How did water temperatures at the Jersey Shore go from the 70s to the 50s over the weekend? 

According to a graph showing the water temperature in Atlantic City from a NOAA reporting station, on Saturday, it dropped from 70 degrees to 57 degrees, and has not recovered all week.  

There is a process behind this known as upwelling. When warm water at the surface is replaced by cold water underneath, it can take days for the ocean to recover to the more comfortable levels.

This time of year, on average, the ocean is around 70 degrees.

Experts warn jumping into a 58-degree ocean when the air is 90 degrees can have significant health impacts and risks.