The Nor'easter That Wasn't: Extratropical Cyclogenesis Without Hurricane Sandy

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Thursday, 6 February 2014
Hall C3 (The Georgia World Congress Center )
Steven G. Decker, Rutgers Univ., New Brunswick, NJ

Handout (2.7 MB)

During 29 October 2012, Hurricane Sandy underwent an extratropical transition as it approached the New Jersey coast. Interaction with a large-scale trough approaching the East Coast helped expand the wind field, leading to rough seas as far west as Lake Michigan and blizzard conditions in West Virginia. However, the most damaging impacts were felt in New Jersey and New York, as the trough interaction helped maintain winds up to hurricane force, leading to an extreme storm surge and wind damage well inland. However, one might surmise that the same factors that helped maintain the strength of Sandy during extratropical transition may have driven a strong extratropical cyclogenesis event off the East Coast had Sandy never existed. For example, were synoptic extratropical precursors conspiring to produce a blizzard in West Virginia anyway? This paper tests this hypothesis by running WRF simulations of this event with Hurricane Sandy removed from the initial conditions over the Caribbean Sea.

Starting from 00 UTC 25 October 2012, a 132-hr control run simulates Hurricane Sandy fairly well. The westward and eastward jogs in its track are similar to those observed, but Sandy makes landfall too far north, over Narragansett Bay, too intense, at 933 mb, and too late, at 09 UTC 30 October. An experimental simulation removed the vortex associated with Hurricane Sandy from the 00 UTC 25 October data, but tropical cyclogenesis immediately recommenced anyway. Therefore, additional experiments were performed. First, SSTs near Sandy were lowered such that tropical cyclogenesis was not possible. Second, relative humidity near Sandy was lowered to minimize the impact leftover Sandy moisture would have on any extratropical cyclogenesis along the East Coast.

Preliminary results show that a nor'easter does form even under the most stringent conditions for Sandy removal. The cyclone develops over the North Carolina coast, heads to Montauk Point, and then turns northwest toward Ottawa, Canada. It snows over West Virginia. However, the impacts of this nor'easter, while non-negligible, are simulated to be much less than what was observed with Sandy. This study helps to quantify the degree to which Sandy's impacts on the built environment can be attributed to the tropical cyclone as opposed to those purely attributable to the large-scale extratropical conditions.