'Hurricane' Schwartz: Crazy Shore water temps explained

RECORD SET LAST WEEK

Since the ocean warms more slowly than the land, the highest water temperatures occur, on average, in late August. Last Wednesday, the ocean temperature off Atlantic City reached 83.3 degrees for a short time and it set a  record.

Jim Eberwine, a meteorologist formerly with the National Weather Service, has kept detailed air and water temperatures for the Jersey Shore for decades.  He sent some data.

Here is Jim's chart for water temperatures in various parts of New Jersey (top) and Delaware/NJ (below):

Last Wednesday was the first day in our most extreme heat wave of the year. By the weekend, air temperatures reached well into the 90s, and the humidity jumped to its highest level of the summer so far.

Yet the ocean temperature plunged. It fell from that 83.3 degrees Wednesday to 64 Sunday. I warned viewers about the coming drop. So what caused it, and how did I know?

Because we've seen it all before.   The change is brought about by upwelling, which happens occasionally in summer under certain conditions.

At the Jersey Shore, upwelling involves a persistent wind from the Southwest. While that wind direction heats up inland areas, it is parallel to the shore. That causes the warm surface water to get pushed out to sea. And to replace it, colder water from below moves up to the surface. Here's a graphic and explanation from NOAA.

I've seen ocean temperatures drop into the 50s in the middle of summer on some of the hottest afternoons on land. It happens every year, and there's nothing unusual about it.

WILL THE WATER GET WARM AGAIN?

In a word: yes. A persistent wind from the East or Southeast will allow some of that warmer water to return. But it may not get back to the record 83.3 degrees, or maybe not even 80. That's a temperature uncommon for the Jersey Shore, but a bit more common for the Delaware beaches.

Glenn "Hurricane" Schwartz
Chief Meteorologist, NBC10 Philadelphia