A Tropical Storm in April? It's Not Unheard Of

Jon Erdman
Published: April 20,2016

Visible satellite image of Subtropical Storm Ana taken by the OrbView-2 satellite on April 20, 2003. Ana would become a tropical storm on April 22.
(SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE)

The Atlantic hurricane season officially stretches from June through November. However, one tropical storm this century flared up in the Atlantic basin in April.
In 2003, Tropical Storm Ana became the only tropical storm on record to form in the Atlantic basin in April.
That early in the calendar, "April Ana" didn't form from a tropical wave of low pressure coming off west Africa. It instead formed as an area of low pressure aloft spinning near an old surface frontal boundary about 250 miles west of Bermuda.
(WEATHER 101: Where Hurricanes Come From)
Eventually, thunderstorms began clustering near the surface low, warming and moistening the low-mid levels of the atmosphere sufficiently enough for the National Hurricane Center to classify the storm as Subtropical Storm Ana during the late-night hours of April 20. (NHC post-analysis concluded this actually occurred over 18 hours earlier in the day.)
(WEATHER 101: What is a Subtropical Storm?)
Post-analysis of microwave satellite imagery estimated Ana became the first April Atlantic tropical storm of record when it exhibited enough consolidated thunderstorms near the center by early evening on April 20.
Dr. Rick Knabb, current director of the National Hurricane Center, goes into much greater detail on this process in the case of Hurricane Gustav in September 2002.

Track of Tropical Storm Ana in April 2003.

Despite a preliminary tropical storm warning issued for Bermuda, Ana remained far from land, tracking first toward the southeast, then generally east over the next several days, reaching its estimated maximum intensity of 60 mph peak sustained winds before merging with another frontal system between Portugal and the Azores on April 27.
(MORE: 2016 Hurricane Season Outlook)
But Ana was deadly, at least indirectly. Two people drowned after a boat capsized in high surf generated in part by Ana near Jupiter Inlet, Florida, according to the National Hurricane Center's final report.
While Ana remains the only April Atlantic tropical storm in records dating to 1851, an April 1992 subtropical storm was found in post-analysis by the National Hurricane Center.
Since it was not classified as such at the time, a later hurricane that year, Hurricane Andrew, got the "A" name in 1992.
Neal Dorst of NOAA's Atlantic Oceanographic and Meteorological Laboratory (AOML), says there is nothing magical about the June 1 start of the hurricane season. June through November was selected to capture 97 percent of Atlantic tropical cyclone activity.
There have been 19 Atlantic tropical/subtropical storms or hurricanes before June 1 in 17 different years from 1950-2015, for an average return interval of once every four years.
This most recently happened in May 2015, when another Tropical Storm Ana made landfall near Myrtle Beach, South Carolina.
(MORE: The Earliest U.S. Hurricane Landfalls)
Three years prior to that, both Tropical Storms Alberto and Beryl flared off the Southeast coast in May 2012.

MORE: NASA Images of Hurricanes