Free SST Charts: Where to Find Them, and When They're Enough

Short version: every SST chart service, including ours, starts from free government satellite data. You can look at that data yourself for nothing. A paid service saves you the time it takes to find it, clean it up and read it on the boat. Here are the best free sources, how to use them, and an honest take on when they're enough.

Where satellite SST comes from

Sea surface temperature comes from sensors on polar orbiting satellites (like VIIRS on the NOAA and NASA JPSS satellites) and geostationary satellites (the GOES series over the Americas). NOAA, NASA and partner agencies process those passes and publish them free. The paid services download the same passes, then blend, clean and color them into fishing charts.

So the raw data isn't the secret. What you pay for is everything that happens after.

The best free sources

• NOAA CoastWatch: NOAA's home for satellite ocean data, including SST and chlorophyll. Great data, built more for scientists than anglers, so expect some digging.
• CoastWatch West Coast ERDDAP: a data server where you can pull SST and chlorophyll for a box you choose and make a quick map. Powerful once you learn it, and a bit of a learning curve.
• NASA Worldview: the easiest free place to look. Turn on a sea surface temperature layer and true color, pick a date, and scroll around. It's good for a quick look at the big picture.
• NOAA GOES imagery: near live geostationary images, handy for checking cloud cover before you plan around a satellite pass.
• Regional ocean observing sites: on the West Coast, CeNCOOS (central and northern California) and SCCOOS (Southern California); on the East Coast, Rutgers RUCOOL is a long time favorite for Mid-Atlantic SST.
• NDBC buoys: real in water temperatures, wind and waves. We put them on one page per area at water temps, free.
• IOOS HF radar: free surface current maps for most US coasts, useful for seeing which way an edge is drifting.

How to read free SST without getting fooled

Free single pass images are honest, but raw. A few things trip people up:

• Clouds look like missing water. A single pass is often half cloud. Blank or speckled patches are clouds, not cold water. See why your region looks cloudy.
• One pass is one moment. An afternoon pass on a calm day can read warmer at the skin than the water a meter down. Check a buoy before you trust a hot spot. More in ground-truthing SST with buoys.
• Color scales differ. Two sites can color the same water differently. Look at the numbers, not just the colors.
• Look at a few days. A break that shows up on several passes is real. One that shows up once may be noise. Our post on composite vs single pass goes deeper.

When free is enough

Free sources are plenty if you fish one area, you're comfortable at a computer, you plan the night before, and you have time to flip through a few passes and a buoy or two. Lots of good anglers do exactly that.

When a paid chart is worth it

A paid chart earns its money when you want the work done for you:

• Clouds filled in. Blending days of passes so the break reads as one clean line instead of a patchwork.
• Fishing tools on top. Depth contours, waypoints, distance and bearing, your units and GPS format.
• One place, on your phone. SST, chlorophyll and true color lined up on the same map, quick to check at the dock.
• More than one area. If you trailer the boat or travel, having every region in one place saves a lot of hunting.

That's what we built ReelTemps to do. If you want to see how it compares to FishTrack, RipCharts and Hilton's, including what they do that we don't, see our comparison page.

The honest bottom line

Start with the free stuff. If you find yourself spending an hour every trip stitching passes together, a paid chart pays for itself in fuel and time. If you don't, keep using the free sources, and check the buoys before you go.

Not for navigation.