south atlantic Subtropical cyclone Bapo: an unusual South Atlantic system

[Vorticity0123]

A very rare occurrence in the South Atlantic: a subtropical cyclone has developed to the southwest of Sao Paulo, being named Bapo by the Naval Hydrography Center of Brazil. This is the first officially named system since Arani in 2011. The synoptic chart from this agency shows the approximate location of the system:

 

Synoptic analysis for Brazil from the Naval Hydrography Center of Brazil. The center of Bapo is analysed as the "B" visible on the chart.

 

Upon checking the structure of Bapo via the GFS model, it seems that Bapo just meets the criteria of a subtropical cyclone, by having a warm core. On the other hand, the warm core is asymmetric, showing that the system is not fully tropical. See the chart below:

 

 

GFS phase analysis of Bapo.

 

The current 'position' of the cyclone is denoted by the C. The A indicates the starting position of the system, while the Z stands for the final position of the system as forecasted by the GFS. Taking a look at this shows that the C is located in the 'asymmetric warm core' part of the spectrum.

 

Alongside with this analysis, a forecast track is visible in the upper right corner of the system. Note that the current position already brings the system over sub-26*C sea surface temperatures, meaning the system will not live long, as weakening and extratropical transition seem to be on the way. This can also be seen on the phase diagram itself, as the system moves into 'cold core' territory. This is a characteristic of an extratropical, frontal system.

 

Sources:

http://www.mar.mil.br/dhn/chm/meteo/prev/cartas/C15020612.jpg

http://moe.met.fsu.edu/cyclonephase/gfs/fcst/archive/15020612/23.phase1.png

http://en.wikipedia.org/wiki/South_Atlantic_tropical_cyclone

[Somerset Squall]

Thanks for this Vorticity, I would've missed this one otherwise . An interesting system, it seems these systems are becoming more recognised now, with several systems being noted over the last couple years. But yes, this is the first named one since Arani.

http://en.m.wikipedia.org/wiki/South_Atlantic_tropical_cyclone

[Su Campu]

You mean south Atlantic.

[Gray-Wolf]

Are we seeing changes in this area of the Atlantic or did we just not spot these events before? I recall the 2011 event being heralded as a possible "shape of things to come" as the worlds oceans warm?

[summer blizzard]

Interesting.