Monsoon rains, critical to life in much of Africa, shift north and south with the seasons. They normally reach the Sahel from July to September and the southern part of the continent from February into April. Low-pressure centers moving west from the Sahel during the monsoon often serve as seed for tropical storms and hurricanes in the North Atlantic. Hurrell's work does not address the possible impact of increased rains in the Sahel on future Atlantic hurricane activity.
For their study, Hurrell and Hoerling examined output from computer models at NCAR, NASA, NOAA, the European Centre for Medium-Range Weather Forecasts, and France's National Center for Meteorological Research (CNRM).