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July 19-20, 2014 - My "Cardinal" Rule

Bob Diaz | SpearBlog 2014 | July 21, 2014 | Print
visibility, clean, cardinal, rule, wind
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Wind Seas Viz Temp
5-10 WSW 1-2' 15' 88F

This past weekend the weather was still beautiful (beautifully HOT) as it has been for weeks now with mild winds and calm seas. But this week we were met with green, dirty water in almost every direction. In looking back at the weather, one thing had changed over the prior week that seems to support a theory I've been fostering for a while now about when and where we're able to find clean water depending on wind direction (hence the "cardinal"), the tide and surf temperature that I have dubbed my "Cardinal" rule. You see, we used to struggle with which direction to head in almost every time we would head out to the reef for spearfishing. All our bluewater fishing friends couldn't really understand why there was so much indifference (of course, why would they? All they do is head offshore for 20-40 miles) but for us it comes down to one simple fact... gas is expensive and making the wrong choice could have us burning daylight, fuel and patience, so I developed this slightly scientific approach that has held water (so to speak) since its inception.

antique style compass rose 512First off, two points:

  1. Some of what you will read here may be old hat to you, but in all the conversations I've had on this subject, no one else has ever claimed to have formulated the same theory so I decided to put my "stamp" on it here.
  2. My observations are limited to the areas that I frequent for spearfishing ranging from Long Key to Big Pine Key so your results may (and most likely will) vary.

It seems to me that the middle keys sit in a unique position because they stand to benefit (or suffer) from different potential clean water sources, the Atlantic Ocean to the East, the Florida Straits to the South and potentially (depending on how deep into the Keys you fish) the Gulf of Mexico to the West due to its general East/West orientation. Typically when we go spearfishing we have two options (if we don't count staying shallow), head East towards Long Key or head West towards Big Pine. The quandry is always how do we make the best educated guess so we're more likely to find clean water and hopefully fish? There have of course been cases where we experienced clean water in either direction but in those cases there really isn't any quandry, is there?

Our old approach would be to head in whichever direction it "appeared" the blue water was closer to the reef line and hope we were right. The downside to this approach was of course that we could possibly burn through 10-30 miles only to have to turn back around and try the other direction or give up on the reef completely and stay shallow.

What I've observed over the past couple of years is that the primary factor beyond the tide that seems to affect where we will find clean water is the direction of the wind. I realize that this in and of itself could go without stating (of course the winds affect the water, duh...), but I've been able to prove un-scientifically (at least to mysef and a few friends) that there are predictable patterns.

Wind from cardinal direction: Most likely clean water to:
East to Southeast Areas East of Sombrero light (Sombrero to Long Key)
South to Southwest Areas West of Sombrero light (Sombrero to Big Pine Key)
West Variable results but typically water shallower than 100' is dirty
North I have not made any observations for these conditions yet

There are two other points to consider as well:

  1. The tide of course plays a large factor as well. You're much more likely to find cleaner water on the incoming tide. So you should use your tide tables as well as the wind to get the best results.
  2. The last factor is surf temperature. I've noticed that sharp increases in surf temp (like one we had about 10 days ago when it shot from 79-85F), also lead to algae blooms that will affect your viz as much as any of the other conditions I mention here. 

I'm relatively certain that Sombero lighthouse doesn't have any special qualities that make it a true division between clean and dirty water or East and West, but it's pretty much the only landmark (or oceanmark) we have to mention for this purpose. Also keep in mind that the direction of the wind must be sustained in order to really have any effect on the conditions. So if you get a week of West winds and only a day or so of East, you're more likely to be experiencing the West wind conditions before any change takes effect. So make sure and monitor the wind for multiple days before your trip.

As with anything on my site, your mileage may vary, so take it with a grain of salt, break out your "Bill Nye the Science Guy" lab coat and make your own observations. The way I look at it is, anything that makes us pay attention, think and apply ourselves, makes us better ambassadors of spearfishing. Who knows, you might even learn something!