West Kaua’i

Tonight: Hurricane conditions expected. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Lows around 76 near the shore to around 67 above 3000 feet. East winds 15 to 75 mph shifting to the south 25 to 75 mph after midnight. Gusts up to 120 mph. Chance of rain near 100 percent.

Tuesday: Tropical storm conditions expected with hurricane conditions possible. Mostly cloudy. Frequent showers in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 86 to 91 near the shore to around 79 above 3000 feet. Southwest winds 20 to 40 mph with gusts to 65 mph decreasing to 10 to 30 mph with gusts to 50 mph in the afternoon. Chance of rain 90 percent.

Tuesday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 76 near the shore to around 67 above 3000 feet. Southwest winds up to 15 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Tropical storm conditions with hurricane conditions possible. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 73 to 79. Southeast winds 30 to 55 mph with gusts to 75 mph. Chance of rain near 100 percent.

Tuesday: Tropical storm conditions possible with hurricane conditions also possible. Mostly cloudy. Frequent showers in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 81 to 90. Southwest winds 20 to 35 mph decreasing to 15 to 25 mph in the afternoon. Chance of rain 90 percent.

Tuesday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 73 to 79. Southwest winds 10 to 15 mph shifting to the west after midnight. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Tropical storm conditions 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. East winds 25 to 70 mph shifting to the south 15 to 70 mph after midnight. Gusts up to 125 mph. Chance of rain near 100 percent.

Tuesday: Tropical storm conditions expected with hurricane conditions possible. Mostly cloudy. Frequent showers in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 78 to 86 in the valleys to around 77 above 4000 feet. Southwest winds 15 to 50 mph with gusts to 85 mph decreasing to up to 40 mph with gusts to 60 mph in the afternoon. Chance of rain 90 percent.

Tuesday Night: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows around 72 in the valleys to around 64 above 4000 feet. Southwest winds up to 25 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

North Kaua’i

Tonight: Hurricane conditions expected. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 69 to 77. East winds 30 to 60 mph becoming southeast 10 to 60 mph after midnight. Gusts up to 110 mph. Chance of rain near 100 percent.

Tuesday: Tropical storm conditions expected with hurricane conditions possible. Cloudy with frequent showers in the morning, then partly sunny with scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 76 to 90. South winds up to 40 mph with gusts to 70 mph shifting to the southwest up to 30 mph with gusts to 50 mph in the afternoon. Chance of rain 90 percent.

Tuesday Night: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 68 to 77. Southwest winds up to 20 mph shifting to the south up to 10 mph after midnight. Chance of rain 30 percent.

East Kaua’i

Tonight: Tropical storm conditions with hurricane conditions possible. Frequent showers and isolated thunderstorms. Locally heavy rainfall possible. Lows 70 to 78. Southeast winds 20 to 50 mph with gusts to 90 mph. Chance of rain near 100 percent.

Tuesday: Tropical storm conditions expected with hurricane conditions possible. Mostly cloudy. Frequent showers in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 79 to 89. South winds 15 to 40 mph with gusts to 60 mph becoming southwest 10 to 25 mph in the afternoon. Chance of rain 90 percent.

Tuesday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 69 to 79. Southwest winds up to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Southeast to south winds will strengthen tonight as Hurricane Lowell approaches. The core of Lowell is forecast to pass near Niihau tonight into early Tuesday. Damaging hurricane conditions are expected with numerous threats in place throughout the state. A Hurricane Warning is in effect for Kauai and Niihau and a Tropical Storm Warning is in effect for Oahu. High surf and heavy rain will impact all islands with strong winds mainly impacting the western end of the state.

Discussion

Hurricane Lowell is about 160 statute miles southwest of Kauai this afternoon moving north northeastward at 18 mph as a high end category 2 (maximum sustained winds of 110 mph). The core of Lowell is expected to pass west of Niihau, raising the possibility of hurricane force winds reaching Kauai and Niihau and Tropical Storm force winds reaching Oahu. As a result, a Hurricane Warning is in place for Niihau and Kauai and a Tropical Storm warning is in place for Oahu. On satellite imagery this afternoon, bands of moderate rain with embedded heavy rain and have been moving over Kauai, and to a lesser extent the other islands. The shower frequency and intensity is expected to increase tonight as Lowell makes its closest approach. Winds will also tend to be strongest within the heavier rain bands.
Additional impacts from Lowell are expected statewide, and a few headlines are in effect as a result. A High Surf Warning for south facing shores 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. For surf and other marine impacts, please see the marine section of the discussion below.
The Flood Watch for the state continues through Tuesday due to heavy rain brought in by Lowell and associated rain and thunderstorm bands. Terrain influence will play a big factor with isolated areas receiving significant amounts through the event. Stay alert for the issuance of any future flood advisories or warnings across the state. See hydrology section for additional information.
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. A tornado watch is in effect for Kauai and Niihau. Any tornadoes 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.
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. Moisture may take a bit longer to exit the area as well, so conditions are expected to dry out more gradually into the weekend.

Aviation

Hurricane Lowell continues its track northward, advecting unstable deep tropical moisture northward into the islands. Shower activity will continue to trend higher into Tuesday. MVFR conditions with low cloud ceilings and showers are expected statewide. Heavier showers will produce periods of IFR conditions. Surface winds will continue to strengthen today over the western half of the state, as Hurricane Lowell continues to move north.
AIRMET Sierra for mountain obscuration continues for Kauai Oahu Molokai Maui and the Big Island. This AIRMET will likely continue into Tuesday.
AIRMET Tango was issued for moderate low level turbulence affecting the island of Kauai over and SW thru NW of island mountains. A strong surface wind AIRMET was issued for Kauai and Niihau for wind speeds greater than 30 knots due to Hurricane Lowell approaching the islands.
Light icing continues in a layer between 160 and FL220 due to strengthening low level wind speeds as Lowell approaches the island.

Marine

Hurricane Lowell continues to move northward towards the islands this afternoon. Winds and seas are on the increase as the system approaches, and both are expected to peak overnight as Lowell makes it closest approach to Kauai County. A Hurricane Warning remains in effect for waters west of Kauai County, while a Tropical Storm Warning remains in effect for Kauai Channel, Kauai Windward Waters, Oahu Windward Waters and Oahu Leeward Waters. The Small Craft Advisory remains in effect for all remaining coastal waters for a combination of winds and seas through Tuesday. Winds are expected to increasingly veer to the southeast to south as Lowell approaches and the strongest winds and highest seas are expected for the western end of the state.
Hurricane conditions are expected in the western offshore waters through Tuesday as the center of Lowell tracks just west of Niihau. Any slight deviation in the track to the west or east in the next 12 to 24 hours will have significant differences in impact for the coastal waters around Kauai County. What remains of former Tropical Cyclone Karina remains to the northeast of the islands and is expected to dissipate soon.
South-southwest swell from Hurricane Lowell will continue to build rapidly, and peak tonight as it shifts out of the southwest. As a result, warning level surf along south facing shores will continue to rise, peaking overnight. Due to the track of Lowell west of the main islands, a sharp gradient in swell is expected from west to east. This will bring damaging surf to portions of Kauai County and likely Oahu, with the potential for significant damage to coastal properties and infrastructure, particularly to those areas along the coasts of Kauai and Oahu exposed to the southerly swell. The hurricane swell energy is expected to rapidly decline on Tuesday as Lowell moves away from the islands.
A moderate, long-period south swell will peak overnight and into Tuesday, but will be overwhelmed by the larger swell mentioned above from Hurricane Lowell. This swell will also fade some on Tuesday but will keep south shore surf somewhat elevated through Thursday. A large, medium-period east swell from former Tropical Storm Karina will combine with increasing east to southeast wind wave generated by Hurricane Lowell to keep advisory level surf along east facing shores through Tuesday. Surf along north facing shores will also experience a small increase on Tuesday as Lowell lifts north of the island chain and then fade 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 through tonight to the unstable airmass moving overhead. Temperature inversion heights are expected to remain elevated or non-existent during the next few days.

Hydrology

Thus far, around 6 to 10 inches of rain have fallen on Kauai, 2 to 5 inches on Oahu and Maui County, and around 2 inches on the Big Island. The potential for flooding remains through Tuesday, and a Flood Watch is in effect for the entire state. Due to the amount of rain that has fallen especially over Kauai today, any heavy showers could trigger quick flash flooding. It is possible the watch may need to be extended into Tuesday night or Wednesday depending on the lingering rain bands across the state in the wake of Lowell as guidance suggests. However, will hold off any update to the watch at this time.
Hurricane Lowell is expected to bring additional rain to the islands through Wednesday morning with 4 to 8 inches, isolated 12 inches across Kauai. Oahu and Maui County, 2 to 5 inches, isolated 10 inches. Big Island, 4 to 8 inches, isolated 12 inches. This rainfall may produce significant flash flooding and mudslides, especially across Kauai County and south and east portions of the Big Island. Its important to note that any pop up thunderstorms that develop could dramatically increase total rainfall amounts anywhere.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov