Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne One Daily Tide vs Two
Name: Mary
Status: Other
Grade: Other
Location: WA
Country: United States
Date: August 2007


Question:
On February 9, 2004, Laura asked why Panama City, Florida had only two tides a day. David R. Cook answered that there are two low tides and two high tides everywhere. I was born and lived in Panama City until I left for college. The local newspapers only recorded one low and one high tide a day. If only two are recorded a day, would not the other two tides simply be so small that they are not measured? I know there appears to be only two a day in Panama City, Florida. Can someone explain this observation?



Replies:
Mary,

When I made the statement in my entry, unfortunately I was looking at Panama City Beach, not Panama City.

Please let me clarify.

If you go to the web site

http://tbone.biol.sc.edu/tide/sites_allalpha.html#P

you can scroll down to 2 listings of tides for Panama City and 2 for Panama City Beach. Note that only one low tide and one high tide are shown for both locations on August 1. For August 2, 2007, two high and two low tides are shown for Panama City Beach and only one of each for Panama City. Panama City Beach normally only receives one high and one low tide per day. The position of the Sun, Moon, the N/S or E/W orientation of the coastline, whether the location is on the ocean or in a bay (such as Panama City in St. Andrews Bay) or in an enclosed or mostly enclosed gulf, such as the Gulf of Mexico, local underwater topography, water depth, etc. determine whether there are two observable or significant high and low tides or just one of each, and the timing of the tides at a particular location.

In general, there is one dominant high energy tide per day, at any location; this occurs typically 1 to several hours after the Moon sets at your location (this one has the greatest tide height).

A smaller energy tide (with lower tide height) occurs several hours after the Moon rises. The size of the tides and timing is dependent on the position of the Sun also.

East and west facing locations directly on the large oceans (Atlantic, Pacific, etc.) consistently experience two high and low tides per day because the path of the tide is not hindered.

If your location is within a bay with a narrow opening, such as is the case of St. Andrews Bay for Panama City, it takes a long time for the bay water level to respond to the high energy high tide in the Gulf of Mexico; note that the Aug 1, 2007 Panama City high tide occurs some 2 to 3 hours after the Panama City Beach high tide. St. Andrews Bay then starts emptying, working towards low tide, but, again, it is delayed in doing so by the narrow bay opening and so Panama City experiences low tide hours after Panama City Beach.

Only 5 hours later, on August 2 early morning, Panama City Beach has low energy high and low tide within a couple of hours of each other (2:47 and 4:44 respectively), which are hardly different in height. It's impossible for St. Andrews Bay to respond to these quick and small tide changes, so the low energy high and low tides simply do not occur at Panama City. In reality, the low energy high tide serves only to keep the water level in St. Andrews Bay higher overall between high energy high tides, than would occur if it could respond to the low energy tide.

Computer models are used to determine tide tables because of the complexity of the physical considerations, such as occurs at Panama City.

David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory



Click here to return to the Environmental and Earth Science Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory