document: Based on the new findings , Mr. Gray predicted earlier this summer that the 1990 tropical storm season would be above average , and so far he seems to be right . In July he said there would be 11 storms severe enough to be named , of which six would be hurricanes . The National Hurricane Center said that as of yesterday there have been nine named storms this year , including four hurricanes , a higher rate than normal . Weather researchers have been seeking to predict hurricane patterns more accurately as an early warning for coastal residents of the U.S. and the Caribbean . A sharp decrease in hurricane activity over the past two decades spurred business and residential development that would be vulnerable to increased hurricane activity . Mr. Gray said the West African Sahel region is the newest of five indicators he uses to predict global hurricane activity . Atlantic hurricanes form from especially strong tropical storms that are triggered by winds and other air disturbances that sweep across Africa . Wind moving across warm ocean air causes powerful updrafts of air bearing sea water that eventually turn into rainclouds . Mr. Gray said he believes that in the absence of moisture , these storms quickly dissipate , but that the storms gather strength with additional moisture . Mr. Gray said his research , published in the current issue of Science , suggests that `` intense Caribbean hurricanes Gilbert , Joan and Hugo of 1988 and 1989 may be the forerunners of this change . '' Comparing year-to-year rainfall levels in the Sahel with the number of high-powered Atlantic hurricanes , Mr. Gray found a striking correlation . From 1947 to 1969 , for instance , rainfall in the western Sahel was especially abundant , and during this time there were 13 severe hurricanes that formed in the Atlantic Ocean . From 1970 to 1988 , the Sahel suffered through a terrible drought , and hurricane activity was unusually low ; only one severe hurricane , Gloria in 1985 , formed in the area . Mr. Gray searched back in recent history and found that the Sahel , which includes parts of Senegal , Mauritania , Mali and Gambia , goes through long periods of alternating dry and wet weather . He found that the Sahel was especially wet from 1870 to 1900 and from 1915 to 1935 . Hurricane activity was much higher during this time than during intervals when the Sahel was dry . Mr. Gray predicted that , based on historical cycles , the Sahel is entering a wet period . He said the drought conditions ended in 1988 and 1989 . He based his 1990 storm forecast on the higher-than-normal rainfall in the Sahel in July . Mr. Gray said his research suggests that climate changes in the Sahel do n't result from global warming problems associated with environmental pollution but from natural weather cycles .
extractive_keyphrases: tropical storm season hurricane patterns coastal residents global hurricane activity national hurricane center west african sahel region atlantic hurricanes rainfall levels weather researchers
abstractive_keyphrases: mr. gray