23 July 2013

New disturbance exits Africa

An energetic African easterly wave made its way over the far eastern Atlantic this past Sunday, and is now centered just south of the Cape Verde Islands (about 12N 24W).  There is a 1008mb surface Low associated with the wave, as well as fairly persistent thunderstorm activity.


Presently, it's over marginally warm ocean temperatures (in the 26-27C ballpark), is experiencing very little vertical wind shear, and the mid-level atmosphere is relatively moist.  All of these factors combine to suggest that this could easily continue to develop and become a Tropical Depression or Tropical Storm in the near future.  If it becomes a tropical storm, the next name on the list is Dorian.  (Dorian is a new name in the ration this year... it replaces Dean from the 2007 season).

However, starting around Thursday, it should encounter much drier mid-level air, and somewhat cooler ocean temperatures.  I would bet that any strides it makes toward organization today and Wednesday will be halted or undone on Thursday and Friday.  It doesn't do much good to look beyond that period yet, since neither humans nor models have a reliable idea what condition the vortex will be in at that point.  The plot below shows model forecast tracks over the next five days, but keep in mind there is no official NHC forecast yet since it's not even a Depression.


This far out, the long-term track is immensely uncertain.  It's worth pointing out that on average, a storm in this location would take about 12-14 days to reach southern Florida (for example), or 5-6 days to even reach the Lesser Antilles.  So it's nothing to get concerned about now, but as always, warrants watching!

For disturbances this far away from the U.S., we rely on satellite data and any ships or buoys that might be in the vicinity -- traditional manned reconnaissance aircraft cannot reach these remote corners of the basin.  However, for a second year, NASA will be conducting a field program called HS3 (Hurricane Severe Storm Sentinel) in which two unmanned Global Hawk drones fly over tropical cyclones in the Atlantic to collect data on the storm structure and environment.  In tomorrow's update, I'll describe this program in more detail.

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