U.S. forecasters predicted Thursday that this year's Atlantic hurricane season would produce a normal number of about nine to 15 tropical storms, with as many as four to eight of those becoming hurricanes.
The National Oceanic and Atmospheric Administration released its initial outlook for the six-month storm season that officially begins June 1. One to three storms could become major hurricanes with top winds of 111 mph (178 kph) or higher.
Though this season isn't expected to be as busy as last year's above-average season, federal officials warned coastal residents to start stocking up on hurricane supplies and forming evacuation plans anyway.
"That's still a lot of activity. So just because we're predicting a near normal season doesn't mean anybody's off the hook at all," said Gerry Bell, the lead seasonal forecaster at NOAA's Climate Prediction Center.
Atmospheric and marine conditions indicating a high-activity era that began in 1995 for Atlantic hurricanes continue, Bell said.
However, the weather phenomenon known as El Nino, which warms Pacific waters near the equator and increases wind shear over the Atlantic, may develop by the late summer or early fall and help suppress storm development.
"Our range (of expected storms) is a bit wider this year because of this inherent uncertainty right now based on the best guidance we have as to whether El Nino will form or not," Bell said.
This season got an early start when Tropical Storm Alberto formed Saturday off the coast of South Carolina. Alberto dissipated Tuesday over the Atlantic.
Alberto was unusual for being a small storm that formed in a small area favorable for storm development, but the weather conditions as spring transitions into summer sometimes produce tropical systems, said Bill Read, director of the National Hurricane Center.
Forecasters name tropical storms when their top winds reach 39 mph; hurricanes have maximum winds of at least 74 mph. The next named storm will be named Beryl.
No major hurricane has made a U.S. landfall in the last six years, since Hurricane Wilma cut across South Florida in 2005. This August will mark the 20th anniversary of Hurricane Andrew's catastrophic landfall in South Florida as a Category 5 storm. The season that spawned Andrew started late and produced a total of just six named storms.
"It takes one storm to come ashore, regardless of the intensity of the season, to create a disaster," said Federal Emergency Management Agency's deputy administrator for protection and national preparedness, Tim Manning.
The seasonal average is 11 named storms, six hurricanes and two major hurricanes. The 2011 hurricane season, one of the busiest on record with 19 named storms, produced Irene, one of the costliest storms in U.S. history.
Irene killed at least 47 in the U.S. and at least eight more in the Caribbean and Canada as it followed a rare path up the Eastern seaboard from North Carolina, across the Mid-Atlantic and near New York City.
Flooding from the storm was the most destructive event to hit Vermont in almost a century, killing six people and leaving hundreds homeless while damaging or destroying hundreds of miles of roads, scores of bridges and hundreds of homes. About a dozen communities were cut off for days, requiring supplies brought by National Guard helicopters.
Read said forecasters are trying to apply lessons learned from Irene's destruction to their storm preparedness message this year.
"We think we were conveying, especially in western New England and upstate New York, meteorologically and hydrologically, what we thought was going to happen up there," Read said. "It was one of the better forecasts I've seen, in 40 years of doing this, on rainfall for a land falling hurricane."
Many in New England contend, though, that Irene's flooding caught them by surprise. Fixing the communications gap remains a challenge for forecasters, Read said.
Hurricane season ends Nov. 30, and the peak period for hurricane activity runs from August through October.
NOAA's National Hurricane Center: http://www.hurricanes.gov