We’re due for a big one, some say.

Every year now since 2004 and 2005 — the years of Hurricanes Ivan, Dennis and Katrina — the Gulf Coast has been "due" for a storm season worse than the year before.

Now, one month into the official hurricane season, forecasters expect a double-digit number of storms to develop.

As many as 13 to 20 named systems — storms with 39 mph winds or higher — are estimated for the coast by the National Oceanic Atmospheric Administration this year.

Three to six of those may be major hurricanes, categories three or higher.

If those numbers sound familiar, that’s because weather experts have been predicting more active weather patterns since the mid-1990s, said Bill Williams, director of the Coastal Research Center of the University of South Alabama.

Yet, forecasting storm intensity remains a more elusive challenge.

That’s why you see so much leeway in the number of major storms predicted, Williams said.

"It’s a real problem."

The factors that determine how strong a storm will be and where it will make landfall rests on shaky science. And the years between major storms offers a premature glimpse into storm outlook for the season.

"Historically, every 10 years or so we’ve had a major storm," said Jeff Garmon, meteorologist of the National Weather Service in Mobile. "Unfortunately, nature is not as predictable as that."

Weather experts look to a number of ingredients that combine to make an intense tropical storm.

Wind shear and surface water temperatures are among the top factors, If not the most important indicators used, Garmon said.

The rapid change in wind speed and direction that can shear off the intensity of a hurricane and warm waters can also increase it.

Sometimes el nino occurs, when the Pacific Ocean warms up and wind blows from west to east, weakening hurricanes for a short period.

Not this year, which helps explain the double-digit amount of storms expected.

Among the lessons learned from Hurricane Katrina is the importance of preparation. With winds as high as 125 mph, Katrina made landfall, leaving behind a wrecked Gulf Coast. And the storm seasons since 2004 and 2005 have not yielded a major storm of its size or intensity.

"Just because you have a minimal year," Williams said, cautioning residents, "it doesn’t mean you are safe from a big storm."

Last year, only one major hurricane made landfall — Superstorm Sandy.

Forecasters say the number of tropical cyclones predicted this year does not mean each of them will reach land.

From the time storm systems form over the Atlantic, the Caribbean and the southern Gulf of Mexico there are a myriad of factors that influence where they go, Garmon said.

"Whether we [the Gulf Coast] get a system," he said, "is just the luck of the draw."

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