Last week Tropical Storm Andrea sprung to life in the eastern Gulf of Mexico and brought flooding rains and some tornadoes to Florida and the east coast of the United States. As the picture above shows, Andrea occurred in the “sweet spot” for June tropical cyclones based on the historical record dating back to 1851. That same long record shows that, on average, we see a May or June storm one out of two seasons. However, the past 20 years have been unusually active, with 15 out of the last 20 seasons having a tropical storm in May or June. Scientists have learned that we go through cycles lasting from 25 to 40 years of more than normal activity followed by less than normal activity. We are in the 20th year of the current active cycle. So I was thinking, maybe being in the active cycle can explain why we are having so many years with May or June storms. I looked at the records during the last active cycle, 1926 through 1969. During that active cycle there were 23 out of 43 seasons with a May or June storm, which is close to average.
I checked with some experts on seasonal aspects of hurricanes. Dr. Phil Klotzbach, who produces the Colorado State hurricane season forecast, thinks most likely it has something to do with the improvements in technology. I went back to the data from the previous active cycle and separated out the years 1945-1969 to account for the time when hurricane hunters routinely began flying the tropics. Sure enough, 15 of 24 seasons had a May or June storm during that period, which is closer to the frequency we are now experiencing. Dr. Phil also pointed out the improvements in satellite imagery since 1969 that allows for early detection and accurate diagnosis.
Dr. Jeff Masters of Wunderground posted a blog recently showing studies that hint that a consistently warmer Atlantic Ocean, including the Gulf and Caribbean may be contributing to a longer hurricane season, thus more storms in May and June. Makes sense as we know warm oceans contribute to the development of tropical cyclones.