Model simulations have consistently simulated minimum pressures below 950 mb, which would be the lowest on record in many areas.
“MODELS SHOW PRESSURE WELL BEYOND WHAT HAS EVER BEEN OBSERVED NEAR THE NJ/NY COAST (EVEN EXCEEDING THE 1938 LONG ISLAND EXPRESS [HURRICANE])”, writes NOAA’s Hydrometeorological Prediction Center (HPC).
Connecticut meteorologist Ryan Hanrahan noted there has only been one tropical storm with the pressure below 960 mb in the last 60 years in the Northeast.
Bob Henson of the University Center for Atmospheric Research adds:
While a couple of hurricane landfalls in Florida have produced pressures in this range, most cities in the Northeast have never reached such values, as is evident in this state-by-state roundup. The region’s lowest pressure on record occurred with the 1938 hurricane at Bellport, Long Island (946 hPa).
In the mid-Atlantic region, here are some record low pressures, which could be blown away - depending on the track of the storm:
Baltimore: 971 mb
Richmond: 966 mb
NOAA’s HPC cautions that sometimes models lower pressure in these storms too much, and favors Sandy to bottom out near 965 mb on its approach to the East Coast - which would still be in record territory in many areas.
You might ask yourself, aren’t hurricanes supposed to weaken as they head north? Why are these pressures so low? Or as the Weather Channel’s Bryan Norcross put it: “What the hell is going on?”
Norcross’ answer: “This is a beyond-strange situation. It’s unprecedented and bizarre.”
He then offers a hypothesis (which I agree with):
The upper-air steering pattern that is part of the puzzle is not all that unheard of. It happens when the atmosphere gets blocked over the Atlantic and the flow over the U.S. doubles back on itself. Sometimes big winter storms are involved.
The freak part is that a hurricane happens to be in the right place in the world to get sucked into this doubled-back channel of air and pulled inland from the coast.
And the double-freak part is that the upper level wind, instead of weakening the storm and simply absorbing the moisture - which would be annoying enough - is merging with the tropical system to create a monstrous hybrid vortex. A combination of a hurricane and a nor’easter.
A simpler explanation: the clash of the cold blast from the continental U.S. and the massive surge of warm, moist air from Hurricane Sandy will cause the storm to explode and the pressure to crash.
These historic low pressure levels simulated by the model are equivalent to a category 3 or 4 hurricane, which have peak winds over 115 mph. But Sandy’s winds will not be that high, because as it transitions into this hybrid hurricane-nor’easter, its core will unwind. So its peak winds will diminish, but strong winds will be felt over a vast area. Think of a compressed slinky expanding as you let it go.
WJLA meteorologist Ryan Miller notes 66,549,869 people live in the National Hurricane Center’s track zone for Sandy. A large percentage of these people will likely contend with tropical storm force winds - 40-60 mph, if not somewhat greater.
I’ll conclude with this note posted in the blog by AccuWeather senior Vice President Mike Smith:
A very prominent and respected National Weather Service meteorologist wrote on Facebook last night,
I’ve never seen anything like this and I’m at a loss for expletives to describe what this storm could do.