A windy Long Island Sound? The meteorologists at Sailflow often chuckle at this oxymoron, as Long Island Sound winds tend to be much weaker than most other areas of the Northeast. There are many reasons why anemometers rarely  turn at high rpm on this body of water, but the key factor is Long Island itself.

The image on the left shows a slightly exaggerated relief map of Long Island Sound, which sits in a basin with hills on 3 sides. Tidal currents are strong through the Sound, which keeps water temperatures on the cool side.    With a primarily south and southwest synoptic (large scale) wind, we experience what the Canadians call "doming," also known as  "decoupling." Doming is when warm winds don't want to mix to the surface over cool waters.  

That's not to say that southerly and southwesterly flow never occurs on Long Island Sound, but the flow is often weaker than forecasters and forecast models predict. Winds tends to be spotty and shifty when the flow does occur. It is not uncommon on these decoupling days to see flags and trees rustling inland, only to find light conditions on the water.

Because it is exposed to the east, Long Island Sound is susceptible to nor'easters and stalled fronts, which can channel an easterly flow down the Sound. These are the strong wind directions that forecasters often under predict. It is also common for an easterly flow to hang around longer than models anticipate.

SailFlow

Graphs show wind velocity from the 2006 Marblehead NOOD. The colored lines represent windspeed over time; the yellow arrows represent wind direction over time

The 2006 Larchmont NOOD saw a weak, prevailing northerly gradient that was undercut on Day 1  by a weak southerly sea breeze. On Day 2, the wind shifted more to the northeast; notice on the graph how the winds were able to hold out much of the day and never turned southerly.  

What about this year's regatta? Last weekend we saw a light southerly trend then a stronger southwest breeze arrived on Labor Day as a weak frontal boundary slipped onto the region. As expected, the Labor Day wind was patchy and shifty. Long range models show high pressure moving offshore into the weekend, which places the region in a southerly flow. With good sunshine the wind likely will tend to pulse with increasing velocities and more frequent right shifts from south to south-southwest through the afternoon. Keep an eye on the coastal low developing off of Georgia, as it could bring on an easterly flow if it holds together and slips north as some computers suggest. Tough call, so stay on it at www.sailflow.com.

Knowing what forces are driving the winds is of great importance to gaining the edge on your competition.  Sailflow.com provides real-time sensors as well as forecast products complimentary through the race period at http://www.sailflow.com/Larchmont

In cooperation with North Sails, Sailing Weather Service is offering free precision race forecasts for this event.  Sign up at http://na.northsails.com/ew/ew_main.taf