Monday, October 29, 2012

Sandy to bring unprecedented, catastrophic surge to Mid-Atlantic and Northeast Coast

Sandy to Generate Unprecedented Storm Surge in Northeast

Hurricane Sandy will generate an unprecedented storm surge along the Mid-Atlantic and Northeast Coast on Monday and Tuesday. In this blog post, I will answer questions I’ve been receiving about this surge event.

1.    Will Sandy’s surge really be worse than previous storms?

Sandy will likely produce a large and destructive storm surge along the Mid-Atlantic and Northeast Coast. Sandy’s track, or storm path, is unprecedented, so it’s a bit difficult to compare this storm with other surge events. Unfortunately, Sandy will approach the coast from the southeast and make landfall south of New York City. This is likely the worst-case-scenario track for New York. Surge tends to pile up to the right of the storm track, and this storm will very effectively pile up water in New Jersey, New York, and Southern New England.

2.    Is it a good sign that Sandy is forecast to “miss” New York and make landfall in New Jersey?

Sandy’s forecast landfall along the central New Jersey Coast is actually a worst-case storm track for the New York City area, at least in regards to storm surge generation. THIS STORM TRACK HAS NEVER BEEN OBSERVED IN MODERN HISTORY, so there is a lot of uncertainty as to what it means. It is very possible that a catastrophic surge will devastate the coast, especially in Northern New Jersey, New York City and Long Island, with a peak surge that could exceed 12 feet in some areas.

Keep in mind that a large hurricane like Sandy will generate very widespread and severe impacts, so it will be hard to “miss” this storm, even if the track shifts. Catastrophic storm surge may extend from the Delmarva Peninsula to Cape Cod. The exact track will not matter so much for many people, unless you manage to get on the “left” side of the storm track, where surge levels will be much lower.

3.    When should I evacuate?

Sandy has a very large wind field. This enables the storm to push a lot of water, even long before the storm approaches landfall.

Hurricane Ike was a large hurricane that hit Texas in 2008. Although the storm was only a category-2 on the Saffir-Simpson scale, its massive size enabled it to push tremendous amounts of water, flooding evacuation routes as long as 24 hours before landfall. More than 600 people had to be evacuated from the Bolivar Peninsula because they waited too long, and their evacuation routes were flooded by the time they decided to leave.

If you’re in coastal New Jersey, low-lying areas of New York, coastal Long Island or Long Island sound you may need to evacuate ASAP to avoid drowning in this event! This may be a life and death scenario for many people in coastal communities!

4.    How does Sandy’s surge height and extent compare to other hurricanes?
The Southern Climate Impacts Planning Program (SCIPP) at Louisiana State University and the University of Oklahoma has created the world’s most comprehensive storm surge database, which has now identified more than 6,000 high water marks along the U.S. Atlantic and Gulf Coasts. We’ve identified surge and storm tide levels for several major storms that impacted the New York City area. See previous blog posts for the storm track and water levels of these storms.

The major difference with Sandy is that it is taking an unprecedented track. Instead of moving northward, along the coast, the storm is forecast to take a turn to the west and make landfall in a more perpendicular fashion (coming at the coast instead of riding along the coast.) This should much more effectively pile up water in Northern Jersey, near New York City, along Long Island and Long Island Sound.

5.    What exactly is storm surge? Does that water level include waves?
A storm surge is really a dome of sea-water that is elevated. This dome may extend for hundreds of miles. The storm surge level is the height to which the sea level is raised above normal, and this height does not include waves. Think of it as a new sea level.

So if a community with an elevation of five feet above sea level is inundated with a 12-foot surge, this means the water will be about seven feet above street level. This water level does not include large, destructive waves that will pound buildings near the coast.

6.    What do you mean when you say water will be “pushed into the corner” near New York City?
The shape of the coastline can greatly increase the storm surge levels. Concave areas of coastline, which bend “inward,” generally trap storm surge and create higher water levels. The coastline near NYC curves on a sharp angle, which will greatly elevate surge levels, especially if a storm makes landfall south of NYC. However, storms usually approach NYC from the south, and curve to the east before approaching the city, making this piling up process less effective.

For our friends in the Northeast who are more accustomed to shoveling snow than dealing with hurricanes, think of this example. Do you know how snow can pile up in a corner when you have to shovel your driveway? As you push snow along and you approach a corner, the snow piles up quickly there because it has nowhere to go but up. This is very similar to what can happen in a hurricane. Sandy is pushing tons of water towards NJ and NY and this water is essentially trapped in a sharp angle of the coastline.

Hurricane Isaac generated a surprisingly high storm surge in coastal Louisiana this summer as it pushed water against a similar “corner” along the Mississippi Delta. Many people were shocked that a category-1 hurricane was able to generate a surge greater than 13 feet high. However, this large storm kept piling water up against this “corner” in the coastline, producing a devastating surge in some communities.

No comments:

Post a Comment