NewsFebruary 12, 2013

NWS Confirms Sandy Was Not a Hurricane At Landfall

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Andrew Freedman

By Andrew Freedman

In a technical report released on Tuesday, the National Oceanic and Atmospheric Administration (NOAA) reaffirmed its initial conclusion that Hurricane Sandy was no longer officially a hurricane when it made landfall on Oct. 29 near Brigantine, N.J., just north of Atlantic City. Instead, it was a “post-tropical cyclone” packing hurricane-force winds, the report said.

However, it also said that hurricane-force winds reached the New York coastline while the storm was still a hurricane, and that storm surge fatalities may have occurred while Sandy was officially a hurricane as well, raising additional questions about why no hurricane warnings were issued for any locations north of North Carolina.

Coastal flooding in Mantoloking, N.J., as taken from a New Jersey Air National Guard Helicopter.
Credit: NJNG/Scott Anema.

The tropical cyclone report brings an end to any debate within NOAA over whether or not the storm still had sufficient characteristics of a tropical weather system to hold on to the hurricane label at landfall. The classification of the storm carries significant implications for home and business owners, as well as insurers, since most hurricane insurance policies have deductibles that would have been triggered only if the storm still had been a named hurricane at the time of landfall, and if hurricane warnings were in effect. In this case, neither one of those conditions were met.

The storm is expected to be the second-most expensive storm on record in the U.S. since 1900, with damage in excess of $50 billion, behind only Hurricane Katrina.

The report provides the most in-depth summary of the storm’s evolution, structure, and impacts to date, and includes a comprehensive list of storm surge and inundation observations. It depicts a storm that had “quite unusual” hybrid characteristics that amplified its destructive power in the Mid-Atlantic and Northeast, particularly its large wind field, which powered a record storm surge that inundated large portions of the coastline from Delaware to Massachusetts.

Anticipating the storm’s transition into a post-tropical storm, the National Weather Service (NWS) never issued hurricane watches or warnings north of North Carolina, which has proven to be a controversial decision.

Critics, including some prominent television weathercasters, have questioned this decision by pointing out that more people might have heeded evacuation orders had hurricane warnings been put in place.

Hurricane Sandy approaches landfall in this enhanced satellite image from NOAA. 
Click to enlarge the image. Credit: NOAA.

The report provides some ammunition for those critics, particularly with its conclusion that it is possible that some storm surge-related deaths may have occurred before Sandy officially made its transition from a hurricane. “. . . it is nearly impossible to know exactly when these deaths occurred relative to the transition,” the report said.

Before Hurricane Sandy made its trek up the eastern seaboard, computer model projections showed that it would likely remain a hurricane for a time, but then transition to an extratropical storm system before making landfall. Since the Weather Service has different procedures and warning criteria for different types of weather systems, forecasters were faced with “unprecedented forecast and warning challenges,” the report said.

A purely tropical weather system mainly taps warm ocean waters for its strength, and has the strongest winds and rain closest to the center of the storm. An extratropical system, on the other hand, draws its power from large-scale temperature contrasts between warm and cold air masses, and has a far broader wind field and frontal features, such as cold and warm fronts.

Instead of risking a situation in which the Weather Service would have had to change its warnings at the last minute, the National Hurricane Center (NHC) directed local branch offices of the NWS to issue a hodgepodge of warnings, such as high-wind warnings, while refraining from issuing hurricane watches or warnings.

The extent of tropical storm force winds (orange) and hurricane-force winds (red) as Hurricane Sandy made its way along the East Coast on Oct. 28, 2012. 
Credit: NOAA/NHC.

The warnings that were issued may have affected the public’s decision-making process and public officials’ responses, including New York Mayor Michael Bloomberg’s initial press conference, when he told New Yorkers not to expect hurricane-like impacts from the storm. (Bloomberg later ordered widespread evacuations of low-lying parts of the city.)

“We would have liked to have been able to put up a hurricane warning,” said James Franklin, chief of forecast operations at the Hurricane Center in Miami, in an interview.

“[But] looking at it two to three days in advance we thought there were some really, really bad things that could have happened had we gone with the hurricane warning.” Dropping hurricane warnings during the middle of the event would have been interpreted as “the all-clear” by many people, Franklin said.

“We also knew in making decision that this was one of the most hyped up and publicized systems ever, probably, so we felt as though the message of a hazardous, life-threatening event was going to get out, and we made a lot of efforts to make sure that message would get out” regardless of the types of warnings that were issued, he said.

The NWS is considering two proposals that would give the Hurricane Center more flexibility to issue hurricane warnings if a similar situation arises.

Franklin said that the Weather Service uses a three-part definition to determine if a storm meets the necessary conditions for being classified as a tropical weather system or an extratropical one. In order to be a tropical system, such as a hurricane, Franklin said, it must have a warm core — meaning that the air near the storm’s center needs to be warmer than the air outside the core of the storm — it needs to have organized deep thunderstorms associated with it, and it needs to be free of warm and cold fronts, which are typical features of non-tropical weather systems. In Sandy’s case, shortly before the storm made landfall it did have a warm core, but it failed to meet the other two requirements.

“We’re very comfortable with saying it was not a tropical cyclone after 5 p.m. on the 29th,” Franklin said. “It simiply didn’t meet the definition.”

The report said that the storm caused 72 direct deaths in the U.S., which was the most from any U.S. cyclone since Tropical Storm Agnes in 1972. A majority of the deaths occurred as a result of storm surge flooding, including 21 surge-related deaths in low-lying sections of Staten Island alone, where an evacuation order had been issued by Bloomberg.

The report said that Staten Island and portions of Manhattan, along with hard-hit areas of the Jersey Shore, saw inundation levels of 4-to-9 feet above ground level. At the Battery in Lower Manhattan, the storm tide of 14.06 feet above Mean Lower Low Water, was 4.36 feet higher than the previous record. The report also found that flooding occurred 100 nautical miles north of New York City, in Columbia and Greene Counties, due to the storm surge up the Hudson River.

The storm damaged or destroyed 650,000 houses, and caused about 8.5 million customers to lose power. It caused “unprecedented” catastrophic damage to the New Jersey shore, and an estimated $19 billion in damage to New York City alone.

The tropical cyclone report is separate from an ongoing assessment of NOAA’s performance prior to, during, and after Hurricane Sandy.

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