Matt Noyes at NECN confirms what North Shore and Cape Ann ocean swimmers already know: Brrr.
The cooling ocean water really became noticeable after the first week of July as two phenomena occurred back-to-back to send water temperatures spiraling. First, a feed of colder water sliding south down the Maine coast surged along the Cape Ann shoreline and entered Boston Harbor from the north. Interestingly, ocean currents helped the water miles offshore recover fairly quickly over the last two weeks, but closer to shore, not only was a cooler pocket of water trapped, but a new phenomenon took hold: upwelling. Upwelling is a common occurrence for any coastal community near the open ocean – when the wind blows from off the land, usually a northwest, west or southwest wind in New England, that wind pushes the skim of relatively shallow, milder ocean water out to sea. The void left behind near the shoreline has to be replaced, so new water rises up from deeper, colder ocean levels to replace it, causing a drop in water temperature near the shoreline.
Confirmation of his confirmation comes from Hkergrrl, who went for a swim yesterday:
Just got back from nahant and can confirm that it is still wicked cold in the water... Pleasant at first and then completely numbing