Take a look at today’s early morning (Sept. 3, 2016) Hermine forecast track from the National Hurricane Center – NHC (Fig. 1) and you’ll see several things appear to be, well, just plain weird. However, there is some good rationale behind each of these.
First, Hermine is expected to slow down and possibly try to make a cyclonic (counterclockwise in the Northern Hemisphere) loop off the New Jersey coast early next week. This is linked to Hermine’s interaction with a developing, middle latitude, cold core, cut-off upper level low-pressure system.
Next, the 72-hour forecast indicates that Hermine will transition into a middle-latitude or extra-tropical hurricane. This, too, is linked to interactions between the upper low and Hermine. It is also tied to Hermine exiting the Carolina’s and moving back over relatively warm waters. The storm will become a hybrid with some attributes of a hurricane (wind speed core near the storm’s center) and some associated with a winter-like storm (colder central core temperatures).
Due to proximity to land, and with lessons learned from Storm Sandy in 2012, NHC will continue to issue advisories on Hermine, even after the storm becomes extra-tropical. This is to better keep public attention on hurricane dangers.
Finally, hurricanes do not usually slow down and spin within a relatively confined geographical area, once they recurve to the northeast. However, the “Perfect Storm” (a.k.a., the Halloween Storm of 1991) and Storm Sandy in 2012 (see synoptic maps animation) are among storms that have undergone a similar type of tropical/middle-latitude interaction in which a middle-latitude, upper level low “captures” the hurricane circulation.
Hermine is not done wreaking her havoc on the U.S. East Coast. She has already produced a significant storm surge and associated coastal erosion in Florida’s Big Bend region – mainly Taylor County (thanks to the storm’s track and the shape of the coastline immediately to the southeast of the storm’s path); excessive rainfall along Florida’s west coast, including nearly 20 inches in the Tampa area (Pinellas County); and widespread wind damage to homes, trees and power lines (with significant power outages – in the hundreds of thousands).
Early Saturday morning, tropical storm watches and warnings, storm surge alerts, forecasts of additional excessive rainfall and tornado watches cover at least parts of coastal locales from the Carolinas into southern New England. However, the best measure of the overall, long-term, potential impacts is the five-day graphic forecast for Atlantic City, New Jersey (Fig. 2). Tropical storm conditions (including pounding surf and storm surge) will likely cause serious coastal damage and erosion.
© 2016 H. Michael Mogil
Originally posted 9/3/16