Photo Credit: Jason Weingardt

West Kaua’i

Today: Showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 83 near the shore to around 72 above 3000 feet. Southeast winds up to 15 mph. Chance of rain near 100 percent.

Tonight: Cloudy with showers and slight chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows around 73 near the shore to around 67 above 3000 feet. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 90 percent.

Thursday: Mostly cloudy with showers and slight chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 83 near the shore to around 72 above 3000 feet. Southeast winds 10 to 15 mph. Chance of rain 80 percent.

South Kaua’i

Today: Showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 81. South winds up to 10 mph. Chance of rain near 100 percent.

Tonight: Cloudy with showers and slight chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows around 73. Southeast winds up to 10 mph. Chance of rain 90 percent.

Thursday: Cloudy with showers and slight chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs around 81. Southeast winds around 10 mph. Chance of rain 80 percent.

Kaua’i Mountains

Today: Showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 71 to 78 in the valleys to around 62 above 4000 feet. South winds up to 15 mph. Chance of rain near 100 percent.

Tonight: Breezy. Cloudy with showers and slight chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows 66 to 71 in the valleys to around 62 above 4000 feet. South winds up to 20 mph. Chance of rain 90 percent.

Thursday: Breezy. Cloudy with showers and slight chance of thunderstorms. Some thunderstorms may produce gusty winds. 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 80 percent.

North Kaua’i

Today: Showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 74 to 83. South winds up to 15 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy with showers and slight chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows 68 to 74. Southeast winds up to 15 mph. Chance of rain 90 percent.

Thursday: Cloudy with showers and slight chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs 74 to 83. Southeast winds up to 15 mph. Chance of rain 80 percent.

East Kaua’i

Today: Showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 74 to 82. South winds 10 to 15 mph. Chance of rain near 100 percent.

Tonight: Cloudy with showers and slight chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Lows 64 to 75. South winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 90 percent.

Thursday: Cloudy with showers and slight chance of thunderstorms. Some thunderstorms may produce gusty winds. Locally heavy rainfall possible. Highs 74 to 82. South winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 80 percent.

Detailed Forecast

Synopsis

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

Discussion

Deep tropical moisture being drawn northward over the state due to a kona low lurking to our west will support moist and humid conditions with southerly flow persisting into the weekend. Showery conditions with periods of heavy rainfall are possible each day, which could lead to flash flooding where the rainfall becomes focused for a given amount of time. High-resolution model guidance reflects this potential and depicts the best chance for this activity focusing over the western end of the state and the Big Island today. Beyond this time frame, there remains some degree of uncertainty as to exactly when and where heavy rainfall will setup and become focused – with model guidance displaying quite the spread. The latest statistical QPF guidance (90th percentile) shows the higher rainfall accumulations holding over the western and eastern end of the state through Thursday, then over the western end Friday into the weekend as some drier air moves in around the Big Island. For the Big Island Summits, a Winter Weather Advisory has been issued to account for expected snow accumulations into Thursday.
In addition to the rainfall potential, a few thunderstorms are possible, especially later today through Thursday as the upper low deepens and draws closer to Kauai. Improving kinematics associated with a band of 40+ knots of deep layer shear (0-6 km) evolving plus the added instability with lowering upper heights will support a few strong storms tonight through Thursday.
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 southerly winds over the region for the next 24 hours. Expect widespread showers to bookend the state this morning as showers associated with the kona low west of Kauai and another disturbance to the east of the Big Island stream north. Showers across the western end of the state look to then spread eastward through the day on Wednesday. Will see MVFR or lower conditions develop as showers increase. Weak instability across the region will also bring a slight chance of thunderstorms and gusty winds. Unsettled weather continues for the next several days.
AIRMET Sierra for tempo mountain obscuration remains in effect for Kauai and the Big Island this morning and may be needed across the remaining islands later today. AIRMET Tango for tempo moderate turbulence aloft may become necessary today as an upper low west of Kauai moves closer to the region. Tempo light icing in layered, showery clouds will remain a concern across the islands for the near future as well.

Marine

A kona low located northwest of Kauai and surface high pressure far north to northeast of the state will produce moderate to fresh south to southeast winds across Hawaiian Coastal Waters through Wednesday. Winds will gradually weaken by Thursday becoming mainly light and variable Friday into the weekend as the kona low weakens to a broad trough over the state and surface ridge develops to the north.
Isolated thunderstorms have continued over and near Kauai and Oahu. Thunderstorms will expand in coverage across the region from Wednesday through the end of the week.
The current medium period north-northwest swell will continue to subside tonight. A new small to moderate, medium period northwest (310-320 degree) swell will arrive Wednesday, resulting in a rise of surf along exposed north and west facing shores that will linger through Friday. Expect choppy conditions along south facing shores due to persistent southerly winds mixed with small, long period south swells through the week. Surf along east facing shores is expected to remain below average also due to persistent southerly winds.

HFO Watches/Warnings/Advisories

Flood Watch through Thursday afternoon for Niihau, Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward.
Flood Watch from 6 AM HST this morning through Thursday afternoon for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Haleakala Summit, Kona, Kohala, Big Island Interior, Big Island Summits, 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 Weather Advisory until 6 AM HST Thursday for Big Island Summits.

Data Courtesy of NOAA.gov