I got an email today from Jim asking about 'Wind City Wendy' transitioning to a tropical system near Newfoundland. (He claims to own the naming rights.) How could I pass up the opportunity to talk about this?
I think what we are seeing there is a manifestation of autumn. The thing that really defines a warm core system is when the central core of the storm has a higher potential temperatue than the general circulation around it. (This is represented by the sign of the thermal wind value in the following model chart.) In this case what we are probably seeing is the uplift of moist oceanic air from an open North Atlantic. The air aloft there is probably going to be VERY cold when it reaches northern Canada. At that point the uplift of any oceanic air would result in a significant release of latent heat from condensation. Considering the frigid surroundings I could easily see this producing a warm-core system (which is what we are seeing in the models).