West Kaua’i

Tonight: Windy. Occasional showers and scattered thunderstorms until early morning, then scattered showers and isolated thunderstorms late in the night. Locally heavy rainfall possible until early morning. Lows around 70 near the shore to around 62 above 3000 feet. Southwest winds 20 to 30 mph with gusts to 50 mph. Chance of rain near 100 percent.

Saturday: Windy. Cloudy with scattered showers and isolated thunderstorms. Highs around 81 near the shore to around 69 above 3000 feet. Southwest winds 20 to 30 mph with gusts to 55 mph. Chance of rain 50 percent.

Saturday Night: Windy. Mostly cloudy with scattered showers. Locally heavy rainfall possible. Lows around 70 near the shore to around 61 above 3000 feet. Southwest winds 15 to 30 mph with gusts to 50 mph. Chance of rain 40 percent.

South Kaua’i

Tonight: Breezy. Occasional showers and scattered thunderstorms until early morning, then scattered showers and isolated thunderstorms late in the night. Locally heavy rainfall possible until early morning. Lows around 70. Southwest winds 20 to 25 mph. Chance of rain near 100 percent.

Saturday: Breezy. Cloudy with scattered showers and isolated thunderstorms. Highs 76 to 82. Southwest winds 20 to 25 mph. Chance of rain 50 percent.

Saturday Night: Breezy. Mostly cloudy with scattered showers. Locally heavy rainfall possible. Lows around 71. Southwest winds 15 to 25 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Windy. Occasional showers and scattered thunderstorms until early morning, then numerous showers and isolated thunderstorms late in the night. Locally heavy rainfall possible until early morning. Lows 64 to 69 in the valleys to around 60 above 4000 feet. Southwest winds 15 to 35 mph with gusts to 55 mph. Chance of rain near 100 percent.

Saturday: Cloudy. Very windy. Numerous showers and isolated thunderstorms early in the morning, then scattered showers and isolated thunderstorms in the late morning and afternoon. Highs 71 to 78 in the valleys to around 62 above 4000 feet. Southwest winds 15 to 40 mph. Chance of rain 60 percent.

Saturday Night: Very windy. Mostly cloudy with scattered showers. Locally heavy rainfall possible. Lows 63 to 69 in the valleys to around 59 above 4000 feet. Southwest winds 15 to 40 mph with gusts to 60 mph. Chance of rain 40 percent.

North Kaua’i

Tonight: Breezy. Occasional showers and scattered thunderstorms until early morning, then scattered showers and isolated thunderstorms late in the night. Locally heavy rainfall possible until early morning. Lows 64 to 72. Southwest winds 15 to 25 mph with gusts to 50 mph. Chance of rain near 100 percent.

Saturday: Windy. Cloudy with scattered showers and isolated thunderstorms. Highs 72 to 81. Southwest winds 15 to 30 mph with gusts to 50 mph. Chance of rain 50 percent.

Saturday Night: Breezy. Mostly cloudy with scattered showers. Locally heavy rainfall possible. Lows 63 to 72. Southwest winds 10 to 25 mph with gusts to 45 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Breezy. Occasional showers and scattered thunderstorms until early morning, then scattered showers and isolated thunderstorms late in the night. Locally heavy rainfall possible until early morning. Lows 65 to 74. Southwest winds 15 to 25 mph. Chance of rain near 100 percent.

Saturday: Breezy. Cloudy with scattered showers and isolated thunderstorms. Highs 69 to 81. Southwest winds 15 to 25 mph. Chance of rain 50 percent.

Saturday Night: Breezy. Mostly cloudy with scattered showers. Locally heavy rainfall possible. Lows 65 to 74. Southwest winds 10 to 25 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

A powerful kona storm will remain anchored northwest of the state producing periods of hazardous weather impacts across the Hawaiian Islands through the weekend. Expect a combination of threats ranging from significant flash flooding, damaging winds, strong to severe thunderstorms, and snow and ice over the highest Big Island summits. Strong southerly to southwesterly will hold through Saturday and producing damaging wind gusts. The highest threats for damaging winds remain along north and east of the island mountains. Unsettled wet weather conditions with decreasing southwesterly wind trends will continue into early next week. This kona storm begins to lift northward on Monday, and unsettled weather will start to ease across the Hawaii region. High pressure will build back in north of the state during the second half of next week allowing trade winds to gradually return from north to south.

Discussion

A powerful kona storm continues to strengthen roughly 800 sm northwest of the state. A broad band of showers with embedded thunderstorms is currently draped across the central island chain with Kauai along the western edge of this cloud band. Moderate to locally heavy showers have been persistent across the state with 12 hour rainfall total reaching 5 to 8 inches for some of the wetter locations from Kauai to Maui County. Southerly winds have strengthen to warning levels today with peak gusts up in excess of 60 mph for these islands. Strong winds in excess of 70 mph have been observed at the summits Haleakala and the Big Island thus a High Wind Warning remains in effect across the state. A Winter Storm Warning also remains in effect for Big Island Summits.
Forecast remains on track showing the kona low deepening to our northwest allowing for the threat of thunderstorms and severe winds and the potential for severe thunderstorms to continue through tonight as this event peaks into Saturday. The main band of moderate to heavy showers will shift eastward tonight and Saturday before becoming nearly stationary over Maui County and the Big Island. Thus a Flood Watch remains in effect for these areas through Sunday night. Bands of showers and thunderstorms are still forecast to impact Kauai and Oahu into Saturday but the overall trend will be coming down for Kauai early Saturday morning and for Oahu Saturday afternoon. The Flash Flooding threats will continue for Kauai through Saturday afternoon and Oahu through Saturday night due to both saturated soil conditions that more easily lead to ground runoff and flooding from even more moderate continuous rainfall rates. The highest flood threats across the state will favor southern and western slopes. These are typically the drier sides of the islands, less accustomed to heavy rain and flooding. Driving under these heavy shower bands will become challenging with ponding of water on area roadways. Current weather trends in this pattern will change rapidly, these threats to life and property will develop swiftly and can affect any location in the Hawaiian Islands. Postpone outdoor activities or travel if possible until early next week as the kona storm begins to drift northward away from the islands and the threat level across the state diminishes.
From Saturday night to Sunday an upper level short wave trough will shift over the state leading to another upward pulse in moderate to heavy shower activity, particularly over Maui County and the Big Island where the main rainband will remain nearly stationary. The threat of thunderstorms will also continue.
Monday and Tuesday, the large kona storm begins to weaken and lift northward, slowly drifting away from the Hawaiian Islands. This means wet weather will continue over and near Maui County and the Big Island but should see improvement elsewhere.
The extended forecast shows various outcomes during the second half of next week. GFS shows a high pressure system building back into position just north of the island chain as earlier as Wednesday while other deterministic and ensemble models show the high building in Thursday with trades bringing more typical brief passing showers over windward mountain areas. Will continue to monitor latest trends.

Aviation

Widespread showers, some heavy, along with isolated thunderstorms, will continue into Saturday. Expect widespread MVFR to IFR with local LIFR. Winds will remain primarily out of the south and increase through the day. Widespread gusts up to and over 35 kt are forecast. There may be a brief break in the rain this evening and overnight, especially for Kauai and Oahu, before showers are expected to become widespread once again during the day Saturday.
AIRMET Sierra remains in effect all islands due to mountain obscuration. This is expected to remain in effect through tonight.
AIRMET Tango remains in effect for moderate upper-level turbulence between FL240 and FL360. and for low-level turbulence due to strong surface winds. Both of these are expected to remain in effect through tomorrow.
AIRMET Zulu remains in effect, as high clouds from these showers present icing concerns between FL120 and FL260. This is also expected to continue through tomorrow.

Marine

ASCAT passes this morning showed gale-force winds in the waters near Oahu and Maui County this morning, and radar signatures supported gale-force winds with some of the strongest bands of showers moving through the area in association with the strong kona storm impacting the area. Gusty winds, steep and fast building seas, and low visibility in heavy showers will continue across the entire marine waters through the weekend.
The Gale Warning near Kauai and Oahu was expanded to include Maui County following the morning ASCAT pass. The Gale Warning was expanded to include waters near the Big Island starting tonight. The winds are expected to weaken near Kauai and Oahu tomorrow, but continue near Maui County and the Big Island through tomorrow night. The winds by early next week will shift westerly and diminish as the storm gains increasing distance far to the north of the islands.
A small, short to medium period west to west-northwest swell will bring small to moderate surf to north and west facing shores through the weekend. Kauai will block some of this swell energy from reaching Oahu and Maui, but it will make it into the west facing shores of the Big Island. Additionally, a small, medium period north swell will peak Saturday before gradually declining.
Rough and choppy surf will continue along south-facing shores due to the south to southeast wind direction, and with the increased winds, is expected to peak just below advisory levels. Once southerly winds diminish early next week, a small to moderate, long-period south swell generated by a gale force low east- southeast of New Zealand will arrive along south-facing shores and build into midweek. Surf along east-facing shores will remain below seasonal levels as south to southeast winds prevail.

HFO Watches/Warnings/Advisories

High Wind Warning until 6 AM HST Sunday for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kona, Kohala, Big Island Interior, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island East, Big Island North.
Flood Watch through Saturday afternoon for Niihau, Kauai,
Flood Watch through late Saturday night for Oahu,
Flood Watch through late Sunday night for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Haleakala Summit, Kona, Kohala, Big Island Interior, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island East, Big Island North.
High Wind Warning until 6 PM HST Sunday for Haleakala Summit, Big Island Summits.
Winter Storm Warning until 6 PM HST Saturday for Big Island Summits.
Gale Warning until 6 AM HST Saturday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Leeward Waters.
Gale Warning until 6 AM HST Sunday for Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel.
Gale Warning until 6 AM HST Sunday for Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov