West Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 78 to 83 near the shore to around 69 above 3000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then showers after midnight. Lows 62 to 67 near the shore to around 55 above 3000 feet. North winds up to 20 mph. Chance of rain 90 percent.

Saturday: Cloudy and breezy. Showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 77 near the shore to around 64 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 80 percent.

South Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 83. West winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows around 64. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Saturday: Cloudy and breezy. Numerous showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 71 to 78. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with showers in the afternoon. Highs 73 to 79 in the valleys to around 63 above 4000 feet. Southwest winds up to 15 mph. Chance of rain 80 percent.

Tonight: Breezy and showers. Lows 55 to 64 in the valleys to around 52 above 4000 feet. North winds up to 20 mph increasing to 10 to 20 mph after midnight. Chance of rain near 100 percent.

Saturday: Breezy. Showers in the morning, then showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 64 to 71 in the valleys to around 55 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain near 100 percent.

North Kaua’i

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with showers in the afternoon. Highs 72 to 80. South winds up to 15 mph shifting to the northwest in the afternoon. Chance of rain 80 percent.

Tonight: Breezy and showers. Lows 57 to 65. North winds 10 to 25 mph. Chance of rain near 100 percent.

Saturday: Breezy. Showers in the morning, then showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 66 to 76. Northeast winds 10 to 25 mph. Chance of rain near 100 percent.

East Kaua’i

Today: Mostly sunny in the morning, then partly sunny with numerous showers in the afternoon. Highs 73 to 83. Southwest winds up to 15 mph. Chance of rain 70 percent.

Tonight: Showers. Lows 58 to 67. North winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain near 100 percent.

Saturday: Breezy. Showers in the morning, then showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 64 to 75. Northeast winds 10 to 20 mph. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

A cold front will approach from the northwest today, move into Kauai late this afternoon, then through Oahu and into Maui County tonight. The front will bring an increase in clouds and showers as it moves through, eventually stalling out across the central islands this weekend. Plentiful moisture will pool along the stalled front, and this combined with a disturbance aloft moving overhead, will bring the potential for heavy rainfall, flash flooding and even a few thunderstorms Saturday afternoon through Monday afternoon. Breezy north to northeast winds will develop behind the front tonight and Saturday, with conditions then becoming very windy late Sunday through early next week as a strong high passes by well north of the state. Conditions will gradually improve by the middle to latter part of next week, although somewhat showery and breezy trade wind weather should prevail.

Discussion

Currently at the surface, a 1021 mb high is centered several hundred miles east-northeast of the state, with a ridge axis extending west-southwestward and over the Big Island. Meanwhile, a cold front is located about 85 miles northwest of Kauai as of 3 am HST. Light to moderate south to southwest winds prevail over the smaller islands early this morning, while light to moderate southeasterly flow persists over the Big Island. Infrared satellite imagery shows a band of scattered to broken low clouds over Oahu and Maui County. With mostly clear conditions across Kauai, and all but southeast slopes of the Big Island. Radar imagery shows scattered showers affecting Maui County, a few showers over east and southeast facing slopes of the Big Island, with dry conditions elsewhere. Main short term focus revolves around the big pattern change expected during the next few days.
The cold front northwest of the islands will track steadily southeastward today, eventually slowing and stalling out in the vicinity of Maui County late tonight and Saturday. An increase in clouds and showers is expected to accompany the front, along with breezy north to northeast winds developing in its wake. The front will gradually weaken and dissipate by late Sunday, while a strong high builds north of the state. Abundant moisture will pool along the stalled front while a strong disturbance aloft moves overhead, bringing the potential for heavy rainfall, flash flooding and even a few thunderstorms to the area. The latest GFS/ECMWF solutions, their ensembles, as well as their AI versions support the potential for flash flooding Saturday afternoon through Monday afternoon, and as a result, a Flood Watch has been issued. Cold temperatures aloft associated with the upper disturbance moving through will support the potential for heavy snow on the Big Island summits, and as a result, a Winter Storm Watch has been issued Saturday afternoon through Monday afternoon as well.
Well if that is not enough to be concerned about, very windy conditions are forecast to develop by late this weekend and continue through early next week, as a strong area of high pressure builds north of the islands. A Wind Advisory will likely be required for the entire state beginning late Sunday and continuing through at least Tuesday. Portions of the state could even see winds reach High Wind Warning levels, particularly over and downslope of terrain, through valleys, and other local acceleration areas.
Conditions will gradually improve for the middle and latter portion of next week, although a somewhat showery and breezy trade wind pattern will likely persist.

Aviation

A strong cold front is on approach and sits northwest of Kauai. By late morning the front with accompanying SHRA and breezy northerlies will be on Kauai's doorstep. This front is expected to slowly move down the island chain through Monday. SHRA/TSTMS with IFR/MVFR conds will be possible with areas behind FROPA returning to VFR.
No AIRMETs in effect. AIRMET Sierra may be needed at various times as the front moves through the island chain through this weekend.

Marine

A front just northwest of Kauai will move down the island chain late today and tonight. Gentle to moderate southerly winds ahead of the front will be replaced by moderate to locally strong northerly winds as the front moves over Kauai and Oahu waters this afternoon and evening before stalling over the eastern half of the state overnight tonight into Saturday. The front will gradually dissipate near Maui County over the weekend leading to heavy showers and thunderstorms statewide. A Small Craft Advisory (SCA) has been issued for waters around Kauai and Oahu and will likely need to be expanded to windward Maui waters this afternoon, as a large northwest swell produces seas above the 10 foot SCA threshold. Surface high pressure will expand significantly later Saturday afternoon through Sunday as surface troughing develops southwest of the islands. As a result, trade winds will strengthen to near gale to gale force over many areas, with SCA conditions developing over all waters for winds and seas late Sunday and hold through Monday. A slow decrease in trade winds is expected Tuesday and Wednesday, but large seas will persist.
Surf along exposed north and west shores will be just below High Surf Advisory (HSA) thresholds this morning as a pulse from the current moderate, medium period northwest swell quickly moves through. A new large, long period northwest swell (300-315 degrees) is expected to overlap the current swell and fill in locally through the morning hours. A HSA for north and west shores of Kauai and Oahu has been issued starting at noon today as surf is expected to rise above HSA thresholds with this rising swell. Surf is then expected to exceed High Surf Warning levels overnight tonight as this swell peaks, and the HSA will likely be upgraded and expanded to include north and west facing shores of Molokai and north facing shores of Maui. The swell will decline sharply Saturday afternoon into the evening, with surf expected to fall below advisory levels by Sunday morning. Small to moderate north- northwest swells will prevail through the remainder of the week.
Surf along east facing shores will remain very small through tonight. Surf is expected to rapidly build and become rough this weekend, likely exceeding the advisory level Sunday night or Monday and potentially reaching warning level Tuesday or Wednesday. Surf along south facing shores will remain small with a slight bump early next week.

HFO Watches/Warnings/Advisories

High Surf Advisory from noon today to 6 PM HST Saturday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Kauai North.
Flood Watch from Saturday afternoon through Monday afternoon 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, Haleakala Summit, 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.
Winter Storm Watch from Saturday afternoon through Monday afternoon for Big Island Summits.
Small Craft Advisory from noon today to 6 PM HST Saturday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters.

Data Courtesy of NOAA.gov