Strangely Different Tides

Q: Why is there such a difference (30 to 60 minutes) between high-tide times for two neighboring coastal cities (for example, Atlantic City and Cape May, NJ — only 15 miles apart)?

A: This is a curious phenomenon. The Moon and the Sun pull on Earth and cause tides.

We don't expect astronomically-caused events happening at essentially the same place to happen at different times.

The tide gage at Atlantic City is on the oceanfront. The Cape May gage is 40 miles away at the ferry. (not at the 15-mile distant city of Cape May).

"A tidal difference of 30 minutes is not unexpected for two locations separated by that much distance," says the Tide Predictions branch of the National Oceanic and Atmospheric Administration.

Dean Iovino of the National Weather Service, however, brings up another example: "It takes the high tide about six hours [about three times longer than expected] to travel from Cape May... [up] the Delaware River to reach Philadelphia, a distance of about 90 miles (by water)."

That's it. Confining land and shallow water slow the tides.

Further Surfing:

Tides & Currents, NOAA

The National Weather Station at Philadelphia/Mt. Holly, NJ

(Answered Nov. 1998; updated Oct.17, 2007)