South and SW gradient winds have a seriously hard time reaching the surface along the Connecticut coastline due to the topography of Long Island and the quite cool waters of Long Island Sound.   Usually the southerly flow is a warm flow and thus the winds decouple over the waters and land inland.   Not uncommon for a general wind forecast to call for some cranking SW winds and the flags will be fluttering inland and soon as you get to the coast, it’s glassy.

When does a southerly wind blow on the CT coast?   Not often.   However, one rule of thumb we have developed has to do with getting rid of the marine layer to allow the sea breeze to tap into the stronger winds aloft.    If you see a morning NW flow from a synoptic breeze, it can often scour out that cold marine layer as well as set up some circulation which is critical for the sea breeze to maintain a steady flow.

Today we had such a day so I captured a few images:

Modeled SLP for the morning and afternoon (note not much gradient winds at all until late in the day):

12hrfx 24hr fx

Below note the topography of the region with the hills along the coast.  This model/obs imagery shows the morning NW flow in place at 9am which is helping to scour out the marine layer a bit and setting the scene for a steady afternoon southerly:

9am topo forecast

Next, look at the graph of Hammonasset which rarely sees the steady southerly.  Note the morning NW flow that drops out and is abruptly undercut by the sea breeze, and how steady the sea breeze is (not oscillating):

Hammon northerlies

Finally, look at how the entire eastern CT coastline is seeing this steady breeze continue to rise with the good sunshine and thermals helping to drive the engine:

CT snap sat

Prepared by:

Matt Corey

Meteorologist, etc.