Two main factors shaped this year’s forecast. One is the presence of a weak El Niño pattern in the Pacific, which tends to increase wind shear and suppress storm formation; some researchers, including Dr. Klotzbach, had suggested that this would cause the season to have somewhat fewer storms than normal . But there are also predictions of conditions that favor more storm activity, which include warmer-than-average temperatures in the tropical Atlantic Ocean, said Neil Jacobs, acting administrator of the National Oceanic and Atmospheric Administration.

The problem with announcements that try to forecast storm activity , some climate scientists say, is that they tell people what the government can best predict, but don’t give them the information they need most: Will damaging storms hit the coast? “It doesn’t say anything about how many are going to make landfall,” said Suzana J. Camargo, a research professor at the Lamont-Doherty Earth Observatory and executive director of the Initiative on Extreme Weather and Climate at Columbia University. Researchers are trying to come up with more regionally focused forecasts, she said, but that is “a harder problem.”

That means that the annual announcement of forecasters’ expectations for the coming season can be “inadvertently misleading,” said Kerry Emanuel, an atmospheric scientist at the Massachusetts Institute of Technology. “People interpret it as a measure of risk for themselves.” A single powerful storm striking land can be devastating, even in a quiet season, but with the announcement of a quiet season “people let their guard down.” For example, 1992 saw relatively few storms, but one of them was Andrew, which caused extensive damage in Florida and Louisiana and was the most costly hurricane on record until Katrina in 2005.

This year’s hurricane season comes during a period of extreme weather across much of the United States, with extensive flooding in the Midwest and along much of the Mississippi River. Violent storms in the Southern Plains have spawned numerous tornadoes.

While the connections between climate change and tornadoes are not straightforward, the connections to heavy rainfall and to the tendency of some weather patterns to stall are becoming clearer. Jennifer Francis, an atmospheric scientist at the Woods Hole Research Center, said recent persistent late-season California rains, the profusion of storms and flooding in the Midwest, and heat waves in the southeast are associated with atmospheric patterns that cause weather systems to sit instead of move across the country.