By Tom Brown
MIAMI (Reuters) - The 2013 Atlantic hurricane season could be "extremely active" and spawn 13 to 20 tropical storms, seven to 11 of which are expected to become hurricanes, the U.S. government's top climate agency predicted on Thursday.
Three to six of the hurricanes could become major at Category 3 or above, with winds of more than 110 miles per hour, the National Oceanic and Atmospheric Administration said in its annual forecast.
"For the six-month hurricane season which will start June 1, NOAA predicts an above-normal and possibly an extremely active hurricane season," said Kathryn Sullivan, the acting administrator of the agency.
Speaking at NOAA's Climate Prediction Center, she said the hurricane season for the Atlantic Ocean, Caribbean Sea and Gulf of Mexico threatened "quite a lot of activity" due to a combination of several climate factors, including warmer-than-average temperatures in the tropical Atlantic and Caribbean.
The average Atlantic season brings 12 tropical storms with six hurricanes, including three major hurricanes.
"This year, oceanic and atmospheric conditions in the Atlantic basin are expected to produce more and stronger hurricanes," said Gerry Bell, lead seasonal hurricane forecaster with NOAA's Climate Prediction Center.
"These conditions include weaker wind shear, warmer Atlantic waters and conducive wind patterns coming from Africa," he said.
The 2012 Atlantic season produced 19 tropical storms, 10 of which became hurricanes and two became major hurricanes. It will be remembered most for Superstorm Sandy, which NOAA says caused more than 200 deaths and more than $50 billion in damage in the United States.
Apart from people living in hurricane danger zones, NOAA's pre-season annual forecast is closely watched by energy analysts and oil producers.
The Gulf of Mexico, which is frequently threatened by tropical cyclones, accounts for about 20 percent of U.S. oil production. At the same time, around 30 percent of U.S. natural gas processing capacity and 40 percent of the country's refining capacity is concentrated on the Gulf Coast.
NOAA has said the Atlantic basin is still in the midst of a multi-decade active period for hurricanes that began in 1995 and could last as long as 25 to 40 years. Since the latest period began, 70 percent of the Atlantic hurricane seasons have been above-average, including 2012.
Hurricanes feed on warm water and another climate factor that could add to above-average activity this year is the absence of El Nino, a warming of the tropical Pacific that bring wind conditions that can suppress Atlantic hurricanes.
The weather phenomenon, which usually develops in the late summer to early fall during the peak months of the season, is not expected to develop in 2013, NOAA said.
NOAA's seasonal forecast does not provide hurricane landfall predictions, or say how many storms will hit land and where they are likely to strike.
But in another closely watched seasonal forecast, researchers at Colorado State University said last month that the odds of the United States being hit by a major hurricane were about 70 percent greater than predicted last year.
That forecast predicted that 18 tropical storms would develop in 2013, with nine expected to become hurricanes.
(Editing by Doina Chiacu)