West Kaua’i

Tonight: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 75 near the shore to around 65 above 3000 feet. Northeast winds up to 20 mph shifting to the east 10 to 15 mph after midnight. Chance of rain 50 percent.

Wednesday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 87 to 93 near the shore to around 79 above 3000 feet. East winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Wednesday Night: Mostly clear. Breezy. Lows around 75 near the shore to around 65 above 3000 feet. East winds 10 to 20 mph.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 71 to 78. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 80 to 90. East winds 15 to 20 mph. Chance of rain 70 percent.

Wednesday Night: Breezy. Mostly cloudy with scattered showers. Lows 72 to 78. Northeast winds around 20 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with numerous showers. Lows around 70 in the valleys to around 62 above 4000 feet. East winds up to 25 mph increasing to 15 to 20 mph after midnight. Chance of rain 70 percent.

Wednesday: Breezy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 75 to 83 in the valleys to around 69 above 4000 feet. East winds 15 to 20 mph. Chance of rain near 100 percent.

Wednesday Night: Breezy. Mostly cloudy with scattered showers. Lows around 70 in the valleys to around 62 above 4000 feet. East winds 15 to 25 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 67 to 76. East winds 10 to 20 mph. Chance of rain 60 percent.

Wednesday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 73 to 89. East winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday Night: Breezy. Partly cloudy with scattered showers. Lows 67 to 76. East winds 15 to 20 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 68 to 77. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 79 to 87. East winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday Night: Breezy. Mostly cloudy with scattered showers. Lows 68 to 78. East winds 15 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Breezy trade winds will become strong and gusty tomorrow afternoon. Trade showers will generally favor windward and mauka areas, particularly during the overnight through early morning hours each day. Hurricane Lowell is about 520 miles southeast of Hilo as of 2 PM HST, and is forecast to pass south of the state late Wednesday through Friday. Winds are expected to remain strong and gusty through Friday as a strong surface pressure gradient develops. The forecast remains uncertain for Labor Day weekend. Lowell is expected to turn north at some point, most likely to the west of the main Hawaiian Islands. Karina is forecast to move west toward the state through Thursday, but then turn northwest and miss us to the north.

Discussion

Radar and satellite show isolated trade showers this afternoon, most notably across Molokai. Winds have been slowly increasing through the day, currently averaging 10 to 20 mph, with gusts 20 to 35 mph.
Models continue to show a spread of possible solutions for the tracks of Hurricanes Lowell and Karina. Lowell is currently forecast by the NHC to continue traveling just north of due west through Saturday before beginning to turn more northwest. Models indicate that it may turn sharply north at some point, most likely when well west of the main islands. However, some models indicate the possibility of an earlier turn which may bring it near or over one of them. Karina is forecast by the NHC to move WNW through Friday, then begin a more NW track into the weekend. This track will take it north of the state. A very few models (out of hundreds) bring it west far enough to move into the main islands. Although odds are good that neither storm will directly strike populated islands, it would be wise to stay aware of new forecasts in the coming days. And finally, Tropical Storm Marie has formed near 15N 110W (a few hundred miles off the Mexican coast). This storm is approximately 10 days away from potentially moving near Hawaii, and will not be discussed in depth at this time.
Winds will increase Wednesday as Lowell moves closer to the islands due to an increasing surface pressure gradient (high pressure to the north, Lowell to the south). This will bring wind speeds up close to advisory level by late Wednesday, and an advisory may be issued if confidence becomes higher. Showers will increase tonight with the approach of a moist surface trough (unrelated to current tropical systems). As the trough moves away to the west late Wednesday, showers will decrease. Thursday and Friday should bring a rather typical number of showers. These showers will be moving a bit faster than normal, and have a better chance to make it briefly over to leeward areas, as they are carried along by moderate to strong trade winds.
Please visit the hurricanes.gov page for the official NHC forecast for Lowell and Karina.

Aviation

00Z TAFS – Near term updates as morning showers faded was to increase the trades through this evening as they're higher than forecast this afternoon. Otherwise, moderate trade winds will persist through this period. Diurnal trends of MVFR conditions and brief showers through the trades will generally favor windward exposures, mauka and higher terrain. Otherwise, VFR conditions will prevail. Hurricane Lowell is forecast to pass far south of the island chain the next few days. On this track, late week trade winds will strengthen as the pressure gradient tightens between Hurricane Lowell and high pressure to the far north.
AIRMET Tango remains in effect for moderate low level turbulence south through west downstream of high terrain. AIRMET Tango will likely be in effect for the foreseeable future.

Marine

A strong surface high will remain nearly stationary far north of the Hawaiian Islands rest of this week, keeping fresh to locally strong trade winds in place. A Small Craft Advisory (SCA) remains in effect for the typically windy waters. The SCA will likely need to be expanded as trade winds gradually strengthen across the state to strong to possible locally gale force late Wednesday through Thursday as Hurricane Lowell passes far south. The offshore waters will likely see tropical storm conditions over the far south waters as the core of hurricane force winds remains just outside the area Wednesday into Thursday. There is still some uncertainty with the forecast track of Lowell, especially late this weekend into early next week as the cyclone begins to gain latitude, which will have significant impacts on the wind, wave, and surf forecast for the region. Adding to the extended forecast uncertainty will be the approach of Hurricane Karina from the east.
A moderate, long-period south swell will continue to fill in overnight and peak Wednesday. Surf along south facing shores should peak below advisory thresholds. This swell will then gradually decline through the rest of the week. A small, medium- period south southeast swell from Lowell has started to fill in overnight through Wednesday before becoming more southerly Thursday through Friday. These combined swells will keep south shore surf elevated near to just below advisory levels. Beyond that point, the surf forecast is highly dependent on the eventual track and intensity of Lowell, which has the potential to be a significant source of south to southwesterly swell through this weekend and into next week depending on how sharply and quickly the cyclone turns to the north.
Trade wind swell energy will keep rough, choppy surf along all east-facing shores through the coming week. Tonight, a small, medium- period east swell arrives from Hurricane Karina that will build through the week and could push east shore surf to advisory thresholds by this weekend and into next week.

Fire weather

Trade winds will increase in speed tonight into Wednesday, and remain breezy into Friday. Gusts to or over 50 mph will be possible in the typical windy areas. Relative humidity values are forecast to remain too high for critical fire criteria to be reached, and fuels are currently rated as not critical. Therefore, the strong winds will not trigger fire weather watches or warnings. The trade inversion is forecast to be 5500 ft to 6500 ft through Wednesday.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov