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Sunday, October 28, 2012

Jeff Masters: Sandy likely to be a multi-billion dollar disaster for the U.S.

by Dr. Jeff Masters5:28 p.m. GMT on October 27, 2012
Hurricane Sandy is holding its own against high wind shear of 30-40 knots, and has regained its Category 1 strength after falling to tropical storm strength early this morning. Sandy is a massive storm, with tropical storm-force winds that span a 660-mile diameter area of ocean from a point even with central Florida northwards to a point off the central North Carolina coast. Twelve-foot high seas cover a diameter of ocean 1,000 miles across. A buoy 150 miles east of Cape Canaveral, Florida, reported sustained winds of 63 mph, gusting to 76 mph, at 9:43 a.m. EDT. Another buoy about 100 miles east of the coast of Georgia reported sustained winds of 69 mph at 11:52 a.m. EDT. Due to the high wind shear and interaction with a trough of low pressure to Sandy's west, the storm has a rather unusual structure, with the strongest winds on the southwest side of the center, but a larger area of tropical storm-force winds to the northeast of the center. Satellite loops show that the low-level center of Sandy is partially exposed to view, with a small clump of heavy thunderstorms near the center. Most of the storm'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.

Figure 1. Early afternoon satellite image of Sandy.

Sandy's death toll at 48
Sandy was a brutal storm for the Caribbean, with a total death toll that now stands at 48. The death toll is highest in Haiti, with 34 dead. The toll will likely rise as remote areas cut off from communications are reached. Cuban state media is reporting that 11 people were killed on Cuba, and damage was heavy, with 35,000 homes damaged or destroyed. Cuba is probably the most hurricane-prepared nation in the world, and it is unusual for them to experience such a high death toll in a hurricane. Sandy was Cuba's deadliest hurricane since Category 4 Hurricane Dennis killed 16 people in 2005. Sandy is also being blamed for 1 death in Jamaica, 1 in the Bahamas, and 1 in Puerto Rico.

Forecast for Sandy
Wind shear is expected to remain a high 30-40 knots for the next two days, as Sandy interacts with a trough of low pressure to its west. The high shear should keep Sandy from intensifying the way most hurricanes do -- by pulling heat energy out of the ocean. However, a trough of low pressure approaching from the west will inject "baroclinic" energy -- the energy one can derive from the atmosphere when warm and cold air masses lie in close proximity to each other. Sandy's drop in central pressure from 969 mb at 5 a.m. to 960 mb at 8 a.m. this morning may be due, in part, to some baroclinic energy helping intensify the storm. This sort of effect helps spread out the storm's strong winds over a wider area of ocean; Sandy's diameter of tropical storm-force winds are predicted to expand from 660 miles to 760 miles by Sunday afternoon. This will increase the total amount of wind energy of the storm, keeping the storm surge threat very high. This morning's 9:30 a.m. EDT H*Wind analysis from NOAA's Hurricane Research Division put the destructive potential of Sandy's winds at a modest 2.3 on a scale of 0 to 6, However, the destructive potential of the storm surge was exceptionally high: 5.2 on a scale of 0 to 6. Sandy's large wind field will drive a damaging storm surge of 3-6 feet to the right of where the center makes landfall. These storm surge heights will be among the highest ever recorded along the affected coasts, and will have the potential to cause billions of dollars in damage. The latest set of 00Z (8 p.m. EDT) and 06Z (2 a.m. EDT) computer model runs have come into better agreement on the timing and landfall location of Sandy. Our two top models, the ECMWF and GFS, both call for landfall between 10 pm Monday night and 4 am Tuesday morning, with the center coming ashore between Delaware and New York City. 
A multi-billion dollar disaster likely in the U.S.
I expect Sandy's impacts along the mid-Atlantic coast and New England coasts to cost at least $2 billion in insured damage and lost business, and there is a danger the storm could cost much more. Steve Bowen, meteorologist for insurance broker AON Benfield, put it this way for me this morning: "Given the level of losses associated with Irene last year and the current projections of extended high wind, heavy rainfall, coastal surge and an inland flooding threat for many of the same areas with Sandy, it would not come as a complete surprise to see a multi-billion dollar economic loss." Sandy should bring sustained winds of 50-70 mph with gusts over hurricane force to a large 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 a billion dollars in wind damage.

Figure 3. 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. This model used winds from this morning's 12Z (8 a.m. EDT) run of the GFS model, and predicts that the peak storm surge from Sandy will reach 5.5' on Monday night October 29, which is 1.4' higher than Irene's storm surge. This forecast has the peak surge occurring near high tide, bringing the maximum storm tide -- the water level reached as a result of the combined action of the tide and the storm surge -- to 10.5', a foot higher than Irene. At this level, water will very likely pour into the Lower Manhattan subway system, unless efforts to sandbag the entrances are successful. Notice: this is not an official NHC storm surge forecast, and the storm surge may be higher or lower than this, depending upon the strength, track, and timing of Sandy.

Sandy's storm surge may flood New York City's subway system, costing billions
Sandy is expected to have tropical storm-force winds that extend out more than 400 miles from the center, which will drive a much larger storm surge than its peak winds would ordinarily suggest. The full moon is on Monday, which means astronomical tides will be about 5% higher than typical, increasing the potential for damaging storm surge flooding. Fortunately, Sandy is now predicted to make a fairly rapid approach to the coast, meaning that the storm surge will not affect the coast for multiple high tide cycles. If Sandy hits near New York City, as the GFS model predicts, the 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' 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. However, the town of Lindenhurst (population 28,000), on the south side of Long Island, was mostly under water due to the storm surge, and fresh water run-off from Irene's torrential rains, riding on top of a 3 to 4-foot storm surge, allowed the swollen East and Hudson Rivers to overflow at the edges of Manhattan. New York was not as lucky on December 12, 1992, when a 990-mb Nor'easter drove an 8-foot storm surge into Battery Park, flooding the NYC subway and the Port Authority Trans-Hudson Corporation (PATH) train systems in Hoboken, New Jersey. FDR Drive in lower Manhattan was flooded with 4 feet of water, which stranded more than 50 cars and required scuba divers to rescue some of the drivers. Mass transit between New Jersey and New York was down for ten days, and the storm did hundreds of millions in damage to the city. The highest water level recorded at the Battery in the past century came in September 1960 during Hurricane Donna, which brought a storm surge of 8.36 feet to the Battery and flooded lower Manhattan to West and Cortland Streets. According to the latest storm surge forecast for NYC from the experimental Extratropical Storm Surge model, run by NOAA"s Meteorological Development Laboratory, Sandy's storm surge may be higher than Irene's and has the potential to flood New York City's subway system (Figure 4.) The amount of water will depend critically upon whether or not the peak storm surge arrives at high tide or not. If the peak surge arrives near Monday evening's high tide near 9 p.m. EDT, a portion of New York City's subway system could flood, resulting in billions of dollars in damage. I give a 30% chance that Sandy's storm surge will end up flooding a portion of the New York City subway system.

An excellent September 2012 article in the New York Times (titled "New York Is Lagging as Seas and Risks Rise, Critics Warn") quoted Dr. Klaus H. Jacob, a research scientist at Columbia University’s Earth Institute, on how lucky New York City got with Hurricane Irene. If the storm surge from Irene had been just one foot higher,"...subway tunnels would have flooded, segments of the Franklin D. Roosevelt Drive and roads along the Hudson River would have turned into rivers, and sections of the commuter rail system would have been impassable or bereft of power," he said, and the subway tunnels under the Harlem and East Rivers would have been unusable for nearly a month, or longer, at an economic loss of about $55 billion. Dr. Jacob is an adviser to the city on climate change, and an author of the 2011 state study that laid out the flooding prospects. “We’ve been extremely lucky,” he said. “I’m disappointed that the political process hasn’t recognized that we’re playing Russian roulette.” A substantial portion of New York City's electrical system is underground in flood-prone areas. Consolidated Edison, the utility that supplies electricity to most of the city, estimates that adaptations like installing submersible switches and moving high-voltage transformers above ground level would cost at least $250 million. Lacking the means, it is making gradual adjustments, with about $24 million spent in flood zones since 2007. At a conference I attended this summer in Hoboken on natural hazards on urban coasts, I talked to an official with Consolidated Edison who was responsible for turning off Lower Manhattan's power if a storm surge floods the subway system. He said that he was ready to throw the switch during Irene, but was glad it turned out not to be needed. 
Sandy's rains
Sandy is expected to dump 5-10 inches of rain along the coast near the point the center comes ashore, and 3-4 inches several hundred miles inland. Higher isolated rainfall amounts of 15 inches are likely. Rains of this magnitude are going to cause trouble. If we compare the predicted rainfall amounts for Sandy (Figure 4) with those from Hurricane Irene of 2011 (Figure 5), Sandy's are expected to be about 20% 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 (Figure 6).

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 2-4 inches of rain (Figure 4), which is not enough to cause catastrophic flooding like occurred for Hurricane Irene. However, it is quite possible that the axis of heaviest rains will shift northwards from this forecast. I expect that river flooding from Sandy will cause less than $1 billion in damage.

To find out if you need to evacuate, please contact your local emergency management office. They will have the latest information. People living in New York City can find their evacuation zone here or use this map. FEMA has information on preparing for hurricanes.

People with disabilities and caregivers seeking information on accessible shelter and transportation can contact

Our Weather Historian, Christopher C. Burt, has an excellent post on Late Season Tropical Storms that have affected the U.S. north of Hatteras. He also has a post, Historic Hurricanes from New Jersey to New England.

Joe Romm at has a thoughtful piece called, How Does Global Warming Make Hurricanes Like Irene More Destructive?

For those of you wanting to know your odds of receiving hurricane force or tropical storm force winds, I recommend the NHC wind probability product.

Wunderground has detailed storm surge maps for the U.S. coast.

The National Hurricane Center's Interactive Storm Surge Risk Map, which allows one to pick a particular Category hurricane and zoom in, is a good source of storm surge risk information.

Research storm surge model run by SUNY Stonybrook for New York City.

Climate Central has a nice satellite image showing which parts of New York Harbor are below five feet in elevation.

Five-minute video of Hurricane Sandy on Thursday as seen from the International Space Station.

I'll probably leave this post up until late morning Sunday, unless there are some significant changes to report.

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