The National Oceanic and Atmospheric Administration slightly lowered the outlook it released in May, but an above-normal season was still expected, said Gerry Bell, lead seasonal hurricane forecaster at NOAA's Climate Prediction Center in Washington.
The updated forecast calls for 14 to 20 named tropical storms, down from a range of 14 to 23. The hurricane season started June 1 and ends Nov. 30, but the peak period for hurricanes runs from August through October.
Eight to 12 storms could become hurricanes, and four to six of those hurricanes could become major storms, blowing winds of 111 mph or more, forecasters said.
"August heralds the start of the most active phase of the Atlantic hurricane season and with the meteorological factors in place, now is the time for everyone living in hurricane prone areas to be prepared," NOAA Administrator Jane Lubchenco said in a statement.
Historically during active storm seasons, multiple hurricane strikes are much more likely for both the Gulf Coast and the East Coast in the U.S.
The Caribbean also sees a sharp increase in storm activity during such seasons, which is bad news for Haiti, where approximately 1.6 million people continue to live under tarps and tents nearly seven months after a catastrophic earthquake wrecked its capital.
Three named storms have developed since this hurricane season began. Hurricane Alex made landfall June 30 in northern Mexico. Tropical Storm Bonnie forced crews drilling a relief well in the Gulf of Mexico to evacuate last month but petered out.
Tropical Storm Colin dissipated Tuesday over the open Atlantic, but its remnants could strengthen again into a tropical storm, forecasters at the National Hurricane Center in Miami said Thursday.
The May outlook which called for eight to 14 hurricanes, with possibly three to seven major hurricanes reflected the possibility of even more storms forming in June and July than actually did, Bell said.
Bell said the update is based on conditions indicating a high-activity era that began in 1995 continues.
"The atmospheric and oceanic conditions now in place are very conducive to hurricane formation, as we had predicted in May," he said.
A Pacific Ocean phenomenon called La Nina developed in July, reducing wind shear in the Atlantic and making it easier for storms to take shape.
Ocean temperatures are exceptionally high, and the warmest since 2005 when Hurricanes Katrina and Rita ripped into the same part of the Gulf Coast now coping with one of the world's worst oil spills.
Historically, three named tropical storms will spin into the Gulf of Mexico between August and November during above-normal seasons, Bell said. Any impact on the oil remaining in the Gulf from an April 20 rig explosion off Louisiana would depend on a storm's strength and path across the water.
Tropical storms are named when sustained wind speeds reach 39 mph. They become hurricanes when sustained winds reach 74 mph. Major hurricanes blow at 111 mph or more. The strongest hurricanes are labeled Category 5, with winds greater than 155 mph.
Three hurricanes developed out of nine tropical storms in 2009. None of the hurricanes made landfall in the United States. Hurricane Ida hit Nicaragua as a Category 1 storm in November.
Colorado State University researchers said Wednesday they also expected this year's season to be more active than average with 10 hurricanes, five of them major.
Hurricane season ends Nov. 30.