Water temperatures in Long Island Sound are nice and mild this July 4th holiday weekend. The Central Sound buoy has reached 76F several times over the last few days. Not bad for early July! Water temperatures near shore have generally been 70+ from Old Saybrook to Greenwich. Here’s a look at remotely sensed sea surface temperatures courtesy of the Applied Physics Lab at Johns Hopkins.
A couple neat things here. One, you can see the Gulf Stream well south in the Atlantic (with cool looking eddies!) and the warm water in Long Island Sound. Water temperatures are in the upper 60s south of Old Lyme east toward the Race and Fishers Island Sound. Water temperatures are in the mid 70s south of New Haven in the central Sound.
But what really jumps out on this map is the long stretch of Atlantic Coast with very cold water temperatures for swimming. If you like cold water – go south! Really! Persistent southwesterly winds for the last week have resulted in very chilly swimming from the Jersey Shore to the Outer Banks. I looked at water temperatures this morning on the Atlantic Ocean off the Mid Atlantic and here’s where they stand.
- Ocean City, MD – 60F
- Atlantic City, NJ – 56F
- Duck, NC – 60F
Ouch! You may be wondering why southwesterly winds result in colder water temperatures when the winds have brought us a steady supply of heat and humidity? The earth’s rotation (coriolis force) and Ekman Transport (due to frictional drag of the wind on the water and water on water) result in water being transported 90 degrees to the right of the wind. A southwesterly wind on the Jersey Shore will direct water offshore near the surface thanks to Ekman Transport and that water will be replaced by cooler water from deeper depths. This is known as upwelling.
If you look closely at Long Island Sound you can see some signs of upwelling along the Connecticut shoreline in that satellite image – though the impact on the Jersey Shore is much more pronounced given the long fetch of the wind over the ocean and the much, much deeper ocean waters. Another reason to love Long Island Sound beaches 🙂