When the heat is at its hottest, the summer ocean temperatures can often be at its coldest.
Whether your a local who has a quick drive (or walk) to the beach, or somewhere traveling the Garden State Parkway, Atlantic City Expressway or Route 55 over the shore, getting the feeling of pins and needles when you hit the water on a day when the sand is scorching puts the damper on any beach day. However, upwelling brings benefits to marine life and yes, those who really need to cool down.
Coastal upwelling is the process at which the top layer of the water, which is sun heated and the warmest layers, moves away from land. Deeper, colder ocean water then replaces it. The cause of this is from wind-driven currents and a resulting process called Ekman transport.
Ekman transport moves warm surface water 90 degrees to the right of the wind direction in the northern hemisphere. This is due to the Coriolis effect (the explanation will be sparred, but you can read more about it here). Taking southern New Jersey, for example, a south to southwest wind will push that water well offshore. The speed of the wind and well of the duration of the south to southwest winds will also play a role into how cold temperatures will go.
There is also such thing as downwelling. Winds from northeast or northerly direction will actually push that warmer water from the Gulf Stream to the coast at a 90-degree angle. So some of the Jersey Shore's coolest days during the summer also bring the warmest water.
While some beachgoers may not like upwelling, fishermen find it favorable. The colder water brings more nutrients up to the surface, which brings more fish along with it.