up to 40 mph will still be possible during the next several hours in the windiest locales. Moderate trades will be firmly in place by late tonight and will continue into Wednesday evening.
Trade wind showers will remain rather vigorous over windward sections of Maui County and the Big Island. Even as mid-level ridging provides high stability over the western end of the state, incoming showers are being preconditioned beneath an upper low centered east of the Big Island. Rain rates up to 2″ per hour have been observed on radar at times, though coverage has remained widely scattered and brisk trades have ensured heavy rain remain progressive. Weakening background flow tonight will lead to slower forward motion of showers as deeper moisture potentially reaches as far west as Oahu, but no heavy rainfall issues expected.
Wednesday night through Thursday evening.
The well-advertised cold front, now east of Midway Island, quickly advances through the forecast area reaching Kauai and Oahu Wednesday night, Maui County early Thursday morning, and the Big Island during midday Thurs. Forward motion of the front and the trailing wind field are not particularly impressive at press time this morning, but both will be invigorated by a mid-latitude trough that will rapidly deepen north of the islands.
The initial frontal passage will be accompanied by a transient band of trade wind showers and a marked strengthening of northeasterly winds. Model cross-sections across the frontal zone indicate shallow instability courtesy of aggressive cold and dry advection at the top of the boundary layer immediately behind the cold front. Downward momentum transport and attendant wind gust potential will therefore be maximized during and within the first couple of hours after the front passes. If wind gusts do reach the mid/high end of the advisory range (50-57 mph), they would most likely do so within this time window. The greatest threat would be in typical locations prone to local accelerations and downsloping, but exposed windward and north- facing slopes/beaches will also be prime. Because the front will weaken as it moves south, this pop of strong post-frontal winds would be most likely around Kauai and Oahu.
As the front advances south, moderate to high confidence exists in a large portion of the area settling into wind advisory conditions for the remainder of the day Thursday. Backing northeasterly winds may even allow some typically sheltered locations, such as the Kona area on the Big Island, to experience gusty winds.
Thursday night through the weekend.
The trough responsible for driving the cold front through the area will close off and rapidly occlude northeast of the islands. As the surface low quickly deepens and drifts westward, it will begin to wipe out the local pressure gradient from east to west. At this time, the global model consensus suggests rapidly diminishing winds late Friday with a land/sea breeze pattern possible by Saturday or Sunday.

Aviation

High pressure far northeast of the state will maintain locally strong trade winds across the island chain today. Speeds are expected to trend down tonight into Wednesday ahead of a cold front that is approaching the islands from the north.
The trades will allow clouds and showers to focus primarily across north through east sections of the islands throughout the forecast period. Showers have been common throughout the night and early this morning across windward sections of Maui and the Big Island where AIRMET Sierra remains in effect for tempo mountain obscuration. Latest satellite and radar trends suggest that these showers may impact windward Oahu later this morning as well, though there is some uncertainty since they will encounter a more stable airmass.
AIRMET Tango remains in effect for moderate low level mechanical turbulence over and downwind of island mountains. This AIRMET will likely continue through the day today as locally strong surface winds remain in place.

Marine

A tight pressure gradient across Hawaii will result in fresh to locally strong trade winds across the coastal waters through tonight. A Small Craft Advisory (SCA) is in effect for the typical windy waters through tonight. A slight weakening in the winds is forecast through Wednesday as the driving high moves away. In its place, a vigorous cold front will impact the area beginning Wednesday night and continuing through Thanksgiving, which will produce strong to near gale force winds and rough seas in combination with a large north northwest swell. Looking forward into the weekend, a kona low forms on the front northeast of the islands, dramatically weakening our winds across the waters.
The current northwest swell is declining slowly through Wednesday. A much larger north swell will build overnight Wednesday into Thanksgiving Day. The peak of this swell could reach warning levels and it could coincide with the spring high tide during the early morning hours Thursday and Friday. Adding the potential for gale force winds along the cold front, there could be significant overwash issues and large wave run up along north facing shorelines. Latest wave run up forecast from PACIOOS is indicating wave run- up heights around 8 feet. Above 8 feet, overtopping of lower roadways closer to the shore should be expected. Areas exposed to north swells on other shorelines should see a significant rise in surf as the north swell moves in. Looking into the weekend, the same kona low looking to weaken our winds, will send a strong north northeast swell that could potentially reach HSA levels for north facing shores. There is potential for significant harbor surges for Kahului, and Hilo starting Thursday through the weekend associated with both north swells.
Surf along east facing shores will remain rough and choppy associated with the strong trade winds. South facing shores will see minimal energy for the foreseeable future.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST early this morning for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters.
Small Craft Advisory until 6 AM HST Wednesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov