The Atlantic hurricane season will be less active than usual, producing six to 11 named storms through Nov. 30, as moderate sea-surface temperatures and an El Niño weather pattern limit storm development, government forecasters said Wednesday.

Three to six of those storms may become hurricanes, with winds of at least 74 miles per hour, said Kathryn Sullivan, administrator of the U.S. National Oceanic and Atmospheric Administration. There may be as many as two major systems, which have 111 mph winds and are Category 3 or higher on the five-step Saffir-Simpson scale.

“Those ranges and averages are below average,” Sullivan said on a conference call with reporters. “Below average doesn’t mean that no pitches get thrown our way.”

The forecast falls short of the 30-year average of 12 named storms partly because an El Niño has developed in the equatorial Pacific, Sullivan said. The El Niño creates wind shear in the Atlantic, which tears apart the structure of hurricanes and tropical storms.

“El Niño suppresses the hurricane season mainly in the peak months of the season—August, September and October,” said Gerry Bell, lead seasonal hurricane forecaster at the U.S. Climate Prediction Center in College Park, Md.

Atlantic hurricanes are watched closely because they can be deadly, cause billions in property damage and, when they move into the Gulf of Mexico, disrupt oil and natural gas production and petroleum refining. The Gulf accounts for about 4 percent of U.S. natural gas production and 17 percent of oil output.

Storms in the eastern Pacific can threaten lives and property in Central America and Mexico.

Prediction Limits

While the forecast tries to predict the level of activity in the Atlantic, which has already produced one storm this year, it cannot say where those storms will strike, Sullivan said.

In 1992, the Atlantic produced six storms—including Andrew, which caused $26 billion in damage and contributed to the deaths of at least 65 people, the National Hurricane Center said.

The public shouldn’t focus too much on whether the seasonal prediction turns out to be completely accurate, said Joe Nimmich, deputy administrator of the Federal Emergency Management Agency. The forecast is the best information that scientists have about the storm season.

People should have a plan on how they will deal with an emergency, which includes an evacuation route, a way to contact family and friends, and the resources to deal with being isolated and without power for at least 72 hours, Nimmich said.

“What the predictions will give you is a good sense of the risk you face,” he said.