Threat of Northeast Effects from Sandy
Wow... what an extraordinarily unusual scenario. What seemed like a fluke of an idea - a hurricane-like system hitting the northeastern U.S. - is gaining credibility. Originally the European model was on its own with the spectacular but somewhat bizarre idea that Sandy would be injected with jet stream energy and curve back toward New England as a stunningly strong storm. Now one model after the other, including the ensembles, are favoring a swing back toward the East Coast after the storm goes by Cape Hatteras.
This the the afternoon run of the American GFS model ensembles - multiple lower-resolution runs with slightly different initial information, which allows for the fact that we can't measure the atmosphere precisely among other things.
The majority of the possible tracks now head into the Northeast, New England, or Atlantic Canada.
Could it really be a strong hurricane, as the European model predicts? We know that, occasionally, hurricanes do occur at these high latitudes at the end of October. Famously, the "Perfect Storm", otherwise known as the Halloween Hurricane battered New England in 1991. Also, Category 2 Hurricane Ginny hit Nova Scotia in late October 1963. But, neither were of a scale and impact like the Euro is showing.
With the influence of the jet stream, you would think any storm that comes ashore would be subtropical in nature - part tropical and part like a nor'easter - but the NHC doesn't allow for subtropical hurricanes in their naming scheme. It's considered to be such a rare and nearly impossible event.
The spectacularly unusual confluence of events is the shape and orientation of the dip in the jet stream that is forecast to develop over eastern North America over the weekend - oriented in such a way to pull Sandy inland instead of pushing it out to sea, and the presence of a strong tropical or subtropical system where it can get pulled in. That's so bizarrely unusual that I can't think of another event like it.
This kind of thing occasionally happens with nor'easters, notably the Great Appalachian Storm of November 1950 which curved in off the Atlantic and dumped 20 to 30 inches of snow over a wide area in the Mid-Atlantic and Midwest, but the odds of it happening with a system that originated in the tropics - with all of the moisture that that implies - are extremely low.
We certainly don't know that it's going to happen, and our concern at the moment is for our friends in the Caribbean and the Bahamas who will take a direct hit from a strengthening hurricane. The Florida and Carolina coasts also need to be ready to take protective action - especially boaters and people right at the coast - depending on the track Thursday to Saturday. But 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.