The drawn-out demise of Chris

Chris is still barely hanging on as a tropical depression: a state he's now likely to remain in for the rest of the time he's around. What's keeping Chris from intensifying according to the NHC is "upper level convergence". Essentially convergence is when a bunch of air from different places is all trying to wind up in the same place. Divergence is the opposite. Tropical cyclones like upper level divergence, because this draws air upwards into the place vacated by the diverging air. Drawing warmer air from near the ocean upwards produces convection, and thus thunderstorms, which give the energy that the storm needs to intensify. In the image at the top of this page you can get a picture of how the rising convection goes along with the air spreading out (or diverging) at the top of the storm. When the air is instead converging at the top, it effectively keeps a lid on the convection, and less energy is released into the storm.