Water temperature in the Catalina Channel

There are 14 years of publicly available data on the surface water temperature in the Catalina (a.k.a. San Pedro) Channel – via¬†NOAA and CDIP. Unfortunately, that’s all it is – data. No summary statistics, no long-term charts – nothing particularly useful if you’re just looking for a simple, big-picture view of trends and cycles in sea temperature (perhaps to inform your upcoming swim across the channel).

So I decided to make one myself:

Catalina Channel water temperature, 1998-2012

NOAA buoys take readings every 30 minutes. Over 14 years, that works out to almost 239,000 observations. Don’t try this on an old computer! For a smoother line, I calculated a weekly average. Same data – just prettier.

If you really need more detail, I also made an interactive chart with daily-level resolution (5,044 observations). Keep in mind, Javascript is required to view the chart, and it probably won’t look good on mobile devices. If you’ve ever used Google Finance to view stock prices, the chart format will look familiar.

Summary Statistics by Day of Year

Sea temperature varies by season, but there are also year-to-year variations. In 2010, for example, the Catalina Channel was unusually cool (even in summer). In 2006 it was unusually warm. Perhaps you’ve wondered: What is the typical water temperature on a given day of the year? If your swim is scheduled for August 15, what is the average water temperature on August 15, averaged across all years?

To answer that question, I made this chart (click to enlarge):

Most Catalina swims take place in summer and early fall (not winter or spring), so here’s a zoomed version of the same data, for the swim season only:

So, water temps in the Catalina Channel tend to peak around August 1, and remain more or less steady through the first week of September. But even in early June and late October, the water is still “warm” by English Channel standards.

Note: It’s important to remember that surface water temps in Southern California tend to drop a few degrees as one approaches the coast, due to upwelling from the steeply sloping ocean bottom. My understanding is that this tends to happen about 3 miles from shore. So, if the buoy reading (6.5 miles offshore) is 63 degrees, the actual surface temp might actually be sub-60 during the last part of your swim.

13 thoughts on “Water temperature in the Catalina Channel”

  1. Thanks, Evan! This stuff is awesome. Are you also able to put together data from the swims that shows how much the temperature changes during a swim? Catalina conditions vary greatly from beginning to end. I also seem to remember there’s a flow model out there that illustrates the warm/cold pockets due to eddies and upwelling.

    1. Hi Ron! All I have is the data I scraped from the NOAA buoy, located about 6.5 miles SSW of San Pedro. I’m sure there are models that could describe/predict how surface temp changes as you move across the channel, but I’m not an oceanographer so I wouldn’t really know where to begin with that. My knowledge is limited to, basically, “It usually gets colder about 3 miles from the coast.” You might check out SCCOOS.

        1. Yes, I did. According to my observer’s report it started at 68F, stayed between 66-68 in the middle of the channel, and dropped to 62F at the end. I didn’t hit the colder water until the very end – perhaps the last mile or so – which is later that most people’s experience, I think.

          1. That’s a big change, down 2 degrees F is enough for chills, and I don’t recall you writing much about it in your report. (I have a shocking memory though). So how was it?

          2. Now that I think about it, you’re right – I didn’t write about it! It wasn’t really an important factor in my swim. When it dropped to 62 at the end the pain in my shoulders was such that I hardly noticed. I was pretty well acclimated anyway and I think I could’ve done the whole swim at 62 if necessary.

  2. All I know is that it is really cold right now (hanging out in the “minimum” zone), and I’m trying to work up the mental fortitude to break a 2 month ocean swimming hiatus.

    1. See here for the interactive chart, which has dual axes.

      Unfortunately the software I used for the static chart doesn’t allow dual axes, so I had to stick with F, ’cause Catalina is fahrenheit territory. Besides, Ollie, when you come swim Catalina your observer’s report will be in F, so better to learn now!

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