Even though the “official” start of the 2015 Atlantic Hurricane Season is on June 1, there have been many cases of tropical storms and even hurricanes that have roamed the Atlantic waters prior to that date. While the majority of these have been weak and remained offshore, there are a few notable storms in our hurricane database. At least one tropical storm has been recorded in the Atlantic Ocean every month of the year with a hurricane being observed every month except February and April. There are many reasons why tropical cyclones tend to form almost exclusively in the Summer and Autumn. Some of these factors include favorable sea surface temperatures and the northerly progression of the Intertropical Convergence Zone (ITCZ). The ITCZ is responsible for producing many of the precursor disturbances that form into tropical storms and hurricanes but travels between the Tropic of Cancer and Tropic of Capricorn as the year progresses.
During the month of January we have seen one hurricane and one subtropical storm form. In addition, a tropical storm in 2005 and a hurricane in 1954 formed in December and lasted into the following January. One of the most unusual early season tropical cyclones was a recently discovered hurricane that developed from a non-tropical low pressure in the open Atlantic southwest of the Azores on January 1st, 1938. The storm tracked south and then southwest, an atypical storm motion in the open Atlantic, while acquiring tropical characteristics eventually becoming an 80 mph hurricane. The storm dissipated on January 6th well to the east of the Lesser Antilles with minimal impacts. Another quirky hurricane impacted parts of the Lesser Antilles in January 1955. It moved from the northeast to the southwest into the Caribbean Sea causing $600,000 in damage. Operationally, this hurricane was not recognized as a tropical cyclone until January 2nd so it was given the first name on the 1955 season list which was Alice. However, Alice actually became a tropical storm on December 30th, 1954 meaning it should have been given the next name on the 1954 list. As a result, the 1954 hurricane season officially has two storms that start with the letter A while 1955 does not have an A named storm.
February and March are far less interesting with only one tropical cyclone each. The February event formed on February 2nd, 1952 and impacted parts of Mexico, Cuba, and Florida with minimal impacts. It was a quick moving storm that quickly became extra-tropical after emerging into the Atlantic from Florida. This tropical storm was dubbed the “Groundhog Day” Storm. Moving on to March, the only tropical cyclone to exist occurred in 1908. Like Hurricane Alice, this unnamed hurricane developed northeast of the Lesser Antilles and moved towards the southwest. This hurricane had peak winds of 100mph, a Category 2 hurricane, and caused some damage to St. Bart’s though the monetary value is not known.
Tropical cyclone activity in April is also fairly rare with only one tropical storm and one subtropical storm in our database. The first storm formed in 1992 and was a short-lived subtropical cyclone that was located well to the northeast of Puerto Rico. The second and more interesting storm was Tropical Storm Ana in 2003. A non-tropical storm system formed on April 18th southwest of Bermuda. Convection began to develop around the system as it gradually acquired tropical characteristics. The storm became subtropical on April 20th while west of Bermuda and within 24 hours was considered a fully tropical system. Ana caused breezy weather and dropped over 2 inches of rainfall on Bermuda as it finally began to move off to the east. Bermuda would be the only country that would see direct impacts from Ana as a tropical cyclone but Ana would later bring breezy conditions to the Azores and rain to the United Kingdom as a post-tropical cyclone. Swells from Ana also impacted the United States and killed two when a boat capsized off of Jupiter Inlet, Florida.
The month of May has seen 24 tropical or subtropical cyclones develop since the official hurricane database began in 1851. While this number is much higher than any of the earlier months, it averages to one event every six or seven years. The last tropical cyclone to form in May was Tropical Storm Beryl in May 2012. As the name would imply, May 2012 also saw the formation of Tropical Storm Arthur about a week prior. While both storms impacted the United States, Arthur only caused minimal damage while Beryl produced $148,000 in damage and killed one person. Only three years featured two pre-season events, 1887, 1908, and 2012. The strongest pre-season hurricane was Hurricane Able which formed in May 1951. Able become a Category 3 hurricane with maximum sustained winds of 115mph. Despite its ferocity, Able stayed offshore and caused minimal damage to the United States. Prior to becoming a major hurricane off the North Carolina coast, Able did a counter-clockwise loop north of the Bahamas. A complete list of January-May subtropical storms, tropical storms, and hurricanes in included below.
| Name | Month | Year | Intensity | Max. Winds |
| Unnamed | May | 1863 | Cat. 2 Hurr. | 105mph |
| Unnamed | May | 1865 | Trop. Storm | 60mph |
| Unnamed | May | 1887 | Trop. Storm | 70mph |
| Unnamed | May | 1887 | Trop. Storm | 60mph |
| Unnamed | May | 1889 | Cat. 1 Hurr. | 80mph |
| Unnamed | May | 1890 | Trop. Storm | 60mph |
| Unnamed | March | 1908 | Cat. 2 Hurr. | 100mph |
| Unnamed | May | 1908 | Cat. 1 Hurr. | 75mph |
| Unnamed | May | 1916 | Trop. Storm | 60mph |
| Unnamed | May | 1932 | Trop. Storm | 50mph |
| Unnamed | May | 1933 | Trop. Storm | 45mph |
| Unnamed | May | 1935 | Trop. Storm | 60mph |
| Unnamed | January | 1938 | Cat. 1 Hurr. | 80mph |
| Unnamed | May | 1940 | Trop. Storm | 60mph |
| Unnamed | May | 1948 | Trop. Storm | 50mph |
| Able | May | 1951 | Cat. 3 Hurr. | 115mph |
| Unnamed | February | 1952 | Trop. Storm | 50mph |
| Alice | May | 1953 | Trop. Storm | 70mph |
| Alice-2 | Dec./Jan. | 1954/1955 | Cat. 1 Hurr. | 80mph |
| Arlene | May | 1959 | Trop. Storm | 60mph |
| Alma | May | 1970 | Cat. 1 Hurr. | 80mph |
| Alpha | May | 1972 | Subtrop. Storm | 70mph |
| Unnamed | May | 1976 | Trop. Storm | 50mph |
| Unnamed | January | 1978 | Subtrop. Storm | 45mph |
| Arlene | May | 1981 | Trop. Storm | 60mph |
| Unnamed | April | 1992 | Subtrop. Storm | 50mph |
| Ana | May | 2003 | Trop. Storm | 60mph |
| Zeta | Dec./Jan. | 2005/2006 | Trop. Storm | 65mph |
| Andrea | May | 2007 | Subtrop. Storm | 60mph |
| Arthur | May | 2008 | Trop. Storm | 45mph |
| Alberto | May | 2012 | Trop. Storm | 60mph |
| Beryl | May | 2012 | Trop. Storm | 70mph |
While tropical storms and hurricanes do not often form during the winter and spring months in the Atlantic, a total of thirty-two events have occurred since our official database started in 1851. While the majority of these stay away from land and are weak, their genesis and track are often unusual. Research has been done to correlate early season tropical cyclones with the total number of tropical cyclones but there is no significant connection. Some seasons can start early but still have below normal activity overall (1992 is a great example) while a season with a late start can produce an above normal amount of tropical cyclones. We haven’t seen a pre-season storm in the last two years and with six weeks to go before June 1st, it has yet to be seen if Tropical Storm Ana forms during in April or May.