NewsOctober 28, 2012

Hurricane Sandy Set To Deliver Massive Blow to East Coast

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Andrew Freedman

By Andrew Freedman

Hurricane Sandy is poised to deliver a potentially historic and devastating blow to the Mid-Atlantic and Northeast, with a record storm surge predicted for New York City and coastal Connecticut. Hurricane force wind gusts are expected to lash areas from near Washington D.C., all the way to Cape Cod, as a storm of unparalleled strength and size takes a track that is virtually unprecedented — almost due east to west — as it comes ashore in central to northern New Jersey. The storm, which is part hurricane, part nor'easter, is expected to eventually affect the entire eastern third of the country with everything from inland flooding to mountain snows.

The storm's effects may be felt all the way inland to the Great Lakes, and northward as far as Toronto. At least 10 million people may lose power, according to an analysis from Johns Hopkins University, as winds are projected to gust as high as 80 mph in the Philadelphia and New York City metropolitan areas, with damaging winds eventually spreading well inland. New York City has already taken steps to evacuate 375,000 residents.

Computer model projection for sea level pressure and winds a few thousand feet above the surface as Hurricane Sandy crosses the New Jersey coastline on Tuesday morning, from the GFS model.
Credit: Weatherbell Models.

Officials said the storm’s large size — it has already set a record for its expansive wind field, with tropical storm force winds extending more than 500 miles from the storm's center — makes it a fearsome coastal flood threat.

“Sandy is a large hurricane, and large systems pose multiple hazards for more people than smaller systems of comparable intensity,” said National Hurricane Center director Rick Knabb during a media briefing on Sunday.

Beginning Monday morning, high winds are expected to rake the Northeast corridor from Washington to Boston, with maximum gusts from Chincoteague, Va., to Chatham, Mass., reaching hurricane force (greater than 74 mph) on Monday night into Tuesday morning. That includes New York City, Long Island, Connecticut, and Rhode Island.

The strong winds, along with power outages, are forecast to spread well inland into Pennsylvania, upstate New York, and as far west as Ohio by midweek, as the storm slowly meanders over the eastern third of the country.

Evacuations ordered for New York City residents

As projected, the center of Sandy would be to the northeast of the Carolinas on Sunday, and then hook northwest and approach the coast in southern to central New Jersey late Monday or early Tuesday. Sandy's track has no historical comparison, and would be a worst-case scenario for New York City and Southern New England because of the tremendous east-to-southeasterly winds, which will drive water toward New York Harbor and coastal Connecticut, possibly breaking flood records that have stood since the 19th century.

The threat to New York City is particularly dire, since storm surge models are projecting that the surge will be considerably larger than during Hurricane Irene in 2011, when there was only minor coastal flooding. The city’s subway tunnels are extremely vulnerable to coastal flooding, and a disaster was averted by mere inches during Irene, making it more likely that flooding will occur in some sections of the system this time, particularly in parts of Brooklyn and Lower Manhattan. If the tunnels do flood, as suggested by the storm surge forecasts, it could cripple the lifeblood of transportation in and around the city for an extended period.

In light of the flood threat, New York City officials decided to shut down the entire mass transit system starting at 7 p.m. on Sunday. It's only the second time such a step has been taken, and the second year in a row it has been ordered. In addition, on Sunday morning New York City mayor Michael Bloomberg ordered the mandatory evacuation of about 375,000 people living in flood-prone areas of the city. Bloomberg had been criticized by meteorologists for not ordering the evacuation on Saturday, despite weather warnings.

Nighttime satellite image of Hurricane Sandy from NOAA/NASA's Suomi NPP satellite. City lights can also be seen in this image, outlining the state of Florida in the lower lefthand corner.Click to enlarge the image. Credit: U. Wisc./CIMSS.

During Hurricane Irene, the city recorded a 4.13 foot storm surge at The Battery in Lower Manhattan, and the total water level (how high the water got when looking at both the tide and storm surge) peaked at 9.5 feet. As of Sunday morning, a National Weather Service computer model was projecting a peak storm tide — the water level reached when combining storm surge plus the tide — of 11.7 feet, with a surge component of more than 5 feet (relative to Mean Lower Low Water Level (MLLW)). If that water level were to verify, it would break the record of 10.5 feet set on Sept. 15, 1960 during Hurricane Donna, the National Weather Service said. Other models put the projected storm surge closer to the level seen during Irene.

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 from the Stevens Institute of Technology show the water rising to at least such a level during Monday night's high tide.

In fact, the National Hurricane Center is predicting that water will reach between 6 and 11 feet above ground level if the peak surge occurs at the time of high tide. “GIVEN THE LARGE WIND FIELD ASSOCIATED WITH SANDY . . . ELEVATED WATER LEVELS COULD SPAN MULTIPLE TIDE CYCLES RESULTING IN REPEATED AND EXTENDED PERIODS OF COASTAL AND BAYSIDE FLOODING,” the Hurricane Center said.

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.

“A long duration coastal flood event is expected,” the National Weather Service said. “The potential is increasing for significant inundation and moderate damage to structures in historically flood-prone spots. Record coastal flooding may also occur in coastal Connecticut, as strong east-to-southeasterly winds drive the waters of Long Island Sound toward the coast.”

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 expansive tropical storm force wind field from Hurricane Sandy (orange area) and the hurricane force wind field (red area).
Credit: National Hurricane Center

Hurricane Sandy is noteworthy not just for its size, but also for its intensity. If the storm were to make landfall at its current intensity, it would set records for the lowest air-pressure readings ever recorded in New Jersey and coastal New York, beating benchmark storms such as the 1938 hurricane. However, many computer models project that the storm will intensify further prior to coming ashore.

In part, the storm is feeding off of much warmer-than-average ocean waters located off the East Coast. Sea surface temperatures hit record highs off the New Jersey and New England coasts this summer, and warmer water can help maintain a hurricane, or hurricane-like hybrid storm, much farther north than they would typically be able to survive at this time of year. Sandy is tapping into energy from both the ocean and the jet stream, as researcher Adam Sobel explained.

The multifaceted storm is expected to dump upwards of 5-to-10 inches of rain or more along its path, potentially leading to extensive inland flooding. On top of that, as cold air wraps into its circulation, rain may change to snow in the higher elevations of Maryland, West Virginia, Virginia, and Pennsylvania, potentially dumping upwards of 2-to-3 feet in some locations.

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 a menacing situation, 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 Sciences found 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.

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