With four storms already in the books, the Atlantic is expected to produce a total of nine to 13 named storms during the six-month hurricane season that ends Nov. 30, the National Oceanic and Atmospheric Administration said.

That’s down from the 10 to 16 systems of tropical-storm strength or greater the agency that oversees the National Weather Service called for in May. Of the total announced Thursday, four to seven could become hurricanes, with only one, or perhaps even none, becoming a major system with winds of 111 miles per hour or more. A storm is named when winds reach at least 39 mph.

“All of these numbers are lower than we predicted in May,” Gerry Bell, hurricane forecaster with the U.S. Climate Prediction Center.

Hurricane season is closely watched by markets because about 5 percent of U.S. natural gas and 17 percent of crude comes out of the Gulf of Mexico, according to the U.S. Energy Information Administration. In addition, the hurricane-vulnerable coastline also accounts for 45 percent of U.S. refining capacity and 51 percent of gas processing.

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Florida is the world’s second-largest producer of orange juice. Along the Atlantic and Gulf coasts there are more than 6.6 million homes with an estimated reconstruction cost of $1.5 trillion, according to the Insurance Information Institute in New York.

Last year, three major hurricanes hit the U.S. — Harvey, Irma and Maria — helping drive total losses to more than $215 billion, according to Munich Re. It was the most costly season on record, surpassing 2005 which produced Katrina. Overall 17 named storms formed in 2017, which fell in line with NOAA’s prediction of 11 to 17.

This year has been unusually active in terms of the number of storms. On average, the Atlantic doesn’t see four named storms until Aug. 23. But those systems that have formed so far this year have either been small, weak or far from land. That’s largely due to cooler water across much of the Atlantic and dry air from Africa.

Forecasters are watching the Pacific, too. If an El Nino forms by next month, it could increase wind shear across the Atlantic, making it even harder for storms to take root. The U.S. Climate Prediction Center said there is a 51 percent chance an El Nino could be under way from August to October.

While the Atlantic season runs from June 1 to Nov. 30, the most active part starts about Aug. 20, building to a statistical peak on Sept. 10. Last week, Colorado State University called for a total of 12 storms by season’s end.