It was a hot and humid 4th of July weekend, so it was only natural to head to the closest beach. You arrive after battling some of the worst traffic of the year - perhaps on the New Jersey Parkway - and feel the nice ocean breeze as you sink your feet in the sand. It is time to jump in the water and cool off when... ouch! Pins and needles!? But it's July, why is the water so cold? That was the question many asked along the New Jersey, Delaware, and Virginia coasts this past Holiday Weekend... And the reason, upwelling.
Upwelling, and in particular coastal upwelling, is an oceanographic phenomenon that removes the warm (and sun heated) water at the surface away from land, and replaces it with cooler water from the depths of the ocean. The cause of this is from wind driven currents and a resulting process called Ekman transport. Essentially, it is this process that transports the warm surface water 90 degrees to the right of the wind direction (in the northern hemisphere). So, along the New Jersey Coast for instance, when there is a south or southwest wind, upwelling is almost certain to occur as the surface water gets pushed 90 degrees to the right, and out to sea. Winds were predominantly S-SW leading up to and during the 4th of July weekend, therefore the upwelling phenomenon was in full force at the expense of beach-goers.
Take a look at the sea surface temperature (SST) map at the very top for a regional view of the water temperatures on July 6th. Notice pockets of upwelling along the NJ, MD / DE, and VA coasts, as seen by the blues and greens. Zooming in on NJ with the map below, we see a more defined temperature gradient. Brrr, it was unseasonably cold along Ocean, Atlantic, and Cape May counties in New Jersey as water temperature along the beaches ran between 55 - 62 degrees F. Interestingly, there was a warm pool in Monmouth county that was much more comfortable in the 70s. As unpleasant as these cooler water temperatures may be, they are fairly common as winds are predominantly S-W throughout the summer months. On the other hand, a north or east wind will warm water temperatures along the coast. Upwelling also has other aquatic implications, including water color, the content of nutrients, and where fisherman should be looking for fish. It is certainly an interesting phenomenon, but can result in some chilly waters for those beach bound.
