NewsOctober 29, 2012

Hurricane Sandy Roars Ashore, Threatening Record Surge

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Andrew Freedman

By Andrew Freedman

After days of intense preparations, East Coast residents were beginning to feel the full effects of Hurricane Sandy on Monday as it brought tropical storm force winds to New York City, along with a damaging storm surge. Officials and homeowners from Delaware to Massachusetts were anxiously awaiting Monday evening’s high tide, which will occur just as the fiercest winds and waves pound the coastline, possibly causing a record storm surge in New York City, Atlantic City, and other vulnerable coastal locations.

Surf pouring over a sea wall in Ocean City, Md. as Hurricane Sandy approached the area.
Credit: Christopher Bressi/Facebook.

The storm will be felt as far inland as West Virginia and Tennessee, where blizzard warnings are in effect for higher elevations, as cold air wraps around the storm and dumps up to 3 feet of snow in some spots. By midweek, the storm could create record waves on the Great Lakes, as the storm spins its way west, and then northward into Canada.

Sandy has made an earlier turn toward the northwest than expected, which puts the central New Jersey coastline in the crosshairs for a potentially record high storm surge on Monday night. Already, the Monday morning high tide resulted in moderate-to-major coastal flooding in New Jersey and low-lying areas in New York City. Winds were gusting to 50 mph in New York before noon, and were expected to increase to 70- to 80-mph gusts by Monday night. Strong winds are forecast to spread inland and cover a massive area from Virginia to Massachusetts, eventually moving west to the Great Lakes. Even parts of Ontario, Canada will be impacted by this unusual storm.

The National Weather Service is warning of a “life threatening” storm surge threat all the way into southern New England, with 6- to 11-foot storm surge possible at The Battery in Manhattan, and in coastal Connecticut along Long Island Sound.

Computer models agreed that The Battery in Lower Manhattan, Sandy Hook, N.J., and Atlantic City will see the highest storm tides on record. That data goes back to 1893, 1932, and 1911, respectively. At The Battery, the prior record occurred during Hurricane Donna in 1960. As of noon ET, the central estimate for The Battery was slightly more than 6 feet above the Mean High Water level (mean high tide), which would top the storm tide (tide level along with the storm surge) from Hurricane Irene by more than a foot. For Sandy Hook, Hurricane Sandy could top Irene's storm tide by 1-to-2 feet.

In Bridgeport, Conn., the central estimate for surge was about 7.5 feet, which corresponds to a storm tide more than 5 feet above mean high tide. In Philadelphia, the surge may peak at one foot, but the tide could reach more than 2 feet above average. In Atlantic City, the central estimate for surge is about 5.5 feet, reaching about 5 feet above mean high tide. To figure out the particular risks for your local area, visit Climate Central’s interactive map

A record storm surge in New York City could flood the city’s subway system, which is the lifeblood of transportation in the region, since tunnel entrances are extraordinarily vulnerable to coastal flooding. In anticipation of the flood threat, city officials shut down the entire transit system as of 7 p.m. on Sunday, which was only the second shutdown in history. The first shutdown occurred just 14 months ago, when Hurricane Irene lashed the city with a 4.13 foot storm surge. That resulted in a total water level (how high the water got when looking at both the tide and storm surge) peaking at 4.8 feet above average high tide. As of Monday morning, a National Weather Service computer model and a model run by the Stevens Institute of Technology was projecting a peak storm tide — the water level reached when combining storm surge plus the tide — of at least 6 feet above average high tide close to the Monday evening high tide, which occurs at 8:13 pm at The Battery.

Satellite image of Hurricane Sandy as it rounded Cape Hatteras, N.C. on October 28.
Click to enlarge the image. Credit: NASA.

According to Climate Central’s Surging Seas mapping tool, there are approximately 308,000 New York City residents who live below 6 feet above the mean high water level, and storm surge models show the water rising to at least such a level during Monday night's high tide.

The storm is such a formidable coastal flood threat because of its massive wind field, with tropical storm force winds extending more than 500 miles from its center, setting a record for the largest hurricane observed in the North Atlantic. The wind field means that even though the storm will be coming ashore in New Jersey, damaging winds and power outages will be possible across the entire eastern third of the country, down to the Georgia/Florida border.

Washington, D.C., and Philadelphia are both in line to see wind gusts to at least 70 mph by Monday night, along with heavy rainfall, prompting the federal government to shut down for the day.

In the higher elevations of seven states from Maryland to Tennessee — including two key politically important swing states in next week’s presidential election, Ohio and Virginia — snow is the greatest threat from Hurricane Sandy. Accumulations of up to 3 feet or more are forecast in some spots, which could cause power outages and structural problems due to the heavy weight of the snow.

The storm is not only unusually large, it is also extremely powerful, thanks to abundant energy from the ocean, as water temperatures off the East Coast are running several degrees above average for this time of year, and energy from jet stream winds moving in from the southwest. The storm is already more powerful than the “Perfect Storm” in 1991, and has tied the record for the lowest air pressure reading ever recorded north of Cape Hatteras, N.C., which was set on Long Island during a 1938 hurricane.

Timing will be key to determining the storm surge and extent of the associated damage, since if the peak onshore winds occur around the time of high tide, that will maximize the surge. As of Monday morning, most computer models indicated that this worst-case scenario is likely — although not certain — to occur.

“A long duration coastal flood event is expected and moderate to major flooding this morning into early afternoon . . . and potential historic flooding tonight into early Tuesday morning,” the National Weather Service said in a statement. “The potential is high for significant inundation and damage to structures in historically flood prone spots.” Destructive waves of up to 12 feet in New York Harbor, and significantly larger in locations more exposed to the open ocean, could cause “significant damage to coastal structures.”

In addition to coastal flooding, high surf, with waves offshore measuring at least 30 feet in height, will help cause significant beach erosion.

Graphic showing the wide swath of tropical storm force winds (orange) and hurricane force winds (red) extending out from Hurricane Sandy.
Click to enlarge the image. Credit: National Hurricane Center.

During Monday morning’s high tide, significant coastal flooding was reported in some areas of Brooklyn, Atlantic City, parts of Connecticut, and Long Island.

The Weather Service has issued increasingly dire warnings for the coastal flooding risk, at one point on Sunday the office in Philadelphia put out this message to people who might have been reluctant to heed evacuation orders:


Climate Change Connection?

The storm track is being influenced by an unusually strong “blocking” pattern in the upper atmosphere, with a massive dome of high pressure located southwest of Greenland. Without this blocking, the storm would have been able to turn out to sea, without harming the U.S. It's an example of what can happen when blocking patterns appear at precisely the wrong time.

Additionally, there are many other ingredients that are converging to create this perfect storm, including a deep dip in the jet stream across the eastern U.S. that is playing a role in essentially capturing the storm and flinging it inland.

“History is being written as an extreme weather event continues to unfold, one which will occupy a place in the annals of weather history as one of the most extraordinary to have affected the United States,” wrote Weather Channel senior meteorologist Stu Ostro.

“A meteorologically mind-boggling combination of ingredients is coming together: one of the largest expanses of tropical storm (gale) force winds on record with a tropical or subtropical cyclone in the Atlantic or for that matter anywhere else in the world; a track of the center making a sharp left turn in direction of movement toward New Jersey in a way that is unprecedented in the historical database; a 'warm-core' tropical cyclone embedded within a larger, nor'easter-like circulation; and eventually tropical moisture and arctic air combining to produce heavy snow in interior high elevations,” Ostro said.

Recent studies, including Ostro's own work, have shown that blocking patterns such as the one that is currently over the Atlantic have appeared with greater frequency and intensity in recent years. Some scientists think that may be related to the loss of Arctic sea ice, which is one of the most visible consequences of manmade global warming. The 2012 sea ice melt season, which ended just one month ago, was extreme, with sea ice extent, volume, and other measures all hitting record lows. The loss of sea ice opens large expanses of open water, which then absorbs more of the incoming solar radiation and adds heat and moisture to the atmosphere, thereby helping to alter weather patterns. Exactly how weather patterns are changing as a result, however, is a subject of active research.

Global warming is also expected to alter hurricane frequency and strength, making North Atlantic hurricanes slightly more powerful, while reducing the overall number of storms during the coming decades. Detecting such changes in the observational record is difficult, considering the varying ways people have kept tabs on hurricanes prior to the era of hurricane hunter aircraft flights. A recent study published in the Proceedings of the National Academy of Sciencesfound that warmer sea surface temperatures are tied to an increase in stronger Atlantic hurricanes.

Regardless of any changes in hurricane intensity, storms are already likely to produce more signiifcant coastal flooding, since sea levels have been rising during the past century, due to a combination of warming ocean waters and melting of polar ice caps. If Hurricane Sandy were to strike New York City in 2050, it would cause even more damage, since sea levels are expected to be considerably higher by midcentury. A recent study found that sea level rise has taken place at an accelerated rate at locations north of Norfolk, Va., and if this pace continues the Northeast could see much higher sea levels than other parts of the East Coast by midcentury.

Related Content
Hurricane Sandy Set to Deliver Massive Blow to East Coast
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How Fujiwara Effect Will Toss Sandy Into U.S.
Officials Warn of Hurricane Sandy's Rare Damage Potential
How Hurricane Sandy Can Become a 'Frankenstorm'
Sea Level Rising Faster Than Average in Northeast U.S.

Helpful links for following the storm:
National Weather Service Storm Central
Climate Central Surging Seas Mapping Tool
New York Times Live Blog
Capital Weather Gang blog

Twitter Accounts to Follow: