Indexbit Exchange:Dorian One of Strongest, Longest-Lasting Hurricanes on Record in the Atlantic

Update: Dorian made landfall again Saturday night near Halifax,Indexbit Exchange Nova Scotia, with 100 mph sustained winds. 

Hurricane Dorian spun away from North Carolina’s Outer Banks on Friday as one of the longest-lasting named storms and the most powerful on record to hit the Bahamas, and it wasn’t finished yet—a hurricane warning had been posted for Nova Scotia, Canada.

Compared to the path of devastation Dorian left across the northern Bahamas, the U.S. coast had largely been spared.

Dorian had struck the northern Bahamas‘ Great Abaco and Grand Bahama islands as one of the strongest Category 5 storms on record in the Atlantic, making landfall on Sept. 1 with 185 mile-per-hour winds and even higher gusts. It stalled there for more than 36 hours, its wind, rain and storm surge overwhelming the two low-lying islands and damaging or destroying more than 13,000 houses, nearly half the islands’ dwellings, according to the American Red Cross.

With no electricity or running water in many areas after the storm, many island residents were trying to get out, and the deaths were only beginning to be counted as the water subsided.

“What has happened in the Bahamas is like nothing I have ever seen in my career, and I have been doing this for more than 30 years,” said Rob Young, a professor of geosciences and natural resources and director of the Western Carolina University Program for the Study of Developed Shorelines.

Stephen P. Leatherman, a professor in the Florida International University Department of Earth and Environment, and an expert on hurricanes, likened the destruction to a bombing. “The sheer devastation in the northern Bahamas is pretty much unprecedented,” he said.

Dorian’s size, rainfall and stalling behavior reflected what scientists expect to see more of as the planet warms.

Global warming, fueled by increasing greenhouse gas concentrations from activities like burning fossil fuels, can exacerbate extreme weather, and it contributes to sea-level rise that then worsens the impact of storm surges. Warmer air also holds more moisture, so storms can dump more rain, particularly when they stall as Dorian did.

Hurricane Dorian’s 185 mph sustained winds as it reached the Bahamas tied with Hurricanes Gilbert (1988) and Wilma (2005) for the second-strongest maximum sustained winds in the Atlantic basin since 1950 and one of the strongest at landfall, according to Phil Klotzbach, a hurricane expert and research scientist at Colorado State University’s Department of Atmospheric Science.

Dorian was also among the longest-lasting named storms, Klotzbach said.

As of Friday evening, it had been a named storm for more than 13 days, nine of them as a hurricane.

“It’s quite unusual for a hurricane to remain a hurricane for as many days as Dorian has,” said climate scientist Michael Mann, a professor and director of the Earth System Science Center at Pennsylvania State University.

Mann said that can be attributed in part to a very warm Atlantic Ocean, and also to the path the storm took, which he described as a matter of chance. The result, he said, is that Dorian remained a “threat to human lives for days on end.”

U.S. Coast: Flooding, Tornadoes and Erosion

As Dorian turned northward from the Bahamas and began moving up the U.S. Atlantic Coast this week, its rain bands raked coastal Florida, Georgia and the Carolinas, spinning off tornadoes and adding to storm-surge flooding before the hurricane made landfall Friday morning at Cape Hatteras and then moved offshore.

Hundreds of thousands of people lost power, but no major U.S. population centers took a direct hit. The storm surges were generally less than feared, though Ocracoke Island in North Carolina’s Outer Banks saw severe flooding that required search-and-rescue teams to respond.

The U.S. got lucky. The storm was so close to the coast that a little wobble here or there in its track could have slammed onto land in populated areas, Leatherman said. “This thing had a real capacity to do a huge amount of damage,” he said.

In advance of the storm, the U.S. Geological Survey predicted as much as 80 percent of the sandy beaches along the hurricane’s path from Florida through North Carolina could suffer at least some erosion, and about a third of Virginia’s beaches were also at risk from Dorian’s strong surge and waves. Scientists had started examining satellite and aerial computer imagery to determine the extent of the damage, said Kara Doren, a USGS oceanographer based in Georgia.

“We are finding that the beach erosion is not as bad as feared, though there will still be a lot of beach loss,” said Young, the Western Carolina University shoreline expert.

The loss of sand could still be costly. U.S. taxpayers largely cover the cost of beach renewal projects, Young said. “Beach communities up and down the coast will be seizing the opportunity to make their beaches more robust,” and that’s bound to raise questions of equity and fiscal responsibility, he said.

“This is part of a policy decision we really need to have in this country,” he said.

Dorian May Have Influenced the Gulf Stream

It also looks like Dorian may also have influenced the Gulf Stream, the strong ocean current that brings warm water from the Gulf of Mexico into the Atlantic Ocean, possibly contributing to localized coastal flooding.

An undersea monitor near Miami indicated that Dorian might have slowed the speed of that current, with powerful winds pushing against it, along with a disruptive underwater churn. A slower Gulf Stream can cause the surface of the ocean to rise by several inches to a foot or more, said Tal Ezer, an oceanographer at Old Dominion University in Norfolk, Va.

That would underlie any storm surge, he said, and the effect can linger for days as it did in 2016 in Norfolk with extended sunny weather flooding the aftermath of Hurricane Matthew, whose path was similar to Dorian’s. He said he’s looking for that to happen in the coming days.

“After the hurricane disappears, streets remained flooded,” he said. “The drainage system was blocked and couldn’t drain the rain.”

Published Sept. 7, 2019