Storm Team 10: Inside the development of Sunday's storm
While the signals were there late last week that we'd be getting a good thumping from the developing storm system that would impact Southern New England Sunday night, it became apparent Saturday afternoon, more than 36 hours before, that Tropical Storm Philippe would indeed be pulled in as a contributing factor.
Looking at the hard copy Guidance Models, it was clear that Philippe would get picked up by the upper air currents -- the "train tracks" for storms -- that would be whistling at 100 mph. The text guidance confirmed that, showing sustained winds at ground level of nearly 50 mph late Sunday night through early Monday morning.
Historically, when those models show a particular number for sustained winds, a rule of thumb is to double that number for gusts in a changing weather scenario. That would mean gusts OVER hurricane strength. What went on the air for the Saturday 11 p.m. show was a different, but similar, guidance model that showed gusts in the 50 to 65 mph range, plenty enough to bring down trees and utility lines:
There was a cold front pushing through the Mid-Atlantic states, heading to an upper air twist in the jet stream right over the Delmarva Peninsula (where Delaware, Maryland, and Virginia meet). It's like driving your car in one direction, then suddenly yanking the wheel to the left. The back end of your car spins outward. Where that spinning-out occurs, meteorologically, is called "cyclogenesis," rapid intensification of an area of "low pressure".
With the strong upper air flow out of the south, Tropical Storm Philippe was primed to be picked up to hitch the ride into Southern New England, absorbed into the bigger developing system, adding to the already blossoming energy. That total combination of atmospheric dynamics brought the strong winds, that toppled trees and power lines, leading to widespread damage across the area.