dr. radley horton is an expert on these super storms. he's a climate scientist at columbia university.he definition of a hurricane? very strong winds. it's a storm that forms over the warm waters of the tropical oceans, and as soon as that storm's winds get up to about 35 miles an hour, we call it a tropical storm. and if if its winds get up to 75 miles an hour, it's a hurricane. >> how are hurricanes classified? >> hurricanes are classified by how strong their winds are. a category 1 hurricane, which is the weakest, has winds just above 75 miles an hour. category 5, which is the strongest, is winds at around 150 miles an hour. >> so, what causes these hurricanes? >> hurricanes are caused by a combination of factors. several things have to come together for you to get a hurricane. one of the most important things hurricanes form over the warm waters of the tropics. with the warm sun beating down, when temperatures get to be about 80 degrees fahrenheit, conditions are right for a lot lot of power to hurricanes. >> have hurricanes become more common or stronger in recent years? >> we nee