West Kaua’i

Tonight: Mostly clear. Breezy. Isolated showers after midnight. Lows around 74 near the shore to around 64 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Friday: Sunny and breezy. Isolated showers in the morning. Highs 86 to 92 near the shore to around 78 above 3000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Friday Night: Mostly clear. Lows around 73 near the shore to around 64 above 3000 feet. Northeast winds up to 15 mph.

South Kaua’i

Tonight: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows 70 to 77. Northeast winds 15 to 20 mph. Chance of rain 40 percent.

Friday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 79 to 90. Northeast winds 15 to 20 mph. Chance of rain 40 percent.

Friday Night: Breezy. Partly cloudy with isolated showers. Lows 69 to 76. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 69 in the valleys to around 61 above 4000 feet. Northeast winds 10 to 15 mph becoming up to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 75 to 83 in the valleys to around 68 above 4000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows 66 to 71 in the valleys to around 60 above 4000 feet. Northeast winds 10 to 15 mph becoming up to 20 mph after midnight. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly sunny with isolated showers early in the evening, then mostly cloudy with scattered showers. Lows 65 to 75. Northeast winds 10 to 15 mph shifting to the east. Chance of rain 40 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 72 to 89. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 65 to 75. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 40 percent.

East Kaua’i

Tonight: Mostly sunny early in the evening then becoming mostly cloudy. Isolated showers early in the evening, then scattered showers. Lows 66 to 77. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 79 to 86. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Friday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 65 to 76. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Strong pressure gradient between Hurricane Lowell and the subtropical high will bring windy conditions through Friday, before tapering this weekend. Showers will focus windward and mauka. Hurricane Lowell will approach the western end of the main Hawaiian Islands late Sunday, bringing possible surf, rain, wind and flooding impacts particularly to the western portion of the state. The extent of impacts will be determined by the eventual track of Lowell.

Discussion

Hurricane Lowell is 465 miles SSW of Hilo and 585 miles SSE of Lihue at the 11 am HST National Hurricane Center (NHC) advisory. Strong gradient winds resulting from the pressure difference between the storm and the subtropical high the north is resulting in strong trade winds across the islands through Friday. Scattered clouds and showers moving in with the trades will focus across windward slopes but may occasionally reach leeward sides of the smaller islands. A Wind Advisory goes through tonight for portions of Oahu, Maui County and Big Island with sustained winds 20 to 30 mph and gusts to 50 mph. This advisory may need to be extended into Friday, but by Saturday, a weekend Hurricane Karina will begin to disrupt the trade wind flow and likely weaken the speeds a bit. Typical summertime trade winds and night/early morning windward showers are forecast Saturday and through the day Sunday.
Attention will shift late Sunday into early next week to the forecast track of Hurricane Lowell, currently a category 4 hurricane. The NHC track forecast moves Lowell slowly westward through Friday night with an abrupt northward turn and increase in forward speed on Saturday. While confidence is low whether a direct impact will occur or not, Lowell will likely bring some impacts to the state including storm surge, high surf, wind, and rainfall impacts to portions of Hawaii, particularly as it moves closest to Kauai County Monday night. The extent of these impacts could range from minor to major depending on the eventual path of the storm, and more specifically when the abrupt turn to the north occurs. Regardless, Lowell is forecast to be a category 3 hurricane at its closest proximity. Coastal inundation could also be exacerbated by the peak monthly high tides that are expected to occur Monday. Interests in Hawaii should continue to closely monitor the progress of Lowell through the upcoming Labor Day weekend, listen to the advice of officials, and ensure they have their hurricane plan and supply kit in place.
Please visit the hurricanes.gov page for the official NHC forecast for Lowell.
On Tuesday, winds will weaken shift south to southeastly in the wake of Lowell, but lingering shower bands may occur through the day. Karina will weaken to a remnant low and eventually be absorbed into Lowell north of the state midweek. Winds will eventually shift back to trades during the second half of the week with no significant weather events expected.

Aviation

Mostly VFR this afternoon into this evening with the exception of a few MVFR showers on windward locations. Enhanced trades will keep stronger gusts through this evening with decreasing winds overnight. VCSH returns to the windward exposures and higher terrain overnight with locally MVFR cigs returning.
Hurricane Lowell will continue to pass south of the island chain the next couple of days. On this westerly track, regional trade winds will remain strong per a tight pressure gradient between the hurricane 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 persists far north of the Hawaiian Islands and will slowly drift east through the weekend. Currently, Hurricane Lowell is passing near 450 nm south of the islands as it continues to track west. The interaction between the two will strengthen the trade winds across the coastal waters to fresh to locally near gale force. A Small Craft Advisory (SCA) has been extended for all Hawaiian Waters through Friday afternoon and will likely be extended.
The latest track from Hurricane Lowell from the National Hurricane Center is bringing Tropical Storm conditions to the far southern offshore waters this afternoon. Although as Hurricane Lowell turns north, confidence is growing for hurricane conditions to the southwest and western offshore waters on Sunday. How close it gets to the state, is yet to be determined. As for Hurricane Karina, confidence is increasing that Karina will pass to the north and northeast of the state.
Swells from Hurricane Lowell has filled in and will remain elevated above High Surf Advisory (HSA) conditions through Friday. The HSA has been extended due to a reinforcing south swell from Hurricane Lowell and will peak Friday morning. The swell will gradually veer from southeast towards the southwest early next week. While, the forecast for swells and seas for next week will highly depend on the eventual track and intensity of Lowell, confidence is beginning to increase for the potential of extra- large surf (exceeding warning levels) along south and western exposures early next week. Coinciding also with monthly high tides, this will create the potential for impacts to harbor entrances, channels, as well as coastal properties and infrastructure including roadways.
A large, medium-period east swell from Hurricane Karina will steadily fill in Friday into the weekend and will likely produce high end advisory level surf or warning level surf along east facing shores by this weekend.

Fire weather

Trade winds will remain strong and gusty 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 6000 ft to 7000 ft through tonight.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Friday for Niihau, Kauai Leeward, Waianae Coast, Kahoolawe, Maui Leeward West, Kona, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Molokai West, Molokai Leeward South, Lanai Leeward, Lanai South, Maui Central Valley South, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast.
Wind Advisory until 6 AM HST Friday for Waianae Coast, Central Oahu, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kohala, East Honolulu, Honolulu Metro, Ewa Plain, 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 North.
Small Craft Advisory until 6 PM HST Friday for all Hawaiian waters,

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Data Courtesy of NOAA.gov