A pathetic clump of swirling clouds and weak thunderstorms shamefully churning off the coast of South Carolina became Subtropical Storm Ana last night. The storm is the first tropical cyclone we’ve seen in May since Alberto in 2012, and the earliest in the year since Ana (no relation) in 2003.

Welcome to May! We are now two-thirds of the way through spring, and right on schedule, the atmosphere has a mini heat wave in the forecast for most of us east of the Rockies. On top of that, models are trying to spin up some sort of a tropical cyclone-ish thing off the East Coast next week.

In a rare move yesterday, the Brazilian Navy's weather division declared a swirling storm off the southeastern coast of Brazil (near São Paulo) a subtropical storm named Bapo. Tropical and subtropical cyclones in the South Atlantic Ocean are relatively rare, with only a hundred or so recorded in the past sixty years.

Another day, another explainable weather event. Subtropical Storm Fay is on the cusp of developing in the Atlantic Ocean, and it's likely going to brush Bermuda in a few days. What is a "subtropical storm" and why is it different from a regular ol' tropical storm?