Hurricane Irene is now menacing the coasts of North and South Carolina, with winds of roughly 161 kilometers-per-hour kicking up waves as high as 5.5 meters tall. The Category 2 storm will continue northward in coming days but has already begun to weaken. That still gives it plenty of strength to blow over trees when it is forecast to come ashore again in the Northeast this weekend.

But, given that much of the U.S. East Coast will be on Irene's weak side, wind-wise, the biggest danger from this storm could be a storm surge high enough to swamp, say, New York City's subway system.

Plus, much of the region has already experienced near record levels of rainfall this August so the 900-kilometer-wide Irene is likely to touch off flash flooding with her predicted 20 centimeters or more of additional rain. As shown here, Irene will bring that much rain or more in places across the entire East Coast in the next five days, according to this forecast from the U.S. National Oceanic and Atmospheric Administration. And then there's always the possibility that tropical cyclone Irene could touch off the more pedestrian—but still destructive—land-based cyclones.