Dangerous Hurricane Sandy continues north past North Carolina
By Dr. Jeff Masters
Published: 9:58 PM GMT on October 28, 2012
Hurricane Sandy has changed little in intensity today, and remains a very large, powerful hurricane. Sandy is going to cause billions of dollars in damage Monday and Tuesday in the Eastern U.S. due to storm surge, high winds, and heavy rains. Sandy is of near record-size, with tropical storm-force winds extending up to 520 miles from its center, covering an area larger than a Texas-and-a-half. This afternoon, Sandy brought winds gusting to 64 mph at Cape Hatteras, NC, 60 mph at Kitty Hawk, NC, and 60 mph at Cape Henry, VA. Sandy's rain is onshore from North Carolina to New Jersey and Pennsylvania. Jacksonville, NC and Suffolk, NC have recorded 2 inches of rain today, Greenville, NC has seen 1.6 inches, and Ahoskie, NC has seen 1.5 inches.
With peak impact still 24 to 36 hours away, water levels are already 2 - 4 feet above normal from Virginia to New York. At 4 pm EDT, Lewes, Delaware was at 3.3 feet above normal, Cape May, New Jersey was at 3.1 feet above normal, Wachapreague, Virginia was at 3.6 feet above normal, and Chesapeake Bay Bridge Tunnel station was at 3.6 feet above normal, up more than half a foot since 10:30am. The National Weather Service in Upton, New York mentioned today that the predicted maximum water level of 11.7 feet at The Battery in New York City, which is expected to occur at 8:13pm ET on Monday, would break the record of 10.5 feet which was set on September 15, 1960 in Hurricane Donna.
In a poignant, powerful Public Information Statement this afternoon, the National Weather Service in New Jersey is begging that people heed warnings, and evacuate if they are asked to. They write, "If you are reluctant [to evacuate], think about your loved ones, think about the emergency responders who will be unable to reach you when you make the panicked phone call to be rescued, think about the rescue/recovery teams who will rescue you if you are injured or recover your remains if you do not survive."
Intensity and Track Forecast for Sandy
Most of Sandy's heavy thunderstorm activity is on the storm's west side, in a thick band several hundred miles removed from the center, giving Sandy more the appearance of a subtropical storm rather than a hurricane. However, satellite loops show Sandy is steadily looking more tropical, with heavy thunderstorms increasing in areal extent near the center, due to a reduction in wind shear from 35 - 40 knots last night to 20 - 25 knots this afternoon. Wind shear is expected to remain near 20 knots until landfall, and Sandy will be traversing the warm waters of the Gulf Stream. These factors may allow Sandy to intensify by 5 - 10 mph over the next 24 hours. Sandy does not have time to build a complete eyewall and undergo rapid intensification. By Monday afternoon, Sandy will be moving over cool 25°C waters, which should slow down intensification by pulling heat energy our of the ocean. However, the trough of low pressure that will be sucking in Sandy to the northwest towards landfall will strengthen the storm by injecting "baroclinic" energy--the energy one can derive from the atmosphere when warm and cold air masses lie in close proximity to each other. Sandy should have sustained winds at hurricane force, 75 - 80 mph, at landfall. Sandy's central pressure is expected to drop from its current 953 mb to 945 - 950 mb at landfall Monday night. A pressure this low is extremely rare; according to wunderground weather historian Christopher C. Burt, the lowest pressure ever measured anywhere in the U.S. north of Cape Hatteras, NC, is 946 mb (27.94") measured at the Bellport Coast Guard Station on Long Island, NY on September 21, 1938 during the great "Long Island Express" hurricane. The latest set of 12Z (8 am EDT) computer model runs show a little faster motion for Sandy, bringing the center ashore in New Jersey Monday evening near 8 pm EDT.
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 use 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 9.7 - 10.8'. Irene brought a storm tide of 9.5' 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. Notice: these are not an official NHC storm surge forecast.
Sandy's storm surge a huge threat
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.
Sandy's winds
Sandy will bring sustained winds of tropical storm-force to a 1000-mile swath of coast on Monday and Tuesday. Winds of 55 - 75 mph with gusts over hurricane force will occur along a 500 mile-wide section of coast. With most of the trees still in leaf, there will be widespread power outages due to downed trees, and the potential for several billion dollars in wind damage. A power outage computer model run by Johns Hopkins University predicts that 10 million people will lose power from the storm.
Sandy's rains
Sandy's heavy rains are going to cause major but probably not catastrophic river flooding. If we compare the predicted rainfall amounts for Sandy with those from Hurricane Irene of 2011, Sandy's are expected to be about 30% less. Hurricane Irene caused $15.8 billion in damage, most of it from river flooding due to heavy rains. However, the region most heavily impacted by Irene's heavy rains had very wet soils and very high river levels before Irene arrived, due to heavy rains that occurred in the weeks before the hurricane hit. That is not the case for Sandy; soil moisture is near average over most of the mid-Atlantic, and is in the lowest 30th percentile in recorded history over much of Delaware and Southeastern Maryland. One region of possible concern is the Susquehanna River Valley in Eastern Pennsylvania, where soil moisture is in the 70th percentile, and river levels are in the 76th - 90th percentile. This area is currently expected to receive 3 - 6 inches of rain, which is probably not enough to cause catastrophic flooding like occurred for Hurricane Irene. I expect that river flooding from Sandy will cause less than $1 billion in damage.
There's a lot of good information out there. But the forecast isn't the same for everyone, and you have to interpret the data accurately.
