The other bad aspect the NHC is beating the drum about is Maria's forward motion. This cyclone isn't exactly setting any forward speed records. Considering the weaker ridge a long duration vortex interaction with the island, it will take a while for the eyewall to traverse the Puerto Rican landmass. The combination of high terrain and 15-20 inches of rain in places in a rapid fashion is incredibly troubling. People there need to get away from ravines, creeks, streams, etc., most likley all these features are going to turn into raging torrents and rivers. Also get off of steep ridges as mudslides and mudflows will be an absolute certainty with this type of event. A high population is a risk.