The information comes from the website of Triangle Tesla, which is a Tesla owners' organization independent from the carmaker. The site contains a wealth of emergency information for Tesla drivers in the affected region, including tips how to evacuate safely, and whether any North/South Carolina area Superchargers are congested or offline. Triangle Tesla also reminds owners to take their mobile charge connector with them when leaving towards a safer area, and that slowing down is the best way to extend range on the road.
A year ago when Hurricane Irma struck Florida, Tesla also remotely bumped some locked-capacity battery cars from 60 kWh to 75 kWh to give the cars an extra 30-40 miles of range in evacuation conditions. The over-the-air range improvement done now is similar.