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)?
 Historical tide gage at Anchorage, Alaska. The figure shows the
same gage building at low and high tide. Photos courtesy of NOAA/NOS.
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 |
