At first glance Tropical Storm Beta may be trying to form an eye. The latest microwave pass seems to show an eyewall trying to form. If this 'eyewall' were to solidify it would easily make way for rapid intensification.
The first question to ask yourself is whether that ring of active convection is surrounding the center of circulation. By overlaying the microwave image on top of the visible it seems to be fairly close. I will have more on this as I can find it.