Updated: Hurricane Sandy likely to hit mid Atlantic - could be "Perfect Storm"

NHC's 5pm forecast brings Sandy into the Jersey shore Tuesday morning then inland to Pennsylvania by Tuesday evening. Sandy's strongest winds, storm surge and waves could affect highly populated northern New Jersey and New York City. The full moon and high tides will increase impacts to New York harbor, beaches and coastal communities.

The NHC forecasts hurricane Sandy to landfall on the U.S. east coast in 120 hours. Hurricane Sandy maintained most of its integrity and strength while passing over Cuba and is about to strike the south central Bahama Islands with 105 mile per hour (about 90 knots) sustained winds. Winds aloft continue to be very strong - 126 knots at about 10,000 feet - but the low level circulation and eye were disrupted by Cuba's high terrain.  microwave and visible imagery shows that the eye reforming over the warm waters between Cuba and the Bahamas.
Both the intensity and track forecasts are problematic. A large wave in the upper atmosphere over the continental U.S. has started to interact with Sandy. The models that forecasters use to predict both the track and intensities of hurricanes have been in consistent disagreement for several days. The reliable European ECMWF model has consistently tracked Sandy towards the mid-Atlantic states and maintained Sandy as a very intense storm. The good GFDL (Geophysical fluid dynamics lab) model has aligned with the ECMWF forecast for the past 2 days. This morning, the HWRF model finally fell in line with the mid-Atlantic landfall prediction. The general agreement of these 3 models forced the NHC to adjust its forecast westward towards New Jersey in 5 days.

The hurricane center is forecasting shear to weaken Sandy but so far Sandy has been insensitive to 20 knots of shear. That's probably because the shear isn't reaching Sandy's core. The upper winds around Sandy are spreading apart - they are highly difluent - and the shear calculations don't account for this difluence. These interactions with an upper atmospheric wave give Sandy some frontal characteristics. Sandy is no longer a "pure" tropical storm.

Professor Robert Hart of Florida State University has developed a way to analyze hybrid storms that have both tropical and frontal characteristics. His model shows Sandy becoming a deep hybrid low as it moves north of the Bahamas tomorrow. It will become like Hurricane Irene, a deep low with a broad wind field and a large storm surge according to multiple FSU model runs. The latest GFDL model analysis shows a broad deep low, a perfect storm, landfalling near Delaware Bay. The National Hurricane Center is forecasting just below hurricane strength winds as Sandy approaches shore, but because Sandy will likely be a very large storm with deep low pressure and a large storm surge, it will likely cause far more damage than a pure tropical category 1 hurricane.

Sandy is a potential billion dollar storm if it makes landfall on the mid-Atlantic (or New York City & Long Island).

The mid-Atlantic U.S. scenario
Landfall Monday along the mid-Atlantic coast on Monday, as predicted by the ECMWF and NOGAPS models, would likely be a billion-dollar disaster. In this scenario, Sandy would be able to bring sustained winds near hurricane force over a wide stretch of heavily populated coast, causing massive power outages, as trees still in leaf fall and take out power lines. Sandy is expected to have tropical storm-force winds that extend out more than 300 miles from the center, which will drive a much larger storm surge than its winds would ordinarily suggest. The full moon is on Monday, which means astronomical tides will be at their peak for the month, increasing potential storm surge flooding. Fresh water flooding from heavy rains would also be a huge concern. Given the ECMWF's consistent handling of Sandy, I believe this mid-Atlantic scenario has a higher probability of occurring than the Northeast U.S. scenario. However, it is likely that the models are overdoing the strength of Sandy at landfall. The models have trouble handling the transition from tropical storm to extratropical storm in these type of situations, and I expect that the 940 mb central pressure of Sandy predicted at landfall Monday in Delaware by the ECMWF model is substantially overdone.

This storm scenario reminds me of the typhoon systems that turn extratropical in fall over the Pacific Ocean, delivering massive swells to the Hawaiian Islands. As the hurricane season extends later into the fall in the Atlantic, as it appears to be doing according to a recent post by Jeff Masters, we can expect to see an increase in "perfect storms" affecting the east coast of North America. This is an unprecedented third year in a row with 19 named storms.  The Atlantic waters on the east coast of the U.S. and Canada have been at record levels this summer and fall. This record ocean heat sets the scene for a perfect storm.
Multiple models predict Sandy will be a "perfect (hybrid) storm" to hit the east coast early next week.Update
Note the large "blocking high pressure" extending across the north Atlantic south of Greenland. This large dome of relatively warm air and high surface pressure will develop an east to west flow that will turn Sandy back towards the east coast. This is from the midday 12Z run of the GFS model today, Oct, 25.