This afternoon’s 3:30 pm EDT H*Wind analysis from NOAA’s Hurricane Research Division put the destructive potential of Sandy’s winds at a modest 2.8 on a scale of 0 to 6. However, the destructive potential of the storm surge was record high: 5.8 on a scale of 0 to 6. This is a higher destructive potential than any hurricane observed since 1969, including Category 5 storms like Katrina, Rita, Wilma, Camille, and Andrew. The previous highest destructive potential for storm surge was 5.6 on a scale of 0 to 6, set during Hurricane Isabel of 2003. Sandy is now forecast to bring a near-record storm surge of 6 – 11 feet to Northern New Jersey and Long Island Sound, including the New York City Harbor. This storm surge has the potential to cause many billions of dollars in damage if it hits near high tide at 9 pm EDT on Monday. The full moon is on Monday, which means astronomical high tide will be about 5% higher than the average high tide for the month. This will add another 2 – 3″ to water levels. Fortunately, Sandy is now predicted to make a fairly rapid approach to the coast, meaning that the peak storm surge will not affect the coast for multiple high tide cycles. Sandy’s storm surge will be capable of overtopping the flood walls in Manhattan, which are only five feet above mean sea level. On August 28, 2011, Tropical Storm Irene brought a storm surge of 4.13′ and a storm tide of 9.5′ above MLLW to Battery Park on the south side of Manhattan. The waters poured over the flood walls into Lower Manhattan, but came 8 – 12″ shy of being able to flood the New York City subway system. According to the latest storm surge forecast for NYC from NHC, Sandy’s storm surge is expected to be at least a foot higher than Irene’s. If the peak surge arrives near Monday evening’s high tide at 9 pm EDT, a portion of New York City’s subway system could flood, resulting in billions of dollars in damage. I give a 50% chance that Sandy’s storm surge will end up flooding a portion of the New York City subway system.
Animation compiled from NASA satellite images shows evolution and movement of the massive Hurricane Sandy: