Photo Credit: Braden Jarvis

West Kaua’i

Today: Mostly sunny with isolated showers. Highs around 84 near the shore to around 71 above 3000 feet. Northeast winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows around 65 near the shore to around 53 above 3000 feet. Northeast winds up to 20 mph increasing to 10 to 25 mph with gusts to 50 mph after midnight. Chance of rain 20 percent.

Thanksgiving Day: Sunny and windy. Isolated showers in the morning. Highs around 80 near the shore to around 67 above 3000 feet. Northeast winds 15 to 30 mph with gusts to 50 mph. Chance of rain 20 percent.

South Kaua’i

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

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 62 to 68. Northeast winds 15 to 20 mph. Gusts up to 50 mph after midnight. Chance of rain 50 percent.

Thanksgiving Day: Mostly sunny. Breezy. Isolated showers in the morning. Highs around 77. Northeast winds 20 to 25 mph with gusts to 50 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs around 75 in the valleys to around 64 above 4000 feet. Northeast winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Tonight: Windy. Cloudy with frequent showers. Lows around 57 in the valleys to around 49 above 4000 feet. Northeast winds 10 to 15 mph increasing to 10 to 30 mph with gusts to 50 mph after midnight. Chance of rain 90 percent.

Thanksgiving Day: Windy. Partly sunny with numerous showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 71 in the valleys to around 60 above 4000 feet. Northeast winds 20 to 30 mph with gusts to 50 mph. Chance of rain 60 percent.

North Kaua’i

Today: Mostly sunny with scattered showers. Highs 73 to 82. East winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with frequent showers. Lows 57 to 66. Northeast winds 10 to 25 mph. Gusts up to 40 mph increasing to 50 mph after midnight. Chance of rain 90 percent.

Thanksgiving Day: Breezy. Partly sunny with scattered showers in the morning, then sunny with isolated showers in the afternoon. Highs 69 to 78. Northeast winds 20 to 25 mph with gusts to 50 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 74 to 81. North winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 55 to 69. North winds 10 to 15 mph shifting to the northeast 10 to 25 mph with gusts to 50 mph after midnight. Chance of rain 50 percent.

Thanksgiving Day: Mostly sunny. Windy. Isolated showers in the morning. Highs 70 to 77. Northeast winds 20 to 30 mph with gusts to 50 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Expect a brief period of light to moderate trade winds through this afternoon, which will transport low clouds and brief trade showers into the windward sections of some of the islands. A cold front moving down from the northwest will bring a band of showers, very strong and gusty northeast winds, and cooler temperatures for the entire island chain from tonight through Thanksgiving Day. The winds are expected to weaken by late Friday, which may be followed by an afternoon sea breeze and nighttime land breeze weather pattern this weekend.

Discussion

The western end of an east-northeast to west-southwest oriented surface ridge is about 345 miles north of Kahului. In addition, the leading edge of a 150 mile wide band of broken to overcast low clouds and showers associated with a cold front is located about 290 miles north-northwest of Lihue. This leading edge is moving toward the southeast at 10 to 15 mph. This approaching front is causing the surface ridge to gradually erode north of the islands, which continues to relax the pressure gradient across the region. Expect light to moderate trade winds across most of the state today. Satellite imagery and radar reflectivities show scattered to broken low clouds with embedded scattered showers along the windward sides of the islands from Oahu to the Big Island early this morning. These clouds and showers will likely persist through this morning, but may begin to taper off slightly this afternoon.
The forecast models indicate the cold front will move across Kauai and Oahu tonight, Maui County early Thursday morning, and the Big Island during the midday hours on Thursday. In addition, a broad upper-level trough will deepen as it digs down toward the area north of the islands. A band of clouds and widespread showers will likely accompany the passage of the front, which may bring beneficial rainfall to some of the parched leeward areas. A large surface high building in behind the front will also cause the pressure gradient to become very tight. This will result in very strong northeast winds filling in behind the front. In addition, expect noticeably cooler temperatures as we head into the Thanksgiving Holiday Weekend.
As the front advances south, moderate to high confidence exists that very strong and gusty northeast winds will develop starting tonight, and persisting through Thanksgiving Day. Therefore. a Wind Advisory has been issued for Kauai County and Oahu starting this evening. The forecast model cross-sections across the frontal zone indicate shallow instability may develop due to the advection of cool, dry air near the top of the boundary layer immediately behind the cold front. This may produce downward momentum transport, which could produce locally stronger wind gusts during the first few hours immediately after the front passes through. If wind gusts do reach the middle to high end of the Wind Advisory criteria (that is, gusts of 50-57 mph), this would most likely occur during this time window. The areas with the greatest threat for these higher gusts will be the typical locations like mountain ridges and leeward zones that are prone to local accelerations and downsloping from strong northeasterly winds. In addition, exposed north through east facing slopes and beaches may have brief periods of strong wind gusts, especially during and just after the frontal passage. The backing northeasterly winds accompanying the front may even allow some typically sheltered locations, such as the Kona area on the Big Island, to experience locally strong gusty winds Thanksgiving Day. Expect the Wind Advisory to be extended to the central and eastern islands for strong sustained winds and gusts on Thanksgiving Day.
The upper-level trough, which is responsible for driving the cold front through the area, is expected have a closed upper-level low develop northeast of the islands. This scenario would likely result in a surface low with storm-force winds developing far northeast of the state. The forecast models show this low will move slowly westward from Friday into this weekend. This would likely cause the pressure gradient to relax from east to west across the island chain. This would lead to weakening winds starting late Friday. By this weekend, the latest forecast continues to indicate a weather pattern with alternating local afternoon sea breezes and nighttime land breezes is possible.

Aviation

An approaching cold front will weaken the ridge north of the Hawaiian Islands and decrease trade wind speeds through this afternoon. Trade winds will restrengthen behind this cold front as it sweeps across the state later tonight through Thursday. Expect passing showers over windward and mountain areas through the early morning hours with brief MVFR conditions in any shower bands. Increasing clouds, showers and MVFR/IFR conditions are forecast to develop along the frontal band starting over Kauai and Oahu later tonight, and then moving eastward down the rest of the island chain through Thursday afternoon.
AIRMET Tango remains in effect for moderate low level turbulence over and downwind of island mountains. This AIRMET will likely be cancelled later this morning. AIRMET Tango for moderate low level turbulence will likely return for the western islands later tonight as trade winds restrengthen. Another AIRMET Tango may be needed for moderate clear air turbulence from FL280/350 over the eastern islands later today.
AIRMET Sierra for mountain obscuration will likely be needed for some airfields starting tonight as the frontal cloud band passes through each island.

Marine

As the driving high pressure moves far east, it will result in moderate to fresh trade winds across the coastal waters through the day. A vigorous cold front will impact the area beginning late tonight and continuing through Thanksgiving. The front will produce strong to potentially gale force winds and rough seas in combination with a large north swell. Looking forward into the weekend, as the low associated with the cold front develops far east of the islands, it will begin to wipe out the local pressure gradient from east to west dramatically weakening our winds across the waters.
The current northwest swell continues to decline through today. A much larger north swell will build overnight into Thanksgiving Day. The peak of this swell may approach warning levels along north facing shores. It will also coincide with gusty northeast winds and 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 near 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. The same low looking to weaken our winds into the weekend, will also send a strong north northeast swell that should keep large, short to moderate period swell over the islands that could potentially reach High Surf Advisory levels for north facing shores. There is a potential for significant harbor surges for Kahului, and Hilo starting Thursday through the weekend associated with both large swells.
Surf along east facing shores will decline as the trade winds slack into Wednesday with a slight boost Thursday as trade winds ramp up associated with the front. South facing shores will see minimal energy for the foreseeable future.

HFO Watches/Warnings/Advisories

Wind Advisory from 6 PM this evening to 6 AM HST Thursday for Niihau, Kauai, and Oahu.
Gale Watch from this evening through Thursday afternoon for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel.
Small Craft Advisory from 6 PM this evening to 6 PM HST Thursday for Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov