In its final report on the how national forecasters handled Sandy (PDF), the National Oceanic and Atmospheric Administration concluded the public did not understand what a storm surge was or how dangerous it would be.
Yet it turned out that the surge, which reached nearly 14 feet at Manhattan's Battery, was far more deadly than the storm's tropical storm-force winds. More than half of the 43 people who died in the city during the storm drowned.
The report says the New York City Office of Emergency Management was confused about the storm surge forecast, and that it was only after a phone call from the National Hurricane Center 48 hours before the surge crested, that city officials understood how high the water would rise. Mayor Bloomberg's evacuation order followed about 12 hours later. The report says the communication breakdown "may have delayed critical decision-making about evacuations."
UPDATE: The Office of Emergency Management said in a statement the National Weather Service "surge forecast provided to OEM changed significantly between Oct. 27 and Oct. 28, from 4-8 feet to 6-11 feet. This was the key driver of the city's decision to order an evacuation on Oct. 28."