New York City Peak Threat Hours: 7-10 PM When The Flooding Begins
As meteorologists have been repeating all day, the biggest threat for NYC is not so much the rain, or even the wind, dangling cranes hundreds of feet above ground notwithstanding, but the storm surge. The threat here is that Hurricane Sandy will hit land just as the tide comes in, resulting in a double whammy which Wunderground has called a "gigantic bulge of water that will raise waters levels to the highest storm tides ever seen in over a century of record keeping." Add to this the impact of the full moon, which means that high tide will be 5% higher than average for the month, and Wunderground's conclusion is inevitable: "This is a higher destructive potential than any hurricane observed since 1969, including Category 5 storms like Katrina, Rita, Wilma, Camille, and Andrew." How high are we talking: Sandy's storm surge will be capable of overtopping the flood walls in Manhattan, which are only five feet above mean sea level... According to the latest storm surge forecast for NYC from NHC, Sandy's storm surge is expected to be 10 - 12' above MLLW. Since a storm tide of 10.5' is needed to flood the subway system, it appears likely that portions of the NYC subway system will flood." Luckily for all, the NY Fed's tungsten gold, which is 50 feet below sea level (and 80 feet below the surface) and is in the Zone C flood evacuation area, will be perfectly "safe." And after all tungsten gold will never just float away.
Sandy already producing a record storm surge
The National Weather Service in Atlantic City, NJ said that isolated record storm surge flooding already occurred along portions of the New Jersey coast with this morning's 7:30 am EDT high tide cycle. As the tide goes out late this morning and this afternoon, water levels will fall, since the difference in water levels between low tide and high tide is about 5'. However, this evening, as the core of Sandy moves ashore, the storm will carry with it a gigantic bulge of water that will raise waters levels to the highest storm tides ever seen in over a century of record keeping, along much of the coastline of New Jersey and New York. The peak danger will be between 7 pm - 10 pm, when storm surge rides in on top of the high tide. The full moon is today, which means astronomical high tide will be about 5% higher than the average high tide for the month, adding another 2 - 3" to water levels. This morning's 9:30 am EDT H*Wind analysis from NOAA's Hurricane Research Division put the destructive potential of Sandy's winds at a modest 2.9 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'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 10 - 12' above MLLW. Since a storm tide of 10.5' is needed to flood the subway system, it appears likely that portions of the NYC subway system will flood. The record highest storm tide at The Battery was 10.5', set on September 15, 1960, during Hurricane Donna.
Observed storm tide (red line) and predicted storm surge for Hurricane Sandy at The Battery on the south shore of Manhattan, New York City, from the experimental Extratropical Storm Surge model, run by NOAA"s Meteorological Development Laboratory (green line) and the NYHOPS model from the Stevens Institute of Technology (pink curve), which uses a highly detailed 3D ocean model and even includes rainfall and tributary inflows. These models have a storm surge of 5 - 6', which brings the maximum storm tide--the water level reached as a result of the combined action of the tide and the storm surge--to 11' above MLLW (Mean Lower Low Water.) Irene brought a storm tide of 9.5' above MLLW to The Battery in 2011. At a storm tide of 10.5', water will likely pour into the Lower Manhattan subway system, unless efforts to sandbag the entrances are successful. The NWS in NYC is predicting a 10 - 12' storm tide at The Battery during tonight's 9 pm high tide cycle.
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And with 4 hours until the peak surge, NYC's Battery is already underwater.
Photo courtesy of @The_Domino