Dr. Jeff Masters:
Irene is forecast to move to the northwest, passing over the northwest Bahamas by Thursday evening, then curving to the northeast. Irene then makes landfall in the US near or at the Outer Banks Saturday afternoon, then traveling along the mid-Atlantic coastline of the US. Sunday, Irene may make secondary landfall anywhere from New Jersey to Long Island and the southern New England coastline. In my opinion, New York City may be significantly impacted by Irene. It is also important to note that the windfield of Irene is expected to be large, affecting areas distant from the immediate track of Irene's center. Tropical storm forces winds are expected to be found out to at least 150 miles away from Irene's center on Friday afternoon.
NHC is forecasting for Irene to become a Category 4 storm (winds faster than 130 mph) by Thursday morning.
The storm surge (rise in water) could be 10-15 feet, Masters warns, which would put a good deal of lower Manhattan under the surface.