The disturbance I mentioned yesterday southeast of the Cape Verdes was upgraded to TD2 early Thursday morning based on visible, infrared, and microwave satellite imagery/data. Then six hours later, it was upgraded to Tropical Storm Bertha based again on improved satellite presentation. At 15Z (11am EDT), TS Bertha was located at 13.3N 24.7W and moving WNW at 12kts. Intensity is estimated at 35kts and 1006mb.
This was extraordinarily well forecast; models had predicted this formation last week. One week ago, Bertha was a large convective complex over Chad and Sudan in central Africa. Even since yesterday at this time, it has gotten much better organized in terms of surface circulation and concentration of the deepest convection over the center. Cloud-top temperatures are persistently colder than -70C now.
The SSTs are a little on the cool side, around 26C, but sufficient for genesis and moderate strengthening. Vertical wind shear (defined as the vector difference between the low-level 850mb winds and the upper-level 200mb winds) is very low over the system, and should remain that way for at least the next few days. Overall, environmental conditions favor intensification and a gradual movement to the WNW.
Please visit my tropical Atlantic headquarters.
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