West Kaua’i

Tonight: Breezy. Mostly clear with isolated showers. Lows around 74 near the shore to around 64 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Highs 86 to 92 near the shore to around 79 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tuesday Night: Breezy. Partly cloudy with isolated showers. Lows around 75 near the shore to around 65 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Breezy. Partly cloudy with scattered showers. Lows 71 to 77. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs 80 to 90. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy. Breezy. Scattered showers in the evening, then showers likely after midnight. Lows 72 to 77. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then showers likely after midnight. Lows around 69 in the valleys to around 61 above 4000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Tuesday: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 75 to 83 in the valleys to around 74 above 4000 feet. East winds up to 20 mph. Chance of rain 70 percent.

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

North Kaua’i

Tonight: Partly cloudy with scattered showers. Lows 66 to 75. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 72 to 88. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 67 to 76. East winds 10 to 15 mph. Chance of rain 70 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 67 to 77. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Highs 80 to 87. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy. Numerous showers in the evening, then showers after midnight. Lows 68 to 77. Northeast winds 10 to 15 mph. Chance of rain 80 percent.

Detailed Forecast

Synopsis

Breezy trades will continue in Wednesday with showers generally favoring windward and mauka areas, particularly during the overnight through early morning hours each day. Tropical Storm Lowell is nearly 700 miles ESE of the Big Island. Latest forecast track has Lowell passing south of the Big Island late Wednesday into Thursday. Trade winds are expected to become strong and gusty as early as Wednesday afternoon into Friday as Lowell passes south of the state. Forecast still remains very uncertain for Labor Day weekend, with the potential for Lowell and Karina within the vicinity of the state.

Discussion

Satellite and radar imagery show isolated passing clouds and showers mainly over the windward and mauka areas. Expect chances of showers to increase tonight as a band of showers moves east to west across the state. Outer rainbands and moisture field from Tropical Storm Lowell will begin to fill in during the day Tuesday, increasing chances of passing trade wind showers and dewpoint temperature above 70 degrees. Trade winds will stay breezy due to a strong surface high remaining far north of the area. Overall expect an up tick in passing showers riding in with the breezy trades over the next few days, especially Tuesday night as a small inverted trough, currently along 145W latitude, moves over the state.
Latest forecast from the National Hurricane Center (NHC) has Lowell passing a little over 300 miles south of the Big Island Wednesday night into Thursday as a cat 3 Major Hurricane. While probabilities for tropical storm force winds remain low over the state, the tightening of the pressure gradient over the islands will likely produce very windy and gusty trade wind weather as early as Wednesday afternoon through Friday. Winds could reach advisory thresholds with wind gusts over 50 mph possible during this time. As far as rainfall, the bulk of the moisture will likely pass south of the state. Some of the outer rainbands, especially on the tail end of Lowell and the beginning of Karina could bring in some enhanced trade wind showers around Friday or Saturday.
The forecast spread drastically increases over labor day weekend into early next week as an upper level trough/low develops north of the state. Latest 12Z run of the google DeepMind (GDM) model continues to shows Lowell taking sharp northward turn over the weekend. While confidence has increased on Lowell passing south of the state during the week, the forecast still remains very uncertain over Labor day weekend into early next with several ensemble members of the GDM showing a sharp northward turn. Also during this time, we could see Karina within the vicinity of the islands late this weekend. Please keep an eye out on the hurricanes.gov page for the official NHC forecast for Lowell and Karina.

Aviation

A strong high pressure system far north of the Hawaiian Islands will maintain moderate to breezy trade winds across the region through at least Tuesday. Clouds and showers will generally favor windward and mountain areas through this period as moisture moves in on the trades, bringing brief periods of MVFR conditions. Otherwise, VFR conditions will prevail. Trade wind speeds are expected to increase over the latter half of the week as the pressure gradient between Tropical Cyclone Lowell passing south of the state and the high to the far north strengthens.
AIRMET Sierra is in effect for tempo mountain obscurations for north through east sections of Kauai, Maui and the Big Island due to persistent low cloud and shower coverage. This AIRMET will likely be needed through the afternoon, and possibly through tonight for the eastern end of the state.
AIRMET Tango remains in effect for moderate low level turbulence south through west of island mountains. This turbulence AIRMET will likely continue for the foreseeable future.

Marine

A strong surface high will remain nearly stationary far north of the Hawaiian Islands this week, keeping moderate to locally strong trade winds in place. Tropical Storm Lowell, now in the Central Pacific, is forecast to intensify into a hurricane tonight and will track very close to or move into the southern offshore waters, bringing possible hurricane conditions from Wednesday into Thursday. There is still some uncertainty with the forecast track of Lowell, especially closer to this weekend as the cyclone begins to gain latitude, which will have significant impacts on the wind, wave, and surf forecast for the region. Regardless of Lowell's final path, trade winds will increase by Wednesday afternoon through Friday as a result of the gradient between high pressure to the north, and Lowell to the south. By this weekend, Hurricane Karina, approaching the region from the east, will increasingly be a factor in the forecast of seas and surf as well.
A small long period south swell will hold through tonight before a moderate south swell arrives on Tuesday. This swell will build Tuesday morning and then peak on Wednesday, bringing surf heights to just below advisory thresholds. This swell will then gradually decline through the rest of the week, while at the same time, medium period energy from Lowell could start filling in across south and southeast shores. Swell from Lowell could peak this weekend, and its size will be highly dependent on the track and intensity of the storm. Currently the swell from Lowell, based on its current forecast, is estimated to elevate surf but stay below advisory levels.
Trade wind swell energy will keep elevated surf heights along all east facing shores through the coming week. Later in the week, a medium-period east swell arrives from Hurricane Karina that could push east shore surf to advisory thresholds by this weekend into next week.

Fire weather

Breezy trades continue through Tuesday and then could strengthen as early as Wednesday afternoon through Friday as TC Lowell passes south of the islands. Strong gusty winds over 50 mph will be possible across select areas during this time. While fuel conditions are not at critical levels due to abundant rainfall we have received over the past several weeks, moderate fire danger will be possible for areas mainly due to very windy conditions. Dewpoints are expected to increase in the upper 60s and low 70s by Tuesday afternoon and hold through the week, keeping minimum humidities in the 50s for the most part. A few leeward areas could still see humidities down into the mid 40s especially on Thursday as a pocket of dry air moves in. The exact track of TC Lowell remains uncertain and thus potential for meaningful rainfall remains uncertain at this time. The inversion will hover between 5500 ft and 6500 ft the next couple of days.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov