Forecasters expect a significant rise in the number and strength of hurricanes likely to form in the Atlantic basin over the next several weeks.
Although a developing El Niño in the Pacific Ocean could shorten the season by hampering hurricane development, the tropics likely will remain very active until El Niño kicks in, forecasters said.
That could take weeks.
Hurricane forecasters, who had predicted nine to 12 storms, now expect anywhere from 12 to 17 named storms to form before the season ends in November. Of those, as many as eight could turn into hurricanes, with two or three major storms packing winds of at least 111 mph, officials said.
A storm that size could pose major problems for the Republican National Convention, Aug. 27-30 in Tampa. Organizers have said they're prepared for inclement weather and the Secret Service would evaluate storms on a case-by-case basis.
"We're focusing on having a successful convention, while making sure that the 50,000 people we're bringing are safe," RNC spokesman James Davis said. "But there are certainly things that are out of our control."
Forecasters changed the seasonal outlook because of low wind shear and warmer sea surface temperatures in much of the Atlantic basin — the Atlantic Ocean, Caribbean Sea and Gulf of Mexico. Sea surface temperatures in some areas are a degree or two above average.
Six storms have already formed this season, which got off to an early start with four named storms in June, a first since the National Hurricane Center began keeping records in 1851.
"When you get activity like this early in the season, it indicates conditions are extremely conducive for more activity," said Gerry Bell, lead hurricane forecaster at the Climate Prediction Center. "Warmer waters fuel hurricanes."
But hurricane formation could be hampered by El Niño, the shift of warm surface waters from the western Pacific Ocean to the eastern Pacific, creating high wind shear in the region where many hurricanes take shape.
"Once El Niño kicks in, we might see a quieter end to the hurricane season than we've seen in years," said Mike Halpert, the climate center's deputy director. "I don't think it'll play much of a role over the next month at least."
That might not be soon enough to affect hurricane season's most active period, when storms form in waters off the African coast and intensify as they travel across the Atlantic.
At least four tropical systems were active Thursday.
Tropical Storm Ernesto made landfall Thursday near the port city of Coatzacoalcos, Mexico, killing two people.
The system once known as Tropical Storm Florence, north of the islands of the east Caribbean, has been sheared and is not expected to develop further.
A tropical depression halfway between the Cape Verde Islands and the Lesser Antilles was moving west at 15 mph, according to the hurricane center. If it becomes a tropical storm, it would be named Gordon.
A fourth system moving off the African coast has a 20 percent chance of developing into a tropical storm within the next 48 hours, forecasters said.
Marissa Lang can be reached at firstname.lastname@example.org or (727) 893-8804.