(USA TODAY) - Top forecasters predict an above-average 2013 Atlantic hurricane season, with 18 tropical storms forecast, of which nine will be hurricanes.
A typical year, based on weather records that go back to 1950, has 12 tropical storms, of which seven are hurricanes. A tropical storm has sustained winds of 39 mph; it becomes a hurricane when its winds reach 74 mph.
The forecast was released Wednesday morning by meteorologists Philip Klotzbach and William Gray at Colorado State University's Tropical Meteorology Project. The Atlantic hurricane season starts June 1 and lasts until Nov. 30.
Gray's team was the first organization to issue seasonal hurricane forecasts back in 1984; this is the team's 30th seasonal hurricane forecast.
The team's forecast in 2012 -- 10 named storms and four hurricanes -- was far below what actually occurred: Last year, 19 storms formed, including 10 hurricanes. This included Hurricane Sandy, which slammed the Northeast coast in October, killing dozens and leading to billions of dollars in damage. Three straight Atlantic hurricane seasons have had 19 storms.
This forecast is for the Atlantic basin, which includes the Caribbean Sea and the Gulf of Mexico. Klotzbach said that of the nine predicted hurricanes, four should be major hurricanes - categories 3, 4 or 5 - with sustained wind speeds of 111 mph or greater.
"The tropical Atlantic has anomalously warmed over the past several months, and it appears that the chances of an El Nino event this summer and fall are unlikely," said Klotzbach. "Typically, El Nino is associated with stronger vertical shear across the tropical Atlantic, creating conditions less conducive for storm formation."
The Colorado State team's seasonal forecasts tend to be conservative: Since 2000, the team has underforecast the number of named tropical storms and hurricanes seven times, overforecast three times and been almost right - within two storms - three times, a USA TODAY analysis shows.
Insurance companies, emergency managers and the news media use the forecasts from Colorado State to prepare Americans for the season's likely hurricane threat. The team's annual predictions are intended to provide a best estimate of activity to be experienced during the upcoming season, not an exact measure, according to Colorado State.
For the entire U.S. coastline, there is a 72% chance of a major hurricane making landfall in 2013. The long-term average for that is 52%.
Colorado State's team will issue another seasonal forecast update on June 3, with additional updates released as the hurricane season progresses.
Earlier this week, the Weather Channel made its seasonal hurricane prediction: 16 named storms, of which nine will be hurricanes, of which five will be major hurricanes. The National Oceanic and Atmospheric Administration will be issuing its hurricane forecast in May.
The first named storms of the Atlantic hurricane season, which begins June 1, will be Andrea, Barry, Chantal, Dorian and Erin.
The eastern Pacific hurricane season starts May 15. Eastern Pacific hurricanes seldom have any impact on the USA, but can hit the west coast of Mexico.