|"Only dull people are brilliant at breakfast"
|"The liberal soul shall be made fat, and he that watereth, shall be watered also himself."
-- Proverbs 11:25
This is a beyond-strange situation. It's unprecedented and bizarre. Hurricanes almost always bend out to sea in October, although there have been some exceptions when storms went due north, but rarely. No October tropical systems in the record book have turned left into the northeast coast.
The strong evidence we have that a significant, maybe historic, storm is going to hit the east coast is that EVERY reliable computer forecast model now says it's going to happen. The only way we can forecast the weather four or five days days from now is with the aid of these super-complex computer programs run on supercomputers. The two best, the European and the U.S. GFS (Global Forecast System) run by NOAA, are now in reasonable agreement that there IS going to be an extraordinarily unusual confluence of events that results in a massive storm.
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.
At least that's what the models are saying. And since all of the independent models are saying something similar, we have to believe them and be ready.
For most people being ready means getting to the store and getting stuff before everybody else gets wise and gets the stuff first. The forecast is for an incredibly widespread and long-duration windstorm, meaning power will likely be out for an extended period of time in a lot of locations.
A transistor radio is your best friend in a situation like this. Get one and enough batteries to keep it going. Your cell phone may or may not be your friend after a big storm.
For people near the coast, it's critical that you pay attention to local evacuation orders and emergency information. This storm, as forecast, will create dangerous and potentially life-threatening storm surge along hundreds of miles of coastline north of where the center comes ashore. Big storms move a lot of water, and this one is about as big as they come.
Right now, it looks like the storm center will land between the Delmarva and New Jersey, which would put the entire Tri-State area of NJ, NY, and Connecticut on the bad side of the storm. The Jersey Shore, Long Island, and New York City itself would be exposed to the brunt of the storm surge due to the "L" in the coastline at NYC. The angle and duration of the wind will keep the water high for an extended period of time, if this comes together as forecast. This means transportation disruptions and widespread coastal damage.
During September 2012, ocean temperatures off the mid-Atlantic coast in the 5x10° latitude-longitude box between 35 - 40°N, 65 - 75° W were 2.3°F (1.3°C) above average, according to the UK Met Office. This is the 2nd greatest departure from average for ocean temperatures in this region since reliable ocean temperature measurements began over a century ago (all-time record: 2.0°C above average in September 1947.) These unusually warm waters have persisted into October, and will enable Sandy to pull more energy from the ocean than a typical October hurricane. The warm waters will also help increase Sandy's rains, since more water vapor will evaporate into the air from a warm ocean. I expect Sandy will dump the heaviest October rains on record over a large swath of the mid-Atlantic and New England.
Hurricanes are expected to dump 20% more rain in their cores by the year 2100, according to modeling studies (Knutson et al., 2010). This occurs since a warmer atmosphere holds more water vapor, which can then condense into heavier rains. Furthermore, the condensation process releases heat energy (latent heat), which invigorates the storm, making its updrafts stronger and creating even more rain. We may already be seeing an increase in rainfall from hurricanes due to a warmer atmosphere. A 2010 study by Kunkel et al. "Recent increases in U.S. heavy precipitation associated with tropical cyclones", found that although there is no evidence for a long-term increase in North American mainland land-falling tropical cyclones (which include both hurricanes and tropical storms), the number of heavy precipitation events, defined as 1-in-5-year events, more than doubled between 1994 - 2008, compared to the long-term average from 1895 - 2008. As I discussed in a 2011 post "Tropical Storm Lee's flood in Binghamton: was global warming the final straw?", an increase in heavy precipitation events in the 21st Century due to climate change is going to be a big problem for a flood control system designed for the 20th Century's climate.