An observational study of the influence of the Great Lakes on the speed and intensity of passing cyclones

Case studies have shown that the Great Lakes can intensify and alter the speed of passing cyclones in winter by contributing latent and sensible heat to the storms. However, the influence of the Great Lakes on cyclones has not been systematically examined using an extensive dataset. In this research, a National Climate Data Center dataset for the period 1965-90 was used to examine the rate of movement and change in mean sea level pressure of 583 cyclones as they passed over the Great Lakes. The Great Lakes had a strong effect on the passing cyclones during the ice-free/unstable season from September through November. As cyclones approached the lakes during this season, they accelerated. Once in the Great Lakes region, their rate of intensification increased (the change in pressure tendency at the center of the cyclone was negative). The acceleration into the region was less for cyclones during the ice-cover/unstable season, and rates of intensification for these cyclones did not change within the region. Cyclones that traversed the Great Lakes region during the stable season from May through July exhibited essentially the same behavior as those in the ice-free/unstable season. The authors' results for the unstable seasons (ice free and ice cover) are consistent with previous modeling case studies of the influence of the Great Lakes on passing cyclones. Because the lakes are generally cooler than the overriding air during spring and summer, a satisfactory explanation for the influence of the Great Lakes on cyclones during the stable season is not apparent.