Hurricane Hone impacting Hawaii, with Gilma waiting in the wings

Two named tropical cyclones will pass within a few hundred miles of Hawaii within a week's time before the end of August, something that has only happened once in recent decades.

Two named tropical cyclones are slated to impact Hawaii over the next several days, with one passing just to the south of the Big Island late this weekend and another that could close in on the String of Pearls before the end of August. AccuWeather meteorologists expect both to have impact on the islands.

Hurricane Hone passing just south of Hawaii

Hone was named on Thursday as a swirling batch of showers and thunderstorms became better organized. Gusty winds, flooding rain and rough seas are expected to continue across portions of the Hawaiian Islands into Monday as Hone moves to the south.

As of midday Sunday, local time, a peak wind gust of 73 mph (at Kohala Ranch) and rainfall amount of 17.90 inches (Hakalau) was observed so far on Hawaii's Big Island. Over 21,000 customers were without power, as well, according to Poweroutage.us.

"Wind gusts of 40-60 mph are expected mainly across the southernmost islands with higher gusts of 60-80 mph possible across far southern portions of the Big Island with an AccuWeather Local StormMax™ of 100 mph," said AccuWeather Lead Hurricane Expert Alex DaSilva

Winds of this magnitude can bring down trees and cause power outages.

While Hone was looking somewhat ragged on Friday, its became better organized this weekend and gained wind intensity reaching hurricane strength at 5 a.m. eastern time on Sunday morning.

Winds can also increase the fire threat across the islands, especially on the western and southern rain-sheltered slopes of mountains and hillsides. A similar setup occurred last August as Hurricane Dora passed to the south. Gusty winds, drought and dry air triggered a deadly and destructive wildfire that became Hawaii's worst natural disaster.

Heavy rain will also continue to occur across portions of the Hawaiian Islands from into the early part of the week.

"A general 1-2 inches of rain can occur across the islands with higher amounts of 2-4 inches on the Big Island and Maui, and even 8-16 inches on the windward side of the mountains of the Big Island with an AccuWeather Local StormMax™ of 20 inches," DaSilva said.

This magnitude of rain can lead to flash flooding and mudslides, especially but not limited to the windward—generally the northern and eastern—sides of the hills and mountains as the storm approaches.

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As the storm moves southwest of the individual islands, shifting winds will bring locally heavy rain to more of the south-facing slopes from Monday to Wednesday.

Even though a direct strike from Hone is not anticipated in Hawaii, the AccuWeather RealImpact™ Scale for Hurricanes on the islands is less than one.

The RealImpact™ Scale factors in more than the Saffir-Simpson Wind Scale for Hurricanes. The Saffir-Simpson scale only measures the wind intensity of the center of the storm and does not account for the size, speed and other impacts even a near-miss from a storm might bring.

Another tropical threat may approach the islands from the east a few days later.

Hurricane Gilma to approach Hawaii later in the week

Wind, seas and rain may increase only a few days after Hone, depending on how much cool water in front of Gilma causes the hurricane to weaken. Gilma first ramped up to a major Category 3 hurricane during the middle of last week and restrengthened to a major Category 4 hurricane early Sunday morning, before again losing some wind intensity later in the day.

While Gilma will continue to move in a generally westerly direction and inch closer to Hawaii, the hurricane's track has been shifting and may continue to do so through the new week.

The core of Gilma is forecast to pass just to the north and east of the islands with impacts ranging from showers, thunderstorms and gusty winds to ramping up on the Big Island, likely to begin late Tuesday night or Wednesday.

Gilma is expected to weaken considerably before reaching Hawaii, and it is possible that it will be reduced to a tropical depression or wind and rainstorm by the second half of the new week.

The combination of both tropical cyclones will likely bring an extended period of rough seas and surf to the islands, which will pose dangers to boarders, swimmers and small craft.

Back-to-back tropical cyclone impacts are extremely rare

Tropical depressions, tropical storms and hurricanes passing near Hawaii are rare but not unheard of.

August tends to be the busiest month in terms of tropical threats to Hawaii, with 30 tropical cyclones affecting the islands since official record-keeping began in 1949. The month represents more than 40% of the approximately 70 impacts by tropical cyclones on the islands throughout the year.

Iniki was the most potent hurricane to directly strike the state. Iniki hit as a Category 4 hurricane on the Saffir-Simpson scale in 1992. The only other hurricane to directly hit the islands was Dot in 1959 as a Category 1.

Two named storms have not passed within 300 miles of the main islands of Hawaii within a week since 1992. In an extremely rare occurrence in September 1992, Iniki was followed three days later by a direct strike by Orlene as a tropical depression. Two systems passed to the south of the islands in eight days in 1994.

Tropical storms and hurricanes do not have to directly strike Hawaii to cause significant danger and damage, which was demonstrated by Dora last August and Hurricane Lane in 2018.

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