EMERALD ISLE — Greg Rudolph, who as Carteret County Shore Protection office manager monitors hurricanes’ impacts on area beaches, said last week predictions of an above average number of tropical storms this hurricane season appear to him to be the “new normal.”
Hurricane season begins each June and runs through November, although for the seventh straight year, a tropical storm, Ana, formed before the officials start.
According to N.C. State University meteorologists, the 2021 Atlantic hurricane season will be above average, with 15 to 18 named storms. Average is considered 11 named storms, calculated using the years 1951 to 2020.
Of this year’s predicted named storms, seven to nine could grow to hurricane strength – above the historical average of six – with two or three becoming major hurricanes, or storms that reach category 3 or higher on the Saffir-Simpson scale.
But Mr. Rudolph said this above average may just be normal now, based on procedures used by the National Oceanic and Atmospheric Administration.
NOAA uses a rolling, three-decade window to determine the climate normal, he said in his annual hurricane prediction analysis in his office’s Shorelines newsletter.
“With the onset of the year 2021, our new average is calculated from 1991-2020 rather than from 1981-2010, and one could argue the last three decades better encapsulate the uptick of tropical cyclone activity that most experts agree started in the 1990s and continues today.”
In addition, Mr. Rudolph told the News-Times, the average total wind velocity for each six-hour period of all tropical storms’ existence – known as the Accumulated Cyclone Energy Index, or ACE Index – for 1991 to 2020 is 121 knots, or 139 mph, up from 104 knots, or 119 mph, in the previous three-decade period.
“The ACE Index is actually one of the more revealing parameters we can use and serves as a better indicator of whether or not a hurricane season is truly “active” or not,” Mr. Rudolph wrote in Shorelines. “That’s a pretty big jump.”
All of this has implications on erosion and beach nourishment, the primary focus of Mr. Rudolph’s office.
The county just finished three years of nourishment, costing more than $85 million, from one end of Bogue Banks to the other. More than 5 million cubic yards of sand were added.
With the “new normal” in numbers and strength of hurricanes per season, however, Mr. Rudolph said there’s no reason to relax or cease monitoring erosion rates, which under the county’s beach management plan trigger new restoration projects.
That new normal “might subconsciously be the reason we’ve started looking for new sand sources,” other than the borrow site in the ocean off Atlantic Beach, he said.
“Our beaches are in good shape now for a moderate hurricane, depending upon the angle of approach and other factors,” he said.
With the ACE index higher from 1991 to 2020,however, it appears likely there will continue to be more strong hurricanes likely to cause the most beach erosion and move the sand farther offshore, where it’s not likely to return to the strand under normal conditions, he said. The likely continuation of the trend toward stronger storms would also threaten more properties, and potentially lives, through erosion and flooding.
Smaller hurricanes generally move sand side to side along Bogue Banks, Mr. Rudolph said, and there is a better chance it stays or returns to the beaches. He particularly mentioned Hurricane Dorian, which in 2019 was at one time a category 5 storm with 185 mph winds in the Bahamas, but made landfall as a category 2 storm at Cape Hatteras that September. According to county beach engineering surveys, it ended up adding sand to Bogue Banks beaches.
As for this year’s predictions on the number of hurricanes and tropical storms, Mr. Rudolph said he analyzed predictions from a number of organizations, chiefly the Tropical Meteorology Project at Colorado State University, the University College of London for Tropical Storm Risk and NOAA.
“There is excellent agreement that we could expect 17 named cyclones, eight of which will generate into hurricanes, with four of these becoming a major hurricane, all above historical values for each category,” Mr. Rudolph wrote in Shorelines, and that’s generally in line with the recently released prediction from NCSU.
But, he added, “It’s important to keep in mind this above-average type of forecast is really predicated upon not what factors are in place now but will be once we hit peak season in September.”
Staff writer Mike Shutak contributed to this report.
Contact Brad Rich at 252-864-1532; email firstname.lastname@example.org; or follow on Twitter @brichccnt.