West Kaua’i

Tonight: Breezy. Occasional showers. Lows around 69 near the shore to around 60 above 3000 feet. East winds 10 to 25 mph. Chance of rain near 100 percent.

Tuesday: Breezy. Mostly cloudy with numerous showers. Highs around 81 near the shore to around 69 above 3000 feet. East winds 15 to 25 mph with gusts to 45 mph. Chance of rain 70 percent.

Tuesday Night: Breezy. Mostly cloudy with scattered showers. Lows around 70 near the shore to around 60 above 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Breezy. Cloudy with occasional showers. Lows around 69. East winds 15 to 25 mph. Chance of rain 90 percent.

Tuesday: Breezy. Cloudy with occasional showers. Highs 74 to 82. East winds 15 to 25 mph. Chance of rain 90 percent.

Tuesday Night: Mostly cloudy with numerous showers. Lows around 70. East winds 10 to 15 mph. Chance of rain 70 percent.

Kaua’i Mountains

Tonight: Windy. Occasional showers. Lows 61 to 67 in the valleys to around 57 above 4000 feet. East winds 15 to 30 mph. Chance of rain near 100 percent.

Tuesday: Windy. Cloudy with occasional showers. Highs 69 to 76 in the valleys to around 61 above 4000 feet. East winds 15 to 30 mph. Chance of rain 90 percent.

Tuesday Night: Breezy. Mostly cloudy with numerous showers. Lows 62 to 68 in the valleys to around 59 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Breezy. Occasional showers. Lows 63 to 71. East winds 10 to 25 mph. Chance of rain near 100 percent.

Tuesday: Breezy. Mostly cloudy with numerous showers. Highs 71 to 81. East winds 10 to 25 mph. Chance of rain 70 percent.

Tuesday Night: Breezy. Mostly cloudy with scattered showers. Lows 63 to 72. East winds 10 to 20 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Breezy. Occasional showers. Lows 63 to 73. East winds 15 to 20 mph. Chance of rain near 100 percent.

Tuesday: Breezy. Cloudy with occasional showers. Highs 68 to 79. East winds 15 to 20 mph. Chance of rain 90 percent.

Tuesday Night: Breezy. Mostly cloudy with numerous showers. Lows 64 to 73. East winds 10 to 20 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A surface trough west of Kauai, along with its parent upper level low, will move southward today. This will continue the threat of flash flooding at least overnight and possibly into Tuesday. Winds will remain moderate to breezy overnight before weakening. Significant snow and ice accumulations were ongoing for the Big Island Summits. The upper level low is expected to weaken over the next two days as the surface trough shifts west of the state, resulting in reduced chances of thunderstorms and heavy rain. Light winds will develop during the second half of the week allowing for sea breezes to develop but showers will only be light to moderate.

Discussion

As of 3 PM HST, showers were plentiful on radar, especially over the Big Island and Kauai County. Skies were mostly cloudy and winds were moderate with widespread coastal gusts of 25 to 35 mph. A flood advisory was in effect for much of windward Big Island, and other islands were being closely monitored but were “well behaved” at this time.
The upper level low (and its associated surface trough) largely responsible for our recent wet weather is located about 400 miles west of Kauai this afternoon, and is forecast to drift slowly SSE overnight and tomorrow. This will keep it close enough to continue to give us an unstable atmosphere capable of supporting heavy rain and thunderstorms (although the remaining thunderstorms are expected to remain off the coast to our west). Therefore the Flood Watch has been extended through Tuesday afternoon. Winds have not developed on the peaks of Big Island to the extent forecast, so we have reduced the High Wind Warning to an Wind Advisory through tonight. The Winter Storm Warning there for snow/ice will remain in effect overnight.
As the upper low continues to weaken, it will drift southwest Tuesday night through Wednesday night, before weakening too much to significantly impact our weather Thursday. Our chances of rain will decrease each day as this occurs, with upper level ridging pushing in from the west to further stabilize the atmosphere. Friday and Saturday, weak ridging aloft will keep us relatively dry and cool, with no significant weather expected. With lighter winds, we will see a shift to sea- and land-breezes that will help alter precipitation patterns away from the typical trade wind (windward and mauka wet/leeward dry) pattern.
Sunday into Monday, long range models show the potential for an upper level trough to push a surface boundary through the state. If this were to occur, it would bring a period of showers and northwest surface winds. More detail will emerge as we get close in time.

Aviation

A trough west of the state will continue to produce unsettled weather tonight into Tuesday. Prevailing MVFR conditions will be common along north through east sections of the islands as breezy to strong east-southeast surface winds bring periods of rain, favoring primarily east and southeast facing slopes and coasts. Some showers could be heavy at times, producing brief IFR conditions, and a Flood Watch remains in effect statewide through 6 am HST Tuesday.
Conditions are expected to gradually improve by Tuesday, though some lingering showers will remain possible, particularly for the western end of the state.
AIRMET Sierra remains in effect for mountain obscuration over windward areas of all islands. These conditions will likely persist through the night. Additionally, AIRMET Tango remains in effect for both mid- and upper-level turbulence, which will likely persist through the night as well. Ellrod guidance shows that some severe turbulence could develop near Kauai by early Tuesday, so interests should continue to monitor for potential SIGMETs relating to upper turbulence closer to the islands. Finally, AIRMET Zulu remains in effect for moderate rime icing across the entire state.

Marine

A trough west of Hawaii will continue showers and possible thunderstorms winding down by midweek. Strong east to southeast winds will impact all waters through Tuesday and produce rough seas. A Small Craft Advisory for both winds and seas remains in effect for the all coastal waters through Tuesday night. Wind and sea conditions will improve mid to late this week as the disturbance moves further west and away from the islands.
A moderate, medium period, north northeast (030-040 degree) swell will veer more easterly and decline tonight. The next small, long period, northwest (310 degree) swell will build late Tuesday and hold through Friday, then rise this weekend with a new north northwest swell (330 degree) likely producing warning surf along exposed north and west facing shores.
A High Surf Advisory remains in effect for exposed east facing shores through Tuesday night due to an easterly swell generated by the local and upstream east winds. Surf will drop through the remainder of the week as winds taper off.
The Coastal Flood Statement will continue through late tonight. Expect minor flooding of low lying coastal areas during the early morning high tides.

HFO Watches/Warnings/Advisories

Flood Watch through late tonight 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.
High Surf Advisory until 6 AM HST Wednesday for Olomana, Kauai East, Kauai South, East Honolulu, Koolau Windward, Molokai Windward, Molokai Southeast, Windward Haleakala, Kipahulu, South Haleakala, Big Island Southeast, Big Island East, Big Island North.
Winter Storm Warning until 6 AM HST Tuesday for Big Island Summits.
Wind Advisory until 6 AM HST Tuesday for Big Island Summits.
Small Craft Advisory until 6 AM HST Wednesday for all Hawaiian waters,

Data Courtesy of NOAA.gov