How do I read a sea temperature chart for fishing?

What the chart is showing you

Every color on a sea temperature chart is a temperature, and the legend tells you which. The first picture is the map as the report draws it. The second answers a different question: not how warm the water is, but how warm it is for the date.

Sea surface temperature

1234567

1. 1 The day. Drawn from that morning’s report and the layers stored for that day.
2. 2 Legend and layer time. Blue is 84.0 F, red is 87.5 F. The stamp under the bar says when the satellite saw the water: Thursday, October 1, 5 AM.
3. 3 Cool water. Florida Bay and a cooler band along the outside of the Keys.
4. 4 The step. Moving offshore the colors climb from green through yellow to orange. This is the climb the report measured.
5. 5 The top of the climb. Orange water to the south of the reef: the warm side of the step.
6. 6 Spot 1. The report’s top pick sits where the cool water has started to climb.
7. 7 Layer picker. Switch the water underneath. The SST Anomaly layer is in this list.

Sea surface temperature anomaly

1234

1. 1 Legend and layer time. White is normal for the date, red is warmer than normal, blue is cooler. This one runs from -2.5 to +2.5 F, as of Wednesday, September 30, 5 AM.
2. 2 Near-normal water. The pale band hugging the Keys and Florida Bay.
3. 3 Warmer than normal. Red offshore: most of the frame is above normal for the date.
4. 4 Spot 1. The pale water gives way to red a short way offshore.

How to read it on October 2

Four reads, in the order a captain would make them.

1. READ 1

   Find the cool and the warm

   Cool water filled Florida Bay, and a cooler band hugged the outside of the Keys. Moving offshore from Alligator Reef the water warmed steadily toward a warm tongue the report’s imagery read centered roughly 20 to 25 miles ESE.

2. READ 2

   Size the step

   The report read the climb as 2.4 degrees across roughly 15 NM: a soft step rather than a knife edge. A knife edge crams the color change into a short distance, so the colors meet in a line. A soft step spreads it over miles, so they blend.

3. READ 3

   Find where it tightens

   The step runs northeast to southwest, parallel to the reef line, and the imagery read put its tightest part 5 to 10 miles outside the reef. That is the stretch of the step worth a pass first.

4. READ 4

   Do not fish the even sheet

   The southeast corner of the chart cooled slightly again. A broad sheet of warm water with no step in it is just warm. The edge of the tongue is the feature, not the middle of it.

What to do with it

A temperature step on its own is a maybe. The report’s ranked spots lean on it as one edge among several: on October 2, spot 1 had the temperature break, a chlorophyll front and the report’s eddy factor from its sea level gradient read overlapping, which is why it ranked first. That factor comes from a sea height step, not a closed eddy in the temperature picture. The convergence map page shows how that stacking works.

To check a spot against this chart, about a minute:

1. Open the report’s map and switch it to Sea Surface Temperature.
2. Find the spot’s pin. Is it on a color change, or in the middle of one color?
3. Switch to the anomaly layer. Is the water there near normal, or well off it?
4. Read the layer’s time under the legend, then go back to the report’s wind and seas before you decide to run.

What the chart cannot tell you

• It is a day or two old. The layer on this map is stamped Thursday, October 1, 5 AM, on a Friday report, and the report’s data note counts the age of every layer it used. An edge moves; check the stamp.
• It is the surface. A satellite sees the skin of the water, not what is a hundred feet down.
• Clouds blur it. A satellite cannot see through cloud, so the product fills the gaps and edges can read softer than they are. When a day’s preferred source is unavailable the report falls back to a backup and says so in its data note.
• It is not a fishability score. Warm water with a Small Craft Advisory on top of it is still a rough day. The best water tells you where. The forecast tells you whether.

What this looked like on the water

That morning’s report told anglers to troll the warming step where the mid-80s climb toward the 87.0 tongue, working it northeast to southwest, and put its first look 4 to 10 miles off Alligator Reef, where the warming step and the color line overlap. The same morning carried a Small Craft Advisory until 8 PM, so the plan was written around the weather as much as the water.

FishIntel is for information only. It is not for navigation or safety-of-life decisions.