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Posted at 03:15 AM ET, 10/25/2012

Mega-storm threat growing for mid-Atlantic and Northeast early next week from hurricane Sandy


Three models, three different scenarios. Left: the European model simulates a very strong storm off the Delmarva coast Monday morning with very heavy rain in the central and northern mid-Atlantic - with a projected landfall near Cape May later that day. Right, top: The GFS model turns the storm into the Gulf of Maine Tuesday night with a projected landfall near Portland later that night. Right, bottom: the Canadian model shows the storm making landfall near Boston Wednesday morning. (Stormvistawxmodels.com and MeteoCenter, Canada)
There is a consensus forming in weather forecast models that hurricane Sandy is unlikely to go out to sea. Instead, it more likely will merge with a strong fall cold front and transition into a powerhouse, possibly historic mid-latitude storm along the mid-Atlantic and/or Northeast coast Sunday through Wednesday.

The majority of models now take Sandy from its current position just west of Santiago de Cuba in southern Cuba before curving the storm towards either the mid-Atlantic or Northeast coast. Models disagree on where the storm will recurve and make landfall: simulations vary from the mid-Atlantic to Maine. There remains a chance, though diminishing, the storm will slide harmlessly out to sea.


GFS forecast ensemble members all simulate Sandy recurving towards the East Coast. (NOAA)
The location of the storm’s landfall is very important for determining exactly what local impacts will be. Not everyone will experience significant or dangerous storm conditions. But suffice to say, coastal regions from the Carolinas through eastern Canada are likely to get battered by tremendous surf and face a real risk of significant to severe coastal flooding. This storm will be a slow mover meaning large waves may pound the coast for lengthy time periods. Not to mention, the wind and waves will raise the water level, bringing ashore a multiple foot storm surge in regions close to where the storm makes landfall (assuming it does so).

Making matters worse, the storm will coincide with a full moon Monday night, meaning elevated tides above normal levels. Astronomically high tides have played a key role in historic coastal flooding events along the East Coast, such as the Ash Wednesday storm of March, 1962.

Inland areas in the mid-Atlantic and Northeast, from Richmond to Washington, D.C. to New York City to Boston, may also deal with significant storm impacts. Heavy rains are possible along with punishing winds. But the track is key in determining exactly where and we cannot say which areas, if any, will experience these conditions.

As a hurricane transitions into a mid-latitude weather system, the storm’s core tends to unwind. This means the most extreme winds around the storm’s center diminish some, but very strong winds spread out over a larger distance, affecting a much broader region. In other words, sustained winds above tropical storm force (39 mph) will be possible for locations well-displaced from the storm’s center, meaning a high power outage risk.

Severe inland flooding is another possibility. But again, it’s impossible to pinpoint if/where this will occur. Recall that the inland flooding - as opposed to wind or storm surge - was the greatest cause of death and economic damage during hurricane Irene in 2011 bringing torrents to upstate New York and Vermont.


GFS snowfall simulation for storm (Weatherbell.com)
Finally, snow may be an issue at high elevation in the interior mid-Atlantic and Northeast as cold air pours down on the storm’s west and southwest flank. Some models suggest over a foot of heavy, wet snow could fall in places like western Maryland and central and western Pennsylvania. This amount of snow on top of existing foliage could result in tremendous tree damage and power outages.

Snow is much less likely at lower elevations as the storm wraps around some mild air from the tropics. However, it cannot be ruled out briefly towards the tail end of the storm as tropical air departs and cold air wins out.

Why is the storm unlikely to go out to sea?


Simulation of blocking flow in atmosphere (Penn State)
It’s actually pretty simple: a traffic jam in the atmosphere’s flow probably won’t let it. Models are consistent in showing a “blocking” area of high pressure west of Greenland and a big ocean storm to its east. These features are likely to prevent the big incoming cold front from pushing Sandy out to sea. The North Atlantic Oscillation - a measure of this “block” in the flow, is forecast to be three standard deviations from the average- meaning this is an exceptional situation. Thus, the storm is favored to be forced north rather than going east out to sea (although I stress this still cannot be ruled out)

As NOAA’s Hydrometeorological Prediction Center writes:

“THERE IS INCREASING CONSENSUS AMONG THE GUIDANCE FROM THE VARIOUS MODELING CENTERS... THE ENTIRE ATLANTIC BASIN SEEMS DESTINED TO BECOME DOMINATED BY BLOCKY HIGHS AND LOWS, WITH DECREASING WIGGLE ROOM FOR EVEN LARGE FEATURES LIKE SANDY. ”

Round-up of voices/opinions about this storm

Jeff Masters, wunderground: “Sandy: a potential billion-dollar storm for the mid-Atlantic and New England”

Dr. Greg Forbes, the Weather Channel: “A worst-case scenario of Hurricane Sandy or some hybrid (mixed with a cold front and jet stream system coming toward it) could bring a widespread destructive windstorm to some part of the Northeast from Sunday into early next week. Prior to then, heavy rain, strong gusty winds, large waves and maybe storm surge are possible for coastal areas from FL to NJ.”

Bryan Norcross, the Weather Channel: “....it’s not often that credible forecast models consistently forecast a historic event, and with more models leaning that way, we need to be aware and pay attention along the entire U.S. East Coast.”

Joe Lundberg, AccuWeather: “....the evidence seems to be mounting toward the convergence of these two weather systems into an historic storm early next week.”

Alex Sosnowski, AccuWeather: “The realm of possibilities continues to range from Sandy escaping out to sea, with nothing more than blustery, much cooler air sweeping in, to a dynamic storm turning inland packing coastal flooding, flooding rainfall, high winds, downed trees, power outages, travel mayhem and even Appalachian snow.”

By  |  03:15 AM ET, 10/25/2012

 
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