For the second time in 14 months, Greater New York is looking at a head-on strike by serious tropical weather. But Sandy and Irene don't appear to be similar storms. The incoming storm is much bigger, stronger and potentially more troubling for coastal communities, including New York City.

Hurricane Sandy prompted a series of mandatory evacuation orders along the eastern seaboard Saturday, including New Jersey's barrier islands, casinos in Atlantic City and New York's Fire Island. The most severe impact of the storm is expected to occur on Monday evening.

In New York City, officials on Saturday night decided not to order partial evacuations of low-lying neighborhoods, declining to adopt a precautionary measure used ahead of Irene's arrival in August 2011. Mayor Michael Bloomberg said he expected "a slow pileup of water, rather than a sudden surge" feared in the hours before Irene. He warned that Sandy might force a preemptive power shutdowns in Lower Manhattan and a possible closure of the transit system.

But even if Sandy has so far forced fewer evacuations in the city, there are reasons to suspect that the new storm is actually a more severe risk than Irene. Below, a guide to understanding the similarities and differences between the two big storms.

Strength: Irene was a weakening storm at landfall -- and Sandy is expected to reach land with more strength. In fact, the storm could still be growing when it reaches the region.