14 September 2016

Julia forms over Florida, Ian still a tropical storm, TD12 forms over Cabo Verde Islands

The peak of hurricane season isn't failing this year.  There are two active tropical storms, and a new tropical depression off the coast of Africa.

The tenth named storm of the season, Julia, formed near Jacksonville FL on Tuesday night.  It actually formed over land, and the center has not spent any time over water, and probably never will.  This is extraordinary, and from what I can tell, unprecedented.  While there are a dozen examples of Atlantic tropical cyclones forming inland near a coastline (Agnes 1972 over the Yucatan Peninsula, Leslie 2000 over northern Florida are two examples), they did eventually track over water and strengthen. Julia can be traced back to an easterly wave that left the African coast on September 1st.

Tropical Storm Julia on Wednesday morning.  Previous center locations are marked with red dots.
Julia is expected to weaken to a depression later today over South Carolina... the primary threat is heavy rainfall, and parts of eastern SC could receive 6-10" of rain over the next few days as it crawls northward.

During an average season (using a 1981-2010 climatology), the 10th named storm forms on October 10th, so this season is now about 3.5 weeks ahead by that measure.  But in terms of ACE (Accumulated Cyclone Energy), the season is still at roughly 73% of average for this date.

In the far eastern Atlantic, over the Cabo Verde Islands, Tropical Depression 12 has formed and could get named in the next day or two.  The next name on the list is Karl, a name that was on one of the original six lists of names in 1980.

Models strongly favor this depression to develop to at least a tropical storm, and they also agree on a track toward the west over the next 5 days.  On this general trajectory, the system would reach the Lesser Antilles by late next week. But it will likely struggle with wind shear and dry air for the next three or so days.

A selection of global and regional dynamical model forecast tracks for TD12, valid out through Monday morning.
Finally, as expected, Tropical Storm Ian has not intensified, and is embedded in strong vertical wind shear in the middle of the Atlantic.  It is no threat to land, and is forecast to transition to an extratropical cyclone by the weekend.

Visible satellite image of Tropical Storm Ian on Wednesday morning.
Forecast track of Ian over the next five days. (NOAA/NHC)


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