Invest 97L has now been upgraded to Sub Tropical Depression Seventeen as of the 5am advisory from the NHC. Although Sub Tropical Depression Seventeen is still classified as sub tropical, it is very close to becoming a tropical system. Again, the difference between a sub tropical versus a tropical system is that in a sub tropical system, the center if the system is cold core and the strongest winds are away from the center. In a tropical system, the center of the is warm core and the strongest winds are in the center. A warm core allow the venting of the storm to be pushed out at the top of the system.
There is an upper level low is within the area of where Sub TD Seventeen is but this is headed southeast and is forecast to weaken. This will allow Sub TD Seventeen to be in a more favorable area for strengthening. Along with warm waters and light shear, slow intensification is forecast and the transition from sub tropical to tropical is also forecast. Vertical shear is forecast in a few days so any strengthening will be halted at that time. The depression at the moment it headed NW and is being steered by the upper level low and a very large ridge in the Central Atlantic. The ridge is forecast to erode in a few days and a series of mid-latitude troughs that are near the SE US coast will force the depression on a NE track and away from any land masses.
The GFS model along with Euro model are now forecasting a developing system in the western Caribbean. Whether the other models begin see this system or not, and even if the GFS and Euro models are correct, that system will be picked up and head over Eastern Cuba and then out to sea.
