Forecasters expect near-normal tropical storm season in Atlantic

MIAMI — U.S. government forecasters expect a near-normal Atlantic hurricane season, after three relatively slow years. But they also say climate conditions that influence storm development are making it difficult to predict how many hurricanes and tropical storms will arise over the next six months.

The National Oceanic and Atmospheric Administration’s outlook Friday called for a near-normal season with 10 to 16 named storms, with four to eight hurricanes and one to four “major” ones with winds reaching 111 mph and up.

The long-term season averages are 12 named storms, with six hurricanes and three major ones.

The Atlantic hurricane season officially starts June 1, but tropical weather got a head-start this year: Hurricane Alex made an unseasonable debut in January over the far eastern Atlantic.

On Friday, the National Hurricane Center said an area of low pressure between Bermuda and the Bahamas became a tropical depression. A tropical storm warning was issued for the South Carolina coast.

Hurricane hunter aircraft were investigating the disturbance, and communities along the coasts of Georgia and the Carolinas should monitor its development, said NOAA Administrator Kathryn Sullivan.

While they can’t predict whether any storm will strike the U.S., NOAA officials said significant variables are at play.

It’s unclear whether a decades-long high-activity era for Atlantic hurricanes has ended, said Gerry Bell, lead seasonal hurricane forecaster with NOAA’s Climate Prediction Center. Meanwhile, El Nino is dissipating while La Nina looms for the season’s peak from August through October.

El Nino is the natural warming of parts of the Pacific Ocean that changes weather worldwide. That tends to reduce hurricane activity in the Atlantic, while La Nina tends to increase it.

The active storm era associated with warm Atlantic temperatures and stronger West African monsoons began in 1995, but recent hurricane seasons showed shifts toward a cooler phase marked by colder waters and a weaker monsoon, Mr. Bell said.

The 2015 season was slightly below average with 11 named storms, including two tropical storms that made landfall and caused flooding in South Carolina and Texas. Hurricane Joaquin, one of two storms to reach major hurricane strength, killed all 33 mariners aboard a cargo ship that sank off the Bahamas in October.

The last major hurricane to strike the U.S. mainland was Hurricane Wilma, which cut across Florida in 2005. Wind speeds determine whether a hurricane is classified as “major” — Category 3 and up on the hurricane wind scale.