What a day. On the ride into work prior to 3 AM, I pulled up a rudimentary IR loop of the East Coast on my cell phone. Though it was a three frame loop, I could see all I needed to see to realize the hybrid storm I'd been planning on was coming together - cloud tops were cooling rapidly off the coast of North Carolina, and expanding profusely. This could only mean one thing - tremendous dynamic lift was tapping the available tropical moisture and thunderstorms were firing vigorously. When I arrived at the station, I found the compact circulation of Tropical Storm Danny looking dwarfed and pathetic next to the baroclinic leaf structure that was taking off in diffluent air and cyclonic vorticity advection in advance of the upper level low that was ejecting out of the Gulf Coast and through the Carolinas.
Over the next few hours, I'd be amazed as I watched every element of this hybrid storm seem to come together perfectly. The cloud tops became so cold, as evidenced in this colorized infrared satellite image, they were off the temperature scale accompanying most normal enhanced imagery, cooling to -80 degrees Celsius, or -112 Farenheit. Multiple overshooting tops were assumed to be ongoing, and that would be confirmed by visible satellite imagery at sunrise. Soon, a central dense overcast (CDO), or shield of clouds accompanying broad thunderstorms, was present, and the new hybrid storm looked far more tropical than anything else. It absorbed Danny, and the National Hurricane Center discontinued advisories. Cooler and drier air could be seen punching in behind the storm aloft, in the subsidence associated with the Gulf shortwave, and though most of the structure of the storm was quite tropical, this was, of course, the first sign that it was hybrid. Overshooting tops become evident on visible satellite imagery - a few at first, then more numerous. 
As the storm pushed north, its tropical rains spread north with the warm and moist advection of tropical air into an antecedent fall airmass, and the closer the circulation came to New England, the more it began to interact with this baroclinicity. Winds started turning gusty - but not from the direction or in the manner I'd have thought. Our first tropical storm force gust was 39 mph at Isles of Shoals on the seacoast of New Hampshire - a northeast wind with temperatures in the 50s! The place I expected the most wind - and had forecasted damaging wind with gusts in excess of 61 mph - was Cape Cod, and after a burst of overnight pressure gradient driven wind, the wind there had gone fairly quiet, rarely gusting above 25 mph.
Then, a circulation appeared on radar south of Long Island and moving northeast. Convection was attempting to wrap up around the circulation. Perhaps this was what I'd been waiting for. It moved into the South Coast of New England, and even though the circulation was evident on radar and radial velocity plots showed fast and tight rotation, with winds exceeding 60 knots at times just off the deck by a couple of thousand feet, winds still remained below 25 mph.
It was at that point - 2:35 PM - one hour after I expected 60+ mph gusts to arrive - that I began to accept the reality that this storm probably would be remembered only for its rain, but not for any damaging wind. That's a pathetic excuse for a hybrid storm, especially one that showed all the signs of a damaging wind core on satellite this morning. I wrote a post for our NECN Weather Team blog and acknowledged the poor wind forecast, accepting responsibility for all the marina operators and boat owners and others who took precautions to ensure damage would not be done, and that I'd let them down. But, as I left the weather center and Joe would handle coverage on his own, I mentioned "watch the South Coast...those winds haven't shifted yet, so there's some sort of circulation still south of us. The surface low hasn't come through."
Within the hour, a new circulation appeared on radar. By 3:35, winds were gusting over 40 mph, and by 4 PM, damage reports were coming in. The maximum reported wind gust thus far has been 61 mph at Horseshoe Shoals, Nantucket. Thankfully, this hybrid was late to the party, but performed. It used all the stealth that a hybrid storm should - carrying its core of damaging wind on the east side of its circulation, and removed from the center by about 30 miles. Meanwhile, additional damage reports have come in from the north side of the tropical/coastal front that's been draped over Southern New England, with some damage occurring on a northeast...and in Rhode Island...northwest wind.
Truly an amazing storm. There is nothing like it. The hybrid lives on! And the damage reports/rainfall amounts as of 4 PM, compiled by NWS Taunton Skywarn, can be viewed if you continue reading this post.
Matt
