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Posted at 02:37 PM ET, 08/26/2011

For Northeast, Hurricane Irene poses a rare and very real threat

Hurricane Tracking Center with Tweets from NHC
Q&A transcript: Prepare for Hurricane Irene
Live updates: Follow the storm all day
Tropical Storm Warning for most of D.C. metro area
Hurricane Warning for Va/Md/De Beaches
Irene: Are You Prepared?
Live webcams of East Coast beaches
Federal Eye updates

Millions of people from Philadelphia northward to Maine are bracing for what may be their closest encounter with a hurricane since at least 1991. Depending on the exact path and strength of Irene at its closest pass, the storm has the very real potential to sock New Jersey, Southeastern New York, Connecticut, Rhode Island, and Massachusetts with the region’s fiercest hurricane or strong tropical storm in many years. In fact, most New Yorkers have never seen a hurricane pass over or just to the west of the city, a track that would bring a dangerous storm surge into highly populated and pricey real estate.

Even if Irene loses some of its punch as works its way up the coast, moderate to major impacts — including flooding, downed trees and significant power outages — are still anticipated in the heart of the urban corridor from Philadelphia to Boston, especially near and east of I-95.

As detailed by New York City’s Department of Emergency Management, most of the hurricanes that have caused damage in the city have passed east of Manhattan, over Long Island or Southeast Massachusetts. There was a hurricane that made a direct hit on Manhattan in 1821, however. That example does not bode well:

“The tide rose 13 feet in one hour and inundated wharves, causing the East River to converge into the Hudson River across lower Manhattan as far north as Canal Street. However, few deaths were attributed to the storm because flooding was concentrated in neighborhoods with far fewer homes than exist today,” the city Web site states.

The deadly 1938 hurricane – the benchmark against which all New England hurricanes are measured – passed about 75 miles to the east of New York. Still, that storm, which made landfall as a Category 3 monster, managed to kill 10 people in New York City. As the NYC emergency management Web site notes: “The hurricane could have caused far more deaths and damage if it passed closer to the five boroughs.”

The worst-case scenario for New York would involve Irene tracking over or just west of the city at hurricane strength, since that would expose the city to the greatest winds and storm surge on the storm’s eastern side. If Irene tracks to the east of the city (crossing Long Island) and/or as a strong tropical storm rather than hurricane, the winds in the city would be weaker.

However, the storm will still push a large wall of water up the East Coast. As early as last night, the New York City office of the National Weather Service was warning of “A DANGEROUS...LIFE THREATENING STORM SURGE MAY EVEN BE POSSIBLE SUNDAY EVENING... ESPECIALLY IF THE SURGE COINCIDES WITH HIGH TIDES...WHICH ARE RUNNING HIGHER THAN USUAL DUE TO THE NEW MOON ON FRIDAY.” While Irene has weakened a bit since, the NYC NWS office is still calling Irene “LARGE AND DANGEROUS” with the worst of it likely late Saturday night into Sunday afternoon:

“THERE IS INCREASING CONFIDENCE IN TORRENTIAL RAINS DEVELOPING OVER THE REGION SAT NIGHT AND CONTINUING THROUGH MUCH OF SUNDAY BASED ON THE NHC FORECAST TRACK FOR HURRICANE IRENE. A PRECURSOR LOCALLY HEAVY RAINFALL EVENT COULD TAKE PLACE SAT IN THE VICINITY OF A NORTHWARD DRIFTING REMNANT FRONT WELL BEFORE THE ARRIVAL OF VERY HEAVY RAINS ASSOCIATED WITH THE HURRICANE ITSELF. STORM TOTAL QPF OF 5 TO 10 INCHES IS LIKELY FOR MUCH OF THE REGION...WITH LOCALLY UP TO 15 INCHES DEPENDING ON THE EXACT TRACK OF THE STORM.”

Many parts of New York City and nearby parts of New Jersey are extremely vulnerable to coastal flooding, including parts of Brooklyn, Queens, Lower Manhattan and Hoboken, N.J.

The storm surge will be a key concern in other highly vulnerable parts of Southern New England, from Long Island to Maine. Anyone who has ever taken an Amtrak train between Washington and Boston has seen the low-lying portions of the Connecticut and Rhode Island coastlines, and the many homes that sit along the shore there.

Boston and Providence are other major urban areas at high risk of seeing hurricane-force or high-end tropical storm-force winds and coastal flooding, again depending on the exact track, strength and timing of the storm. Like New York, there are many parts of the Boston metro region that are susceptible to coastal flooding (including my hometown of Swampscott, on the North Shore). If the storm tracks to the east of New York City, but remains west of Providence and Boston, then the latter two cities could receive the brunt of its strong winds, along with a higher storm surge.

Historical Analogs


Track and rainfall totals from Hurricane Gloria in 1985.
Some computer model projections take the storm on a path that would hug the New Jersey coast, and head right up into the Big Apple, somewhat similar to 1985’s Hurricane Gloria. Others suggest a track more offshore, similar to 1991’s Hurricane Bob, which was the last hurricane to make landfall in New England.

Hurricane Gloria made landfall on Long Island as a minimal hurricane that was undergoing a transition to an extratropical storm system. Despite traveling very quickly – much faster than Irene is projected to move – Gloria still managed to drop very heavy rainfall along and to the west of its path.

Hurricane Bob, a Category Two storm, raced from Buzzard’s Bay into the Gulf of Maine, bringing the most severe impacts to Cape Cod and the Islands, with significant wind damage all the way to Boston and the Maine coast. Hurricane-force wind gusts were recorded in many areas east of the Connecticut River. According to the National Weather Service, Hurricane Bob caused $680 million in damage, and killed six people. Bob, which was perhaps the most innocuously named hurricane on record, caused a storm surge of 5 to 8 feet along the Rhode Island shore, and drove a surge of 10 to 15 feet into Buzzards Bay. According to the Weather Service:

“The highest surges, of 12 to 15 feet, were observed in Onset, Bourne, Mashpee and Wareham, at the head of Buzzard’s Bay. Cove Road, in Mattapoisett, Massachusetts had 29 of 37 homes destroyed, while Angelica Point, Massachusetts lost 32 of 35 homes along the shore.”

Every hurricane is different, so even though Irene’s path may end up being somewhat similar to Gloria, Bob, or other storms of the past, its effects are likely to be distinct.

For one thing, its wind field is expected to be more expansive than most hurricanes and tropical storms as it approaches the coast, meaning that even points well to the west of the eye can expect damaging winds. Also, it is going to be moving slower than most storms do when they get this far to the north, because the jet stream is located along the U.S./Canadian border, and won’t be scooping this storm up and spitting it out very quickly. This will allow Irene to drop copious amounts of rainfall, which is something the mid-Atlantic states and New England do not need right now.


(NATIONAL HURRICANE CENTER)
In fact, inland flooding is the deadliest threat from hurricanes, and Irene may, unfortunately, continue to demonstrate this. Areas that are bracing for Irene have already seen an extremely wet August, with many rounds of thunderstorms leading to urban and small stream flooding. Philadelphia is going to set its record for the all-time wettest month, having already set a new benchmark for its wettest August. Earlier this month, New York’s JFK Airport set its all-time record for the wettest 24-hour period, when 7.8 inches fell Aug. 14.

The wet conditions mean that there is a greater likelihood for inland flooding with Hurricane Irene than there otherwise would be, and it also primes the region for significant tree damage from even just tropical storm-force winds.

According to NWS forecasts, Irene is expected to dump nearly a foot of rain along and to the west of its path as it moves up the eastern seaboard and into New England. So even if the storm jogs east of New York City, there still could be major flooding problems for the city and surrounding areas to contend with.

By  |  02:37 PM ET, 08/26/2011

Categories:  Latest, Tropical Weather

 
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