Tuesday, October 30, 2012

Nearest Precedent for Hurricane Sandy

I was a little surprised to see the Financial Times stating the following about Hurricane Sandy:
Although late-season hurricanes sometimes undergo a similar “extra-tropical transition” as they travel up from the tropics, this normally happens safely out to sea over the Atlantic. Sandy’s path is extremely unusual because a static area of high pressure south of Greenland has blocked the jet stream route northeastward across the ocean and instead forced the hurricane into the continental US.

“There is no precedent in hurricane records extending back to 1851 of a storm at this latitude taking this path,” said Mark Saunders, professor of climate prediction at University College London.
The track is certainly unusual but it's not unprecedented.  Most of the time hurricanes do veer off to the east at high latitudes - 2008 is pretty typical:

However, a search of the hurricane track archives at the National Hurricane Center turned up a precedent that turned in and attacked the north-east: hurricane Agnes in 1972:

Like Sandy, it was headed north east and then turned into the US Atlantic coast and made landfall near New York City as a strong tropical storm.  According to the Wikipedia, Agnes was at the time the costliest hurricane to hit the United States, and:
The most significant effects, by far, occurred in Pennsylvania, mostly due to severe flooding. In both Pennsylvania and New Jersey combined, about 43,594 structures were either destroyed or significantly damaged. In Canada, a mobile home was toppled, killing two people. Overall, Agnes caused 128 fatalities and nearly $3 billion (1972 USD) in damage, though more recently, it is estimated that there were $2.1 billion (1972 USD) in losses associated with the storm. Due to the significant effects, the name Agnes was retired in the spring of 1973.
In Pennsylvania, heavy rainfall was reported, with much of the state experiencing more than 7 inches (180 mm) of precipitation. Furthermore, a large swath of rainfall exceeding 10 inches (250 mm) was reported in the central part of the state. Overall, the rains peaked at 19 inches (480 mm) in the western portions of Schuylkill County. As a result, Agnes is listed as the wettest tropical cyclone on record for the state of Pennsylvania. Overall, more than 100,000 people were forced to leave their homes due to flooding. Some buildings were under 13 feet (4.0 m) of water in Harrisburg. At the Governor's Mansion, the first floor was submerged by flood waters.  Hundreds were trapped in their homes in Wilkes-Barre due to the overflowing Susquehanna River. At the historic cemetery in Forty Fort, 2,000 caskets were washed away, leaving body parts on porches, roofs, and in basements. In Luzerne County alone, 25,000 homes and businesses were either damaged or destroyed. Losses in that county totaled to $1 billion (1972 USD).  At Chadds Ford Township, the Brandywine Creek crested at 16.5 feet (5.0 m), sending flood waters into the city. Water poured into the first floor of an art museum in Chadds Ford Township, which threatened at least $2.5 million (1972 USD) in N.C. Wyeth paintings, though they were quickly moved to the upper floors.  Along the Allegheny River, it was above flood stage in some low-lying areas. During the height of the storm, the river was rising at about 7 inches (180 mm) per hour. In Reading, the Schuylkill River reached a record flood of 31.5 feet. Hundreds of people were evacuated and over a hundred homes destroyed. Floods reached as far inland as 3rd street in the heart of the city.

More than 100 Harrisburg YMCA campers and staff were evacuated using two CH-47 Chinook helicopters flown by the National Guard at Camp Shikellimy located downstream of DeHart Dam in Middle Paxton Township. Additionally, 36 Girl Scouts were rescued by state police while at a camp in York. A bridge collapsed in Danville, which caused two diesel locomotives and several freight cars to fall into a swollen creek. In the state of Pennsylvania, more than 68,000 homes and 3,000 businesses were destroyed. Due to the destroyed houses, at least 220,000 people were left homeless. The damage and death toll was the highest in Pennsylvania, with 50 fatalities and $2.3 billion (1972 USD) in losses in that state alone.
Where Sandy does seem to be unprecedented is the size of the storm surge in New York City and the resulting damage to the electrical and subway systems:
At least 660,000 people in New York had lost power as of late Monday night, the result of a higher than normal storm surge, a planned power shut-down and an explosion at a substation in Manhattan, John Miksad, a senior vice-president at Consolidated Edison said in a news briefing.

The explosion occurred on Monday evening at a substation in the vicinity of 14th Street and the FDR Drive, Mr. Miksad said. The precise cause of the blast was unknown, but Mr. Miksad said flood waters or flying debris could have been involved. It knocked out power to about 250,000 people, he said.
The Metropolitan Transportation Authority said early on Tuesday that the storm was the worst disaster in the history of the New York City subway system.

“The New York City subway system is 108 years old, but it has never faced a disaster as devastating as what we experienced last night,” said Joseph J. Lhota, the authority’s chairman, in a statement. “All of us at the M.T.A. are committed to restoring the system as quickly as we can to help bring New York back to normal.”

He outlined the extent of the damage that city workers and residents would face in the coming days:

As of last night, seven subway tunnels under the East River flooded. Metro-North Railroad lost power from 59th Street to Croton-Harmon on the Hudson Line and to New Haven on the New Haven Line.

The Long Island Rail Road evacuated its West Side Yards and suffered flooding in one East River tunnel.

The Hugh L. Carey Tunnel is flooded from end to end and the Queens Midtown Tunnel also took on water and was closed. Six bus garages were disabled by high water.
It will be interesting to see whether this has much effect on the financial system if the outages continue for an extended period.  Big financial firms have backup operations at completely separate sites (especially since 9/11): those arrangements may be about to get a test.

Our thoughts go out to all of those personally affected by this storm.


Alexander Ac said...

Hello Stuart,

regarding the precedence - what prof. Saunder had in mind was probably the combination of size AND time of year, which is unprecedented for Sandy. Normaly, so late in the year hurricanes end up in the ocean. See the dicussion on Neven's site,



Stephen B. said...

Sandy has set a new record for being the lowest pressure storm ever to make land fall north of Cape Hatteras at 943 millibars. The old record was the 1938 hurricane that moved over Long Island and into western New England.


That the winds with Sandy weren't equal with the 1938 storm probably owes to the fact that Sandy's wind field extended over a much larger area - spread out by its interaction with a strong jet stream and nearby cold front from what I understand of the situation.

Sandy actually strengthened some after moving north of Cape Hatteras, probably aided by ocean water temperatures running several degrees above average. Certainly, it didn't lose strength after moving so far north the way such storms usually do. (Gee, I wonder why the water is so warm?)

russell1200 said...

Agnes was a mess. I was younng, but all this water was dumped into these restricted channels and caused massive flooding.

If I remember, until the recent Katrina+ batch, in real dollar terms Agnes was still in the top hurricanes ever. Now it is number 8.

Stephen B. said...

From Boston TV meteorlogist, Pete Bouchard's weather blog tonight:

"After Superstorm Sandy, I think a lot of us in the weather community are asking, "what just happened?"

Certainly there will be conferences, papers and research devoted to her formation and track. The Greenland Block was a silent - but huge - player in steering her into the Mid Atlantic. Questions are already swirling around how it got so anomolously big. Could it just be happenstance, or are other forces at play? And what about her title as hurricane? Certainly other 75-80mph hurricanes aren't as vicious, nor do they carry a 10ft storm surge. Could the fact that she was a hybrid storm (part nor'easter/part hurricane) make her more efficient at generating storm surge? Lastly, what about seeing more Sandys in the future? Should we have a new classification for these types of storms? Maybe a Sub-Tropical version of the Saffir Simpson Scale?"


So the questions as I see them are, why was the Greenland block, with its associated high pressure, so strong, and why did the jet stream "dig in" and move its features along so slowly?

It seems to me that the questions Pete Bouchard is asking here fit right into the discussions you have entertained here Stuart in the past year or two, regarding more persistent Greenland high pressure and slowing Rossby waves.

That and the fact that sea surface temperatures off the Eastern Seaboard have been running several degrees above the 30 year norm which, according to accounts I have read, allowed Sandy to stay so relatively strong for so long as it moved north.

Lastly, as Pete also was digging at, this was a mighty powerful, 80 mph "hurricane." It was SO extensive area-wise, if nothing else.

clifman said...


To underscore what Alex said... apparently you overlooked the 2nd & 3rd words of your quote from the FT, i.e. "late season". Agnes was in June. This is unprecedented so late in the season. Agnes was an early season hurricane, the dynamics are very different.