Aug 3, 2016

Earl rather low central pressure but still not a hurricane

Usually when tropical systems in the Atlantic basin have a central pressure around  992 millibars (29.29" Hg) the maximum wind speed is at least minimal hurricane force. Earl's latest central pressure has been just below 992 mbs for the past 12-15 hours and the wind still remain in the 65-70 mph range.

Earl is still expected to become a minimal (Category 1) hurricane today. However, it is interesting to note that it has yet to become one.Two possible reasons why it has not done so (and MAY NOT do so) are: 1) It now has the Isthmus of Central America to its south. This could be disrupting inflow into the lower level of the storm along with "relatively" drier air being drawn into the storm's circulation from off the isthmus (as depicted in image below).



2) Dropsonde data (plot of temperature and dew point from a specified height above ground downward to the surface) from recon aircraft indicates dry air between about the 900 millibar surface up to approximately 760 millibars (purple circle on image below).

Dropsonde plot courtesy of: http://aircraft.myfoxhurricane.com/

On the favorable side for intensification are very warm SST (Sea Surface Temperatures) and little shear along with a small area of high pressure aloft over the cyclone providing some favorable outflow.