Storms typically don’t develop outside the hurricane season which starts June 1 and goes through the end of November but when they do develop, in May, the east coast of Florida is a real hot-spot.
Excluding 2014, there has been at least one named tropical system during May, most of which are east of Florida, in every year since 2012.
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For instance, take just last year, when Subtropical Storm Andrea formed on May 20 well east of the Bahamas.
Tropical Storm Arthur formed near the same location Tropical Storm Bonnie developed in 2016.
Before this in 2012, Tropical Storm Beryl developed in a similar area to the east of Florida before running into northern Florida.
All but two tropical cyclones over the last 20 years have been east of Jacksonville and even Tropical Storm Barry in the Gulf passed right over the First Coast.
All these May systems are weaker than storms later in the season and most have something in common which is the tendency to develop over the warm water flowing by the Gulf Stream.
Cold fronts sliding into Florida dissipate. Thunderstorms left behind take advantage of the only warm water available which is typically not in the Gulf this time of the year but along the east coast gulf stream.
Many times those thunderstorms combine with upper-level cold air building into a blend between a northern winter storm and a warm core tropical storm. These subtropical storms are hybrid systems most common at the start and end of hurricane season, before the water fully warms and when upper level winds lend a hand to growth.