I was having a hard time reconciling these images with those on the National Hurricane Center site, here: http://www.nhc.noaa.gov/psurgegraphics_at4.shtml?gm

Looking at the Weather Underground images, it took me a while to realize that they aren't predictions relative to Irene or any particular storm. They are Maximum of the "Maximum Envelope of Waters" plots, basically the worst case scenario for a storm in the middle of the category ranges depicted. Still good to plan for the worst, considering how hard it is to predict a given storm. The predictions from the NHC might be useful as best case scenarios.