West Kaua’i

Tonight: Breezy. Occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 75 near the shore to around 66 above 3000 feet. East winds up to 20 mph. Chance of rain near 100 percent.

Labor Day: Tropical storm conditions expected with hurricane conditions possible. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs around 87 near the shore to around 78 above 3000 feet. East winds 10 to 30 mph. Gusts up to 50 mph in the afternoon. Chance of rain near 100 percent.

Monday Night: Tropical storm conditions expected with hurricane conditions possible. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 77 near the shore to around 68 above 3000 feet. Southeast winds 25 to 50 mph shifting to the south 15 to 50 mph after midnight. Chance of rain near 100 percent.

South Kaua’i

Tonight: Breezy. Occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 72 to 77. East winds 10 to 20 mph. Chance of rain near 100 percent.

Labor Day: Breezy. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 80 to 87. East winds 15 to 20 mph. Chance of rain near 100 percent.

Monday Night: Tropical storm conditions expected with hurricane conditions possible. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 74 to 79. Southeast winds 15 to 45 mph. Chance of rain near 100 percent.

Kaua’i Mountains

Tonight: Breezy. Occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 71 in the valleys to around 63 above 4000 feet. East winds 10 to 25 mph. Chance of rain near 100 percent.

Labor Day: Tropical storm conditions possible. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 70 to 83. East winds 15 to 35 mph. Chance of rain near 100 percent.

Monday Night: Tropical storm conditions expected with hurricane conditions possible. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 73 in the valleys to around 64 above 4000 feet. Southeast winds 25 to 45 mph with gusts to 65 mph. Chance of rain near 100 percent.

North Kaua’i

Tonight: Breezy. Occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 67 to 76. East winds up to 20 mph. Chance of rain near 100 percent.

Labor Day: Tropical storm conditions possible. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 71 to 88. East winds 10 to 25 mph. Gusts up to 50 mph in the afternoon. Chance of rain near 100 percent.

Monday Night: Tropical storm conditions expected with hurricane conditions possible. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 69 to 77. Southeast winds 20 to 45 mph with gusts to 65 mph. Chance of rain near 100 percent.

East Kaua’i

Tonight: Breezy. Occasional showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 69 to 77. East winds 10 to 20 mph. Chance of rain near 100 percent.

Labor Day: Breezy. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 76 to 85. East winds 15 to 25 mph. Chance of rain near 100 percent.

Monday Night: Tropical storm conditions expected with hurricane conditions possible. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 70 to 78. Southeast winds 15 to 40 mph with gusts to 60 mph. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

Breezy easterly trade winds will continue to gradually veer to the east-southeast over the next day or so as Hurricane Lowell approaches the western islands from the south. Lowell is forecast to pass west of Kauai's coastal waters Monday night. A Tropical Storm Warning and Hurricane Watch are in effect for Kauai, Niihau and the surrounding coastal waters as a result. Impacts such as high surf and heavy rain could impact all of the islands.

Discussion

Hurricane Lowell is about 500 miles south-southwest of Kauai this afternoon and is moving northward. Lowell is expected to pass west of the Kauai coastal waters late Monday through Monday night. Tropical storm force winds are expected to reach Kauai and Niihau at the the closet approach, and thus a Tropical Storm Warning is in effect for Kauai County and the surrounding coastal waters. As the track has nudged to the east, it has raised the possibility of hurricane force winds reaching Kauai and Niihau, as a result a Hurricane Watch has also been issued for these areas.
Additional impacts from Lowell are expected statewide, and a few headlines are in effect as a result. The High Surf Advisory has been upgraded to a High Surf Warning for the south swell generated by Lowell for all islands, along with the west facing shores of the Big Island. A High Surf Advisory remains in effect for the east swell generated by former Tropical Storm Karina, which has weakened to a post tropical low which is about 620 miles east northeast of the Big Island this afternoon.
The Flood Watch for the state continues through Tuesday afternoon. Rain being carried in on the easterly trade winds this morning has started to shift out of a slightly southeast direction in response to the winds beginning to veer, and the interaction with the terrain on a few islands has led to some heavier rainfall. Additionally some thunderstorms formed over the Big Island slopes this afternoon bringing heavy rain there. As a result, some flood advisories and warnings have been issued, and more are possible as the event continues to unfold. With Kauai and Niihau being the closest to Lowell, rainfall totals are expected to be highest there, but due to the terrain influence on the Big Island, isolated areas could receive significant rain over the next couple of days. Stay alert for the issuance of any future flood advisories or warnings across the state.
The threat of short-lived, fast-moving tornados/waterspouts will be present mainly near Kauai and Niihau as Lowell makes its closest approach to the islands. These would likely be embedded in rainbands. The threat for tornadoes is lower near the remaining islands, but not zero. The threat for tornadoes should decrease quickly early Tuesday morning.
For surf and other marine impacts, please see the marine section of the discussion below.
Any deviation in track or intensity could also change how these hazards effect the islands.
High pressure is forecast to build back in Thursday through Saturday, bringing in a more typical trade wind pattern with a drier and more stable airmass.

Aviation

Hurricane Lowell continues its track northward, bringing an abundance of tropical moisture along with it. Shower and cloud coverage has already increased today and will continue to increase through the overnight hours. MVFR conditions in low cloud ceilings and showers are expected through Monday. Heavier showers will produce IFR conditions. MVFR/IFR conditions for Kauai County directly associated with Hurricane Lowell will begin on Monday, and tropical storm force winds will likely occur Late Monday – Monday night.
The wind regime will begin veering ESE – SE tonight and through tomorrow. Surface winds will also strengthen overnight and through Monday, especially over the western half of the state, as Hurricane Lowell continues on its northward track.
AIRMET Sierra for mountain obscuration continues for windward areas of Kauai Oahu Molokai Maui and the entire Big Island. This AIRMET will likely be adjusted to cover other areas and islands as shower coverage increases with time.
AIRMET Tango is currently in effect for moderate turbulence between FL270 and FL360 due to an upper level disturbance.
Light icing is possible in a layer between 160 and FL250 due to upper level clouds from the tropical disturbances moving over the state.

Marine

Hurricane Lowell located southwest of the islands continues to move north slowly this afternoon. As it approaches the island chain wind speeds will begin to increase. A Tropical Storm Warning and a Hurricane Watch is in effect for waters around Kauai County through Tuesday afternoon. A Small Craft Advisory has been expanded due to a combination of winds and seas through Monday night. Winds are expected to increasingly veer to the southeast to south as Lowell continues to approach and bring the strong winds to the western end of the state.
Hurricane conditions are expected in the western offshore waters tonight through Tuesday as the center of the storm is expected to track just west of Niihau. Any slight deviation in the track to the west or east in the next 24 hours will have significant differences in impact for the coastal waters around Kauai County. Post Tropical Storm Karina to the northeast of the islands will continue to weaken and dissipate by Monday.
The High Surf Advisory (HSA) has been upgraded to a High Surf Warning (HSW) for all south facing shores through Monday night. Surf will continue to trend in the HSA range through tonight before the south swell from Hurricane Lowell is expected to rise rapidly Monday, and peak Monday night bringing warning level surf to exposed shorelines. This swell may shift out of the southwest late Monday night. Due to the track of Lowell, a sharp gradient in swell is expected from west to east. Coinciding also with the peak monthly afternoon high tides,this could bring the potential for significant damage to coastal properties and infrastructure, including roadways to portions of Kauai and possibly Oahu. Swell energy is expected to drop off quickly on Tuesday.
A large, medium-period east swell from former Tropical Storm Karina will also continue to produce HSA level surf along east facing shores through Monday night. Surf along north facing shores will remain flat except areas exposed to the storm swells. A small medium period northwest swell is expected on Tuesday and will fade through Thursday. By the end of the week, surf along east facing shores could be bolstered by some medium-period swell generated by Hurricane Marie in the East Pacific. Otherwise, expect choppy conditions from easterly trade wind swell through the week.

Fire weather

Fire weather risk will remain low through the forecast period due to increasing moisture moving over the islands in association with Hurricane Lowell. Thunderstorms will be possible through tomorrow due to the unstable airmass moving overhead. Temperature inversion heights are currently near 11,000 ft from Maui to the Big Island, and are expected to remain elevated during the next few days.

Hydrology

The potential for flooding exists through Tuesday afternoon, and as a result, a Flood Watch is in effect for the entire state. Between now and Tuesday afternoon, Hurricane Lowell is expected to bring additional rain to the islands with 6 to 10 inches for Kauai, with maximum totals of 14 inches possible. For the Big Island, 4 to 8 inches of rain is expected with isolated totals of 12 inches, due to the terrain influence with the southeast flow. Across the remaining islands, rainfall of 2 to 4 inches of rain is expected, with Maui having isolated maximum totals of 8 inches possible. This rainfall may produce significant flash flooding and mudslides, especially across Kauai County and portions of the Big Island.

HFO Watches/Warnings/Advisories

Flood Watch through Tuesday afternoon for the entire state of Hawaii.
High Surf Warning until 6 AM HST Tuesday for Big Island South, Big Island Southeast, East Honolulu, Ewa Plain, Honolulu Metro, Kahoolawe, Kauai East, Kauai South, Kauai Southwest, Kipahulu, Kohala, Kona, Lanai Leeward, Lanai South, Maui Central Valley South, Maui Leeward West, Molokai Leeward South, Molokai Southeast, Molokai West, Niihau, South Haleakala, South Maui/Upcountry, Waianae Coast.
Hurricane Watch for Kauai East, Kauai Mountains, Kauai North, Kauai South, Kauai Southwest, Niihau.
Tropical Storm Warning for Kauai East, Kauai Mountains, Kauai North, Kauai South, Kauai Southwest, Niihau.
High Surf Advisory until 6 AM HST Tuesday for Big Island East, Big Island North, Koolau Windward, Molokai Windward, Olomana, Windward Haleakala.
Hurricane Watch for Kauai Leeward Waters, Kauai Northwest Waters, Kauai Windward Waters.
Tropical Storm Warning for Kauai Channel, Kauai Leeward Waters, Kauai Northwest Waters, Kauai Windward Waters.
Small Craft Advisory until 6 AM HST Tuesday for Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters, Big Island Windward Waters, Kaiwi Channel, Maalaea Bay, Maui County Leeward Waters, Maui County Windward Waters, Oahu Leeward Waters, Oahu Windward Waters, Pailolo Channel.

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Data Courtesy of NOAA.gov