JACKSONVILLE, Fla. – A flurry of devastating storms the past two months has finally ended with a day pause and now Invest 90L has become Tropical Depression 16. An active gyre over Central America spawned the depression located close to Nicaragua.
The gyre cultivates a favored zone for development. TD 16 is embedded in the larger counter-clockwise flow around the Gyre which will track the depression around eastern gyre flank and into the Gulf. The Gyre will begin to decay Friday and Saturday but this will have no impact on weakening the depression.
The recent streak of named tropical systems lasted 37.75 days. The only other years with longer spans were 41.75 days in 1898 and 38.5 during the 2004 season when a record total of 8 named storms developed in August.
October arrived without a hurricane or tropical storm anywhere in the world but just 3 days later Tropical Depression 16 formed This month typically sees a greater number of systems developing in the Gulf and western Caribbean.
Hurricanes like Irma and Maria that track in from Africa decrease in frequency as dry air and shear pose challenges for storms in the eastern Atlantic.
Closer to Florida the threat jumps especially along the Gulf coast in October and this is the time to watch for a storm producing set up called the Central American Gyre.
When excessive tropical moisture combines with a large counterclockwise circulation 600-1200 miles wide over Central America thunderstorms fire up. If the conditions persist for more than 48 hours the gyre will produce tropical cyclones on the eastern side about 50% of the time according to grad researcher Philippe Papin at the University of Albany.
These gyres most often form 1.5 to 2 tropical storms a year typically in the late spring and early fall. They are most common in September, but can help generate systems into November.
Not every gyre set up produces a named storm but they all produce heavy rainfall.