The Caribbean and the north Atlantic Ocean will see the greatest intensity of activity with the formation of three to six new hurricanes per season.
US long-range forecasters from NOAA and the Colorado State University said in their official outlook on Friday that the 2011 season will see seven to 11 tropical storms. Five to nine of them will become hurricanes (storms with winds above 74mph) with three to six becoming Category 3 hurricanes (category 3 hurricanes have winds over 110mph). The National Hurricane Center (NHC) has warned that severe weather across the east coast of the US and in the Gulf of Mexico is likely.
The northern North Atlantic is predicted to be quieter with three to five named storms. Tropical cyclones generally form further to the east, but the frequency has been increasing in the Atlantic basin. There are 25 named storms in a typical Atlantic hurricane season. Some storms may become hurricanes when they approach major land masses such as the Florida Keys or the Bahamas, but they are not considered a hurricane until a category 4 hurricane is onshore.
There has been a slight reduction in the intensity of tropical storms and hurricanes compared with the long-term average in recent years. This decrease has also been supported by increases in the number of storm-energy hours. Atmospheric conditions that encourage intense storms are more pronounced in the north Atlantic, tropical Atlantic and southern Indian Ocean than in the Caribbean Sea and eastern North Pacific.
The NHC continues to expect Atlantic sea surface temperatures to be near or above average, which could cause some tropical systems to strengthen as they move over warm surface waters.