The 2023 Atlantic hurricane season, which ends Nov. 30, has been so active we’ve almost run out of letters in the alphabet to name storms, hitting “T” last week when Tammy formed.
That means there have been 19 tropical storms or hurricanes this year, with V and W being the only letters left. (The National Hurricane Center skips the letters Q, U, X, Y and Z).
Climatologist Brian McNoldy, of the University of Miami, said 2023 has been an impressive year. “By any measure, this has been an above-average year — the number of storms, the accumulated cyclone energy, how long storms lasted, the number of named-storm days.”
Going beyond one round of the alphabet has only happened twice, in 2005 and 2020.
In 2005, there were 28 named storms, including the deadly Katrina, and 2020 produced 30.
Forecasters used the Greek alphabet as storm names, but now they simply start back at A with a new set of names.
The accumulated cyclone energy (ACE) that McNoldy mentioned is a “wind-energy index” that takes into account all of the named storms’ intensities and durations, giving the National Oceanic and Atmospheric Administration a total wind energy amount for the year.
The agency said it’s a more accurate measure of the season’s intensity than, say, the number of storms or the number of major hurricanes, which can be intense but short-lived.
The highest ACE in history was 1933. The second highest was 2005.
As of Wednesday, Oct. 25, 2023, the ACE was high — 127% of the historical average for that point in the season.
“Even if all the activity ended right now, the season would still be historically fairly impressive,” McNoldy said.
2023 is already at 116% of the average for a total season, and we’re only about 80% complete.
Though the season has been above average, there has only been one U.S. hurricane landfall, Idalia in Florida’s Big Bend region on Sept. 1.
Idalia then traveled through Georgia as a hurricane and South Carolina as a tropical storm. Two other tropical storms made U.S. landfall: Harold in Texas, and Ophelia in North Carolina.
In May, NOAA forecasters with the Climate Prediction Center called for a “near-normal” hurricane season, which meant a 40% chance of a near-normal season, a 30% chance of an above-normal season and a 30% chance of a below-normal season.
They called for a range of 12 to 17 total named storms (winds of 39 mph or higher).
We had 12 by Sept. 5, when Tropical Storm Lee formed.
Lee would become a Category 5 storm briefly, well east of the Caribbean, and weaken before making its way to Canada.
NOAA called for five to nine hurricanes. This week’s Tammy makes seven.
We’ve got five weeks to go.
They called for one to four major hurricanes (Category 3, 4 or 5) and we’ve had three: Franklin, Idalia and Lee.
Franklin made landfall in the Dominican Republic as a tropical storm, and later ramped up.
Idalia peaked as a Category 4 storm with maximum sustained wind speeds of 130 mph, but weakened to Category 3 before making landfall.
NOAA’s outlook changed once the season got underway.
“The Atlantic Ocean was hitting record-warm water temperatures,” McNoldy said, “so that gave the season a boost.”
NOAA then revised their outlook on Aug. 10 to an “above-normal” year.
“Forecasters believe that current ocean and atmospheric conditions, such as record-warm Atlantic sea surface temperatures, are likely to counterbalance the usually limiting atmospheric conditions associated with the ongoing El Niño event,” said the report.
The water temperature factor played out but El Niño, which can cause storm-toppling wind shear in the Atlantic, did not.
A saving grace was a weak semi-permanent, high-pressure system over the Atlantic known as the Bermuda High.
Hurricanes travel along its southern edge and shoot north once they reach its western end.
When it’s strong and shifted closer to the U.S., it guides storms on a collision course with the east coast of the U.S., or into the Gulf of Mexico.
“A weaker subtropical high (Bermuda High) was a big player,” McNoldy said. “A lot of storms turned north well before reaching the U.S.”
As for the Atlantic’s record-high water temperatures, McNoldy said “sea surface temperatures play a role in ACE, though indirectly. We’re more likely to see stronger and longer-lived storms with a warmer ocean, but there are other ingredients that govern a season’s activity, too.
“This year had the warmest sea-surface temperatures on record, but it was far from the most active season on record.”
As for the rest of the season, “October can be fairly active, and we look to the Caribbean for that,” McNoldy said. “November is usually quiet, but it’s not over.”
Last year’s Hurricane Nicole zigzagged north of the Bahamas and hit Vero Beach on Nov. 10.
“There’s still some model interest in the western Caribbean,” McNoldy said. “Those storms usually move north into Florida. We’ll see.”
If they do, we’ll get to know Vince and Whitney.
