Photo Credit: Braden Jarvis

West Kaua’i

Rest Of Today: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 83 near the shore to around 72 above 3000 feet. Southeast winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Breezy. Mostly cloudy with showers likely and slight chance of thunderstorms. Lows around 73 near the shore to around 67 above 3000 feet. Southeast winds 10 to 20 mph. Chance of rain 70 percent.

Friday: Mostly cloudy with numerous showers and slight chance of thunderstorms. Highs around 84 near the shore to around 72 above 3000 feet. Southeast winds up to 15 mph shifting to the south in the afternoon. Chance of rain 70 percent.

South Kaua’i

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Kaua’i Mountains

Rest Of Today: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 71 to 78 in the valleys to around 62 above 4000 feet. South winds up to 20 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy with showers likely and slight chance of thunderstorms. Lows 66 to 71 in the valleys to around 62 above 4000 feet. South winds up to 15 mph. Chance of rain 70 percent.

Friday: Mostly cloudy with numerous showers and slight chance of thunderstorms. Highs 71 to 78 in the valleys to around 62 above 4000 feet. South winds up to 15 mph. Chance of rain 70 percent.

North Kaua’i

Rest Of Today: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 74 to 83. South winds up to 20 mph. Chance of rain 80 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 68 to 74. South winds up to 15 mph. Chance of rain 50 percent.

Friday: Mostly cloudy with numerous showers and slight chance of thunderstorms. Highs 74 to 83. South winds up to 15 mph shifting to the southwest in the afternoon. Chance of rain 70 percent.

East Kaua’i

Rest Of Today: Breezy. Cloudy with showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 74 to 82. South winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy with showers likely and slight chance of thunderstorms. Lows 64 to 75. South winds 10 to 15 mph. Chance of rain 70 percent.

Friday: Mostly cloudy with numerous showers and slight chance of thunderstorms. Highs 74 to 82. South winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Moist and humid conditions with south to southeast winds will persist into the weekend due to a kona low located west of the islands. Showery conditions with periods of heavy rainfall are expected, which will keep the threat for flooding up. In addition to the rainfall potential, thunderstorms are possible, with a few potentially becoming strong today. Conditions should begin to improve later this weekend through early next week as drier air moves in and the trades return.

Discussion

Deep tropical moisture pooling northward over the state due to a kona low to our west supports moist and humid conditions with southerly flow persisting into the weekend. Satellite-derived precipitable water data reflect this and depict a large band of 2+ inch values extending northward into the area from the deep tropics. Showery conditions with periods of heavy rainfall will continue, which could lead to flash flooding where the rainfall becomes focused or anchors for a given amount of time. Given the lack of focus at the surface, expect the rainfall to develop in bands and move through periodically. Uncertainty in predicting exactly when and where these bands will develop and move through remains high. Overnight, the bulk of the activity has been focused over the Big Island and around Hana on Maui, where measured rainfall totals on the Big Island were around 2 inches in 6-Hrs through 2 AM HST. The activity on Maui has been highly localized around Hana due to anchoring, with estimated rainfall rates coming in around 3-5 inches in 3-Hrs.
In addition to the rainfall potential, enhanced kinematics associated with a band of 40+ knots of deep layer shear (0-6 km) evolving over the western end of the state plus the added instability with lowering upper heights and forcing support a few strong storms developing today. For the Big Island Summits, areas of showers developing and lifting northward in the area will keep the potential in place for a wintry mix, which has led to the extension of the Winter Weather Advisory.
Conditions should begin to improve late in the weekend through early next week with drier air moving in and as the trades return.

Aviation

A kona low west of the state will keep moderate south to southeast winds and produce moderate to locally heavy showers across the Hawaii Region through Friday. Bands of heavy showers are expected with periods of MVFR and brief IFR conditions across the state.
AIRMET Sierra remains in effect for mountain obscuration over Kauai, Oahu, Molokai, Lanai, Maui and the Big Island. These conditions may continue into Friday due to moderate to heavy shower activity.
AIRMET Tango remains in effect statewide for moderate midlevel turbulence in the 120 to FL180 layer due to wind shear and convection caused by the kona low. This AIRMET will likely continue into Friday.
Light icing in layered clouds will remain a concern across the islands as well. Icing potential could possibly increase to AIRMET Zulu level later today as deep layered moisture increases across the region.

Marine

A kona low located west of Kauai and surface high pressure to the distant northeast will keep moderate to strong south to southeast winds in place through Friday. A Small Craft Advisory remains in effect for portions of the eastern waters through 6 pm this evening, and this may need to be extended in time. Winds will ease and shift back to trades this weekend as the kona low weakens into a broad trough west of the state and surface ridging redevelops to the north. The trades will gradually strengthen next week as a new high builds to the distant north and northwest.
A new small to moderate, medium period northwest will peak today, then gradually lower through Saturday. A new moderate, long period northwest swell will start to fill in Saturday, peak near advisory levels on Sunday, then slowly subside Monday. A new north-northwest reinforcing swell is forecast to arrive Monday night, and could push surf up above the advisory threshold Tuesday and Wednesday. Expect choppy conditions along south facing shores due to persistent southerly winds mixed with small, long period south swells during the next couple days. Less choppy conditions can be expected over the weekend. Surf along east facing shores is expected to hold near seasonal levels during the next couple days, then lower below average over the weekend into early next week. Strengthening trade winds could boost east shore surf up above seasonal levels around the middle of next week.

HFO Watches/Warnings/Advisories

Flood Watch through Friday afternoon for all Hawaii islands,
Winter Weather Advisory until 6 AM HST Friday for Big Island Summits.
Small Craft Advisory until 6 PM HST this evening for Maui County Windward Waters, Maui County Leeward Waters, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters.

Data Courtesy of NOAA.gov