As the American heartland continues to be hammered by a late but lethal tornado season, the U.S. East Coast is bracing for what could be another damaging and deadly hurricane season triggered by unusual climate conditions.
The 2013 Atlantic hurricane season, which officially begins Saturday, likely will be "above normal and possibly extremely active," according to officials at the National Oceanic and Atmospheric Administration.
Meteorologists say the confluence of warm tropical waters and the slim chance of a cyclone-suppressing El Niño event may fuel three to six major hurricanes over the course of the summer, less than a year after Superstorm Sandy ravaged the mid-Atlantic region. Major hurricanes are defined as Category 3 or above.
Sandy was downgraded from hurricane status to tropical storm status just before it battered the northeast U.S. last October.
Although meteorologists cannot say with certainty how many storms will hammer the coast – or where they will strike – there's a 96 percent chance of a hurricane hitting somewhere along the U.S. coast this summer, according to a forecast released in April.
"We really can't say where the storms are going to go," said Dr. Philip J. Klotzbach of the Tropical Meteorology Project at Colorado State University, who authored the forecast with his colleague Dr. William Gray. "But we know that more active seasons have more storms that make landfall."
Above-average sea-surface temperatures create an environment that "will be very conducive for waves to develop and intensify" and potentially generate associated phenomena, such as increased moisture and lower air pressure, that foment giant storms, according to Klotzbach.
Water temperatures are expected to be 0.8 degrees Fahrenheit warmer than usual, according to The Associated Press.
Although an uptick of less than one degree "doesn't seem like a heck of a lot," Klotzbach said, "it makes a big difference in tropical waters."
What's more, the unlikeliness of a significant El Niño event will make it easier for a cyclone to take shape, according to NOAA. El Niño is a vast stretch of unusually warm water in the Pacific Ocean that typically takes the edge off hurricanes.
"El Niño … is not expected to develop and suppress hurricane formation this hurricane season," said Kathryn Sullivan, acting NOAA administrator.
NOAA forecasts 13 to 20 tropical storms, seven to 11 of which are projected to become hurricanes and three to six of which are projected to become major hurricanes.
Klotzbach's projection of four major hurricanes is in that range.
The last major hurricane to make landfall in the U.S. was Wilma in 2005, according to Klotzbach. Since then, five Category 1 or 2 storms – defined by winds moving as fast as 100 mph – have struck the U.S.
Atlantic hurricane season typically lasts for six months, usually peaking between late August and mid-October.
In the introduction to their forecast, Klotzbach and Gray warn coastal residents to take precautions in advance of storm season.
"Coastal residents are reminded that it only takes one hurricane making landfall to make it an active season for them, and they need to prepare the same for every season, regardless of how much or how little activity is predicted," they wrote.