Rick Whorwood has asked me about understanding tides with respect to fly
fishing the Florida Keys flats. I thought my answers might be of interest
to those of you who have done that or are anticipating doing so on your own in
the near future. This is way more information than you might need unless
you are going to try to fish these areas on your own.
Our more seasoned flats guides have learned these lessons well. Years
ago, I learned by observation and trial and error. (Spent many a night stuck on
the flat in doing so.)
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Rick..........
The best tide book by far is entitled: "2007 TIDE TABLES, HIGH AND
LOW WATER PREDICTIONS, NOAA, EAST COAST OF NORTH AND SOUTH AMERICA INCLUDING
GREENLAND."
This book has an excellent description of tides and much detailed tidal
related information including the all-important moon phase relationships, tidal
and nodal constants and differences, etc. It lists for under $
20.00. Important is the fact that it gives the exact predicted heights of
each tide ... not just whether the tide is high or low.
Rick....
Some of the most important tide information cannot easily be placed in
print.....but exists in my brain after fishing these waters for almost 50
years.
For example: The tide chart may show a 2.0 high tide at 1500 hrs. at
Big Spanish Key on a particular date.
On that morning, we get a 20 knot South wind along with a barometric
pressure of 30.2".
The result is that the tide won't peak until damn near 1700 hrs. Not only
that, it won't peak with high water stand beyond a 0.7 high !
Translation: In the event I go by the tide tables, I'll arrive at Big
Spanish Key at 1500 hours expecting a high tide of 2.0 but I'll run aground
there because the tide will be 2 hrs. later than predicted because of that wind,
and 1.3 ' lower than predicted because of the barometric pressure shift.
In short, I'll arrive at relatively low tide in dramatic contrast to what the
tide tables told me.
The opposite can occur, too. Rules of thumb:-
1.) Average barometric pressure ( say... 29.92 and
steady) the effect to change the tide height is 0.
2.) High pressure = tide heights lower than
predicted by the tide tables. (This was the situation on March 3rd when
you and I and Jim Valle ran aground coming out of the Content Passage after our
Spey Casting lessons on the flats between the islands. We had very high
barometric pressure and glare-viz.)
3.) Low pressure = tide heights higher than
predicted by the tables.
4.) Strong off-shore winds = Much lower tidal
heights than predicted. (In some areas where the flats are very extensive,
the predicted incoming tide won't come in at all. If the strong winds
continue, they may hold off the incoming tide for several days
! (I remember one time years ago when Bob Andreae got stuck
up in Hell's Bay when a strong North wind blew all the water off the flats at
Flamingo. The tide didn't come in for a week at which point he could get
his boat out of there !)
5.) Strong on-shore winds = Much higher tidal
heights than predicted by the tables. This is especially true of areas
with extensive flats. (Not as much effect with deep water near the
shoreline.)
6.) Air temperature = Hot air provides
lower atmospheric density and reduces the wind effect. The opposite
pertains, as well.
Here in the Florida Keys, we have a semi-diurnal variation. It is due
to the close proximity of two oceans .. the Atlantic (Straits of Florida) on one
side and the Gulf of Mexico on the other.
This results in most of the tide coming in and going out with respect to
the ocean on one side of the Keys, and with respect to the Gulf on the
other.
We may have outgoing tide on one side, and incoming tide on the other with
only 12 miles in between .... about 4 hrs. difference between the tide on the
Ocean side and that on the Gulf side. Sometimes as much a 7 hours
difference.
This also gives us one high high tide and one low high tide each day along
with one low low tide and one high low tide each day. (Most of the best
flats fishing occurs when a high high tide follows a low low ... because that is
when the best tidal flow is found.)
Much of our fishing is done in between the islands... some nearer to the
Ocean and some nearer to the Gulf. There is a nodal point in between where the
tide shift is equal with respect to the effect of each body of water.
PROBLEM IS THAT THIS NODAL POINT IS CONSTANTLY SHIFTING WITH RESPECT TO
TIME. It is this problem which makes fishermen
throw up their hands in despair as they try to figure out the tides at any one
point in between.
When we fish near or in channels, we must learn about the differences
between high and low water stand and
high and low water slack.
Slack means that the tidal currents have ceased. Stand refers to the
extreme of tide depth, either high or low. We may, for example, have a
high water stand where the tide will get no
higher. Despite this, the tidal current will be coming in continuously for
as long as 2 hours in some areas before we reach high water
slack. We sometimes even have a
paradoxical tide where the water will be coming in,
yet the tide level is falling ! That is due to the tidal lag
produced by the fact that the extensive flats in our back country
take longer to drain and fill.
For almost 50 years, I have been watching these tidal movements and
"recorded" them in my brain as I watched the shift of the many trap buoys
(during lobster and crab seasons) as I made countless trips between the two seas
on my fishing trips. I, also, took careful note of the wind directions and
intensity as well as the barometric pressure changes.
This information turned out to be one of the most important factors
leading to successful fly fishing on the flats
...............especially for permit.
Gordy