(Bloomberg) -- The Atlantic should produce anear-normal 12 storms during thesix-month hurricane season that officially begins Wednesday, whilethe U.S. coastline has a below-average chance of being struck by amajor system, according to Colorado State University’sforecast.

Of the 12 storms, five could become hurricanes and two couldgrow into major systems of Category 3 or stronger, said Phil Klotzbach, lead author of the closely watchedseasonal outlook. The U.S. has a 50% chance of being struck by amajor hurricane, just below the 20th century average of 52%.

“As is the case with all hurricane seasons, coastal residentsare reminded that it only takes one hurricane making landfall tomake it an active season for them,” Klotzbach wrote in hisforecast. “They should prepare the same for every season,regardless how much activity is predicted. ”

In an average year, 12 systems of tropical storm strength orgreater form from June 1 through Nov. 30. Already this year,Hurricane Alex formed in January and Tropical Storm Bonnie struck the coast ofSouth Carolina last week.

Klotzbach said his prediction doesn’t include those two, so 2016could end up with 14 in total. A weakening El Niño in thePacific Ocean could make conditions in the Atlantic more conducivefor tropical storms and hurricanes.

Storms’ cost

Atlantic hurricanes can exact a high toll in human life, causebillions of dollars in property damage and roil energy andagriculture markets.

About 5% of the U.S. marketed natural gas production comes fromthe Gulf of Mexico, along with 17% of crude oil, Energy InformationAdministration data show. The Gulf region also is home to more than45% of petroleum refining capacity and 51% of gas processing.

Florida, a frequent target of storms, is the world’ssecond-largest orange-juice producer, behind Brazil. More than 6.6million homes with an estimated reconstruction cost of $1.5trillion lie in vulnerable areas along the Atlantic and Gulfcoasts, according to the Insurance InformationInstitute in New York.

El Niño

Among the weather changes wrought by El Niño is a greaterchance of wind shear across the Atlantic that can tear stormsapart. If the Pacific phenomenon fades, wind shear in the Atlanticwill also drop away.

However, water temperatures in the far northern Atlantic, aswell as in the sub-tropical areas of the northeastern part of thebasin, are cooler than normal, Klotzbach said. This could indicatea larger shift in what is known as the Atlantic MultidecadalOscillation, or AMO, to a cooler phase.

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The Atlantic tends to produce fewer storms when the AMO is inits cooler phase, which can last for 20 to 40 years. The oceanshifted to its warm phase in 1995 and most of the hurricane seasonssince then have produced more than the average of 12 storms a year;2005 spawned a record 28 storms.

Wilma’s record

Among those storms was Katrina, which wrecked New Orleans and thecentral Gulf Coast, and Wilma, the last major hurricane, with windsof 111 miles (179 kilometers) per hour or more, to hit the U.S. Thenearly 11 years since Wilma is the longest the country has gonewithout being struck by a major system.

Last week, the National Oceanic and Atmospheric Administrationalso predicted the Atlantic would have a near-normal season, forthe same reasons cited by Klotzbach. NOAA called for 10 to 16 namedstorms, with four to eight becoming hurricanes and one to fourbecoming major systems. There were 11 named storms last year andeight in 2014.

In April, Klotzbach also called for 12 storms, five hurricanesand two major systems. That forecast was released just daysbefore the death of Klotzbach’s mentor,William Gray, the originator of tropical seasonaloutlooks.

“He promised me when I saw him a few days before his death thatI would give him at least 50 more years of seasonal forecasts,”Klotzbach wrote in the current outlook. “I will do my best tocontinue his legacy and produce seasonal Atlantic hurricaneforecasts for as long as I can.”

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