A developing El Nino is forecast to suppress tropical storms and hurricanes this summer and fall, contributing to a below-normal storm season, U.S. forecasters said Thursday.

The National Oceanic and Atmospheric Administration predicts eight to 13 tropical storms will develop in the Atlantic this year, three to six of which will become hurricanes. One or two of those could intensify into what are considered "major" hurricanes.

Forecasters urged preparation despite the predictions of a below-average season, citing seasons like 1992, which came at the tail end of an El Nino and brought devastation to Florida with Hurricane Andrew. NOAA also stressed the risks of storm surge and unveiled plans to better communicate coastal flooding risks to the public.

"Any section of our coastline can be hit by a severe tropical storm, and one storm can wreak tremendous havoc," NOAA Administrator Kathryn Sullivan said during a conference call.

Hurricane season begins June 1 and typically peaks in the second half of August and first half of September, running through November. But with the global climate pattern known as El Nino forecast to set in by the end of summer or fall, half of the season or more could be marked by conditions unfavorable for tropical cyclone development, forecasters said.

For starters, El Nino is known to increase wind shear, when wind speeds vary in speed and direction at different altitudes. That "will either prevent a storm from forming or rip a hurricane apart," said Gerry Bell, lead seasonal hurricane forecaster at NOAA's Climate Prediction Center in College Park.

On top of that, ocean surface temperatures are forecast to be about average in the Atlantic this season, whereas they have trended higher in recent seasons, Bell said. Warmer waters mean more energy to strengthen storms.

But the Atlantic basin remains in the midst of a decades-long pattern of high tropical cyclone activity that began in 1995, he added. That trend, weighing against the likelihood of El Nino and cooler ocean temperatures, has prompted NOAA forecasters to suggest a 50 percent chance of a below-normal season, a 40 percent chance of a near-normal season and just a 10 percent chance of an above-normal season.

The NOAA outlook is similar to that of other hurricane forecasters — the Tropical Meteorology Project at Colorado State University predicted last month that nine named tropical storms and three hurricanes would form this season. AccuWeather.com released predictions Sunday of 10 tropical storms and five hurricanes.

In a normal season, there are a dozen named tropical storms — a designation for tropical cyclones with maximum wind speeds of at least 40 mph — and six or seven hurricanes.

With the absence of El Nino since May 2010, season forecasts have recently trended toward high activity, though not all the predictions came true. But overall, the tropics have been active over the past two decades, with 12 of the past 20 hurricane seasons more active than normal, Bell said.

In the 2013 Atlantic hurricane season, 14 named storms formed, but only two of them became hurricanes and none became major hurricanes, with wind speeds of at least 111 mph. That was below preseason predictions of as many as 18 to 20 named storms and eight or nine hurricanes.

Before that, the hurricane seasons of 2010, 2011 and 2012 all tied for third most active on record, with 19 tropical storms apiece.

To ensure better preparation for the flooding that storms can bring, NOAA officials emphasized Thursday they would add graphical forecasts of storm surge to regular updates on tropical storms' forecast tracks and intensity. They moved the annual news conference unveiling the hurricane season forecast for 2014 to New York City, drawing attention to the devastation storm surge caused there during Superstorm Sandy.

The storm surge forecasts will use a new forecasting model to show the depth, location and timing of coastal flooding.

sdance@baltsun.com

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