West Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Lows around 65 near the shore to around 55 above 3000 feet. Northeast winds up to 10 mph.

Martin Luther King Jr Day: Mostly sunny with isolated showers. Highs 78 to 83 near the shore to around 70 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy. Lows around 66 near the shore to around 55 above 3000 feet. Light winds.

South Kaua’i

Tonight: Mostly cloudy with isolated showers. Lows around 65. Northeast winds around 10 mph. Chance of rain 20 percent.

Martin Luther King Jr Day: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 82. East winds around 10 mph in the morning becoming light. Chance of rain 40 percent.

Monday Night: Partly cloudy. Lows around 65. Light winds.

Kaua’i Mountains

Tonight: Mostly cloudy with scattered showers. Lows 57 to 64 in the valleys to around 53 above 4000 feet. Light winds becoming southeast up to 10 mph after midnight. Chance of rain 50 percent.

Martin Luther King Jr Day: Mostly sunny with scattered showers in the morning, then partly sunny with isolated showers in the afternoon. Highs 71 to 78 in the valleys to around 62 above 4000 feet. Southeast winds up to 10 mph in the morning becoming light. Chance of rain 50 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Lows 57 to 64 in the valleys to around 53 above 4000 feet. Light winds.

North Kaua’i

Tonight: Mostly cloudy in the evening, then partly cloudy with isolated showers after midnight. Lows 58 to 67. Southeast winds up to 10 mph. Chance of rain 20 percent.

Martin Luther King Jr Day: Mostly sunny. Isolated showers in the morning. Highs 72 to 80. South winds up to 10 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy. Lows 59 to 67. Light winds.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 59 to 71. Light winds becoming northwest up to 10 mph after midnight. Chance of rain 50 percent.

Martin Luther King Jr Day: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs 70 to 81. Southeast winds up to 10 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy. Lows 58 to 69. Light winds.

Detailed Forecast

Synopsis

Trades have become more southeasterly today as ridging aloft moves over the state, and gradually weakening southeast winds will prevail over the next couple of days. Mainly light showers will favor windward and southeast slopes and coasts through Tuesday. A weakening cold front will move into the western part of the state Wednesday, increasing rainfall chances Wednesday through Friday. There remains some uncertainty, but increased showers could linger into next weekend.

Discussion

This afternoon, breezy east-southeast winds are prevailing across the island chain. Latest satellite and radar imagery shows some areas of low clouds embedded within this east-southeasterly flow moving into windward areas. Meanwhile, the typical afternoon cloud buildups have also occurred in sheltered leeward areas, such as the Kona slopes of the Big Island. Showers, on the other hand, have been rather light. Statewide rain gauge networks have reported little to no rain at the vast majority of locations during the daylight hours today, with sites reporting a few hundredths of an inch at most.
A surface high far to our northeast will move even farther northeast over the next couple of days while a front approaches the islands from the northwest. As this occurs, winds will continue to be more southeasterly as they gradually weaken. Predominantly dry and stable conditions are expected to persist through Tuesday, with only a few light showers along windward and southeast slopes and coasts.
The front that is approaching from the northwest is forecast to arrive in the islands on Wednesday, driven by an upper level trough. Model guidance suggests that it will reach Kauai County by Wednesday morning, Oahu in the afternoon to evening, and Maui County overnight Wednesday night into early Thursday. Ahead of the front, light winds will result in a daytime sea breeze/nighttime land breeze regime. However, winds will become breezy to locally strong out of the northeast behind the front. As the front moves through, moisture associated with it will increase shower chances across the islands.
There remain some key differences amongst model guidance regarding what happens from Thursday onward. As was the case with previous model runs, some ensemble members are continuing to show the front moving through Big Island, while others show it stalling and its associated moisture beginning to wash back westward for Thursday and Friday. Regardless, rain chances will increase from Wednesday into Thursday, and higher chances could linger over at least portions of the state through the end of the week. High pressure looks to become re-established north of the islands next weekend.

Aviation

Moderate to locally breezy east southeasterly flow will veer more southeasterly and begin to ease this evening into tonight. By Monday, light to locally moderate southeasterly flow will prevail across the state as a frontal system begins to approach the region from the northwest.
A few light showers may affect eastern portions of the islands through Monday, but with minimal impact to aviation interests. Elsewhere, VFR conditions and mostly clear skies prevail.
AIRMET Tango remains in effect below 7000 ft for low level turbulence downwind of terrain across Maui County and the Big Island due to the gusty east southeast flow. However, the AIRMET will likely be canceled later tonight as winds slowly weaken.

Marine

Winds will weaken and veer southeasterly beginning tonight as the driving high pressure system moves away and a cold front approaches from the northwest. The front will reach the far northwest coastal waters Tuesday night, moving down the the island chain Wednesday and stalling out across Oahu and Maui County into Thursday.
A short-lived northwest swell will peak tonight and decline Monday. This swell will produce advisory level surf across exposed north and west facing shores of Niihau, Kauai and Oahu, and north facing shores of Molokai and Maui, where a High Surf Advisory is in effect through tonight. Buoy readings show a wave high increase at Waimea Bay, and a decrease already seen at the 51001. Another moderate, long period, northwest swell is expected to arrive in the islands Tuesday, and linger through the middle of the week. This swell will maintain elevated surf along north and west facing shores.
As winds weaken and veer to the southeast ahead of the incoming front, surf will lower along east facing shores. There are no noteworthy swells for the next few days for south facing shores.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Monday for north and west facing shores of Niihau, Kauai, and Oahu, and north facing shores of Molokai and Maui.
Small Craft Advisory until 6 AM HST Monday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward 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.

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Data Courtesy of NOAA.gov