Many people like the feeling of the gentle wind in spring. Many people like to see the falling leaves dancing in the wind in autumn. But sometimes, when the wind becomes a storm, it can be very destructive (毁灭性的)．

　　Every year, major storms cause many problems around the world. There is nothing people can do to stop these powerful forces of nature. But new techniques are helping scientists to predict (预测) how, when, and where big storms will happen. The more exact scientists' warnings are, the better people can prepare for the storms.

　　Predictions are improving. "We've gotten better over the years, especially the last few years，" says Phil Klotzbach, a scientist at an American university. How is a storm formed? Even if scientists know where a storm will happen, winds can suddenly change, carrying the

　　storm to a new direction. "For a hurricane to happen, conditions have to be just right，" Klotzbach says.

　　First, the ocean water needs to be warm enough so that it evaporates (蒸发) and rises into the air. As it rises, the vapor cools and turns back into liquid. This process gives off heat. This produces energy like an engine that causes winds to increase. It drives the formation of a hurricane.

　　If wind speed reaches 40 miles per hour, the system is called "tropical storm"， and it gets a name. At 75 miles per hour, it becomes a hurricane.

The hurricane season lasts from June to November. Ninety percent of all hurricanes hit in August, September, and October.