Here’s an ugly graphic showing just how wet our computer models show this storm being!
I’ve included the several of our computer models from today in this graphic. The NAM, GFS, and SREF (short range ensemble forecast) all point toward a significant amount of rain. The NAM (a non-hydrostatic model prone to exaggerate precipitation in some cases) shows a wide swath of 3″+ and even 4.5″ in some location. What’s most impressive is the SREF – which shows a fairly tight clustering in its members of between 2.0″ and 3.5″ – a good signal for a soaker.
So what’s going to cause all this rain? A very strong band of convergence will set up over Connecticut later tonight and early tomorrow.
While the NAM may be exaggerating the specifics the high resolution really accentuates the features that will lead to heavy rain. Notice the bottom left panel showing winds near the surface. Over 40 knots as close as Montauk and less than 10 knots over the Berkshires. That is an incredible amount of convergence along the front which can be seen in the temperature plot in the upper left (60 near New Haven but near 32 around Binghamton, NY).
The convergence is even more pronounced here at 925 mb on the NAM a little more than 2,000 feet above the ground.
Very impressive signal here for ripping rain! A lot of this strong convergence in low levels is a response to strong divergence in the right entrance region of the 160 knot jet streak over southern Quebec.
The strong low level jet and associated divergence aloft and convergence near the surface indicates very strong lift over the region. Given the strong signal for lift and anomalously high moisture content (Precipitable water >3 standard deviations of normal) it’s time to hoist the sultan signal for heavy rain with 2″-4″ of rain likely.
As for damaging winds – I think the threat is fairly low here in Connecticut. The core of the strongest winds looks to remain south and east of our area but right along the coast from Bridgeport to Stonington I wouldn’t be shocked to see a 50 mph gust. Inland, winds will drop off quickly.