While not officially part of Atlantic hurricane season, May has seen plenty of tropical cyclones over the years. According to NOAA, the month of May has seen a total of 22 tropical storms and four hurricanes since reliable records began in 1851, making it the most active month outside of the official seasonal bounds of June 1 to November 30. Based on these data, on average, an Atlantic tropical cyclone forms in May about once every ten years. This total does not include subtropical storms. It is worth nothing that six of the last ten years have had a tropical or subtropical cyclone form in May. Of these, five of six formed in the subtropical western Atlantic Ocean, and none of them have reached hurricane strength.

Last season, we had Tropical Storm Bonnie in late May, which brought moderate rainfall to the Carolinas Memorial Day Weekend. A year earlier, Tropical Storm Ana became the earliest tropical cyclone to make landfall in the United States in recorded history, making landfall near the North Carolina-South Carolina border on Mother’s Day.  These May Southeastern U.S. storms usually form when a ridge of high pressure forms over the Northeastern United States, and an area of low pressure forms east of the Bahamas underneath, eventually consolidating into a tropical cyclone and moving northwestward. In rare cases, May activity has occurred in the Caribbean as well, such as in 2008 with Tropical Storm Arthur on May 31.

It will be interesting to see if the recent uptick in May Atlantic tropical cyclone activity continues, but it could just be an unusual period of coincidence. If May activity continues, the National Hurricane Center may have to consider extending Atlantic hurricane season to May 15. Personally, I feel as if the season should be extended to May 15 to match with the East Pacific basin and to account for the recent increase in May activity.  The National Hurricane Center has previously said that they do not intend to extend the season, because they do not feel ten years is a large enough sample size to warrant extending the season, and this is understandable.

I am also starting to see the some hints of late May Caribbean tropical development on the GFS model. However, since it remains over a week out and other models such as the ECMWF and CMC do not show development as of this writing, I have decided not to write a full post on it yet. I’ll be back tomorrow with another blog, possibly about the Caribbean system if more models begin to pick up on it.