WILMINGTON — When the system that would become Tropical Storm Colin rapidly strengthened off the coast of South Carolina in the early morning hours of July 2, it caught weather forecasters and beachgoers off guard.
Many were left wondering: Is this an anomaly? Or indicative of climate change — a harbinger of things to come, with storms intensifying more quickly in the future?
According to Steve Pfaff of the National Weather Service, it was not the first time storms escalated swiftly in the Atlantic Basin in July. Still, it’s not necessarily a natural occurrence, he confirmed, at least not in the Wilmington area.
“Fortunately for us, at our latitude, it is rare to have something form as quickly as Colin did,” added Pfaff.
Part of the reason is the Gulf Stream just offshore, typically very warm, is not usually large enough to support the development of a tropical storm in the Atlantic this early in the season — unlike the Gulf of Mexico, Caribbean and tropical Atlantic waters, from the Bahamas to Cape Verde Islands, Pfaff explained.
“In these areas, warm ocean waters with a temperature of at least 80 degrees throughout a depth of 150 feet are more common,” he said.
The Gulf Stream can intensify weather, as it did with Isaias, which hit Ocean Isle Beach in August 2020, bringing with it 85-mile-per-hour winds, tornadoes and a 5-foot storm surge. It grew from a tropical storm into a category 1 hurricane in less than 24 hours prior to landfall.
“Tropical systems can undergo rapid development if conditions are favorable,” Pfaff said, pointing to other hurricanes, like Bill, which impacted the Western Caribbean in 2015, and Tomas, which struck the Windward Islands in 2010.
Hurricane Humberto in 2007 formed into a hurricane only 19 hours after becoming a tropical system. Warm water and convection fueled its intensification, which developed relatively close to where it made landfall in Texas.
Regionally, the last time a tropical storm formed this quickly and actually became a hurricane was with Gaston in 2004. It made landfall near Charleston and moved inland across central North Carolina.
“Otherwise, I don’t recall another specific to the Cape Fear region other than a few that developed much farther offshore,” said Pfaff, a resident of the area for 28 years.
Tropical Storm Colin — which brought 43 mile-per-hour winds and left behind up to 3 inches of rain in some areas — developed, hit and moved out within a 12-hour timespan. It didn’t threaten the area as more intense storms in the past and by Saturday evening was downgraded to a depression.
Pfaff said Colin formed in an area over warm water with weak wind shear over a developing cluster of thunderstorms, near a center of circulation. Tropical cyclones require weak shear overhead to progress.
“If they encounter strong wind shear aloft, the tops of the thunderstorms become blown off and the pressure never drops,” Pfaff noted.
Colin’s impacts were low across land areas, as most of the stronger wind gusts associated with the storm were embedded in thunderstorms located miles offshore.
It was the third named storm in the 2022 hurricane season, one the National Oceanic and Atmospheric Administration forecasts to be “above normal.” In an average year, there are usually around 14 named storms, seven hurricanes, and three major hurricanes. 2022 is expected to have 21 named storms, up to 10 hurricanes, and up to six major hurricanes.
There are three major reasons why the number could be higher this year. One is the favorable El Nino Southern Oscillation phase, which basically equates to less wind shear over the Atlantic Basin.
Above-normal sea temperatures also are a contributing factor. According to the EPA, the temperature of the sea’s surface has risen from 1901 to 2020 on average of 0.14 degrees per decade, totaling 1.5 degrees in 100 years.
Finally, the West African monsoon season is projected to be more active than usual, with numerous tropical waves expected to move off the west coast of Africa and into the tropical Atlantic waters.
However, seasonal outlooks are not impact forecasts, Pfaff reminds.
“Ultimately, all it takes is one storm to define a hurricane season,” he said. “People should not be fixated on the numbers, especially given our area’s history. We need to prepare the same way regardless of the seasonal outlook. For instance, in 1992 there were only seven named storms, but Andrew became a major hurricane with devastating impacts for south Florida.”
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