Yeah but what weather situation or combination makes them think that Irma will do that?
Irma has been steered to the West and then WNW by a high to the North. The high is forecast to ‘nose out’ around Florida - Irma will reach the periphery of that high pressure and the steering currents from a trough to the North will pull in that direction at that point. It all depends if the high noses further west or not.
Also the high to the north is being broken down by a cold front moving east from the mainland. Seems like where those two meet, cold front trough and Irma, will be the point she heads north. Simply because the high will obviously be gone at the point. In fact, irma could even turn to the NE. And might even turn as early as Nassau. At this point, that is our only hope.