After this week, I decided to add a new feature to the forecast tables, water level. I normally include low and high tide data as that is definitely important, but I don’t think it necessarily captures the whole picture.

First, What is Tide Data?

Tide data is almost always given in MLLW (mean lower low water) format. This format relates the water level to historic data of the mean lowest daily tidal value over a lookback period. In practice, this means that if you take every low tide value over a 24 hour period, pick the lowest of the two, record it in a ledger, then take the average of those values, you have your zero. From there, you get a new value, difference the reference from the new value, and this gives you your tide prediction. This is what you will see on virtually every surf forecasting website, app, etc. as well as what I use in my tide tables and in the tide graphs of my instagram posts.

Now, What is “Water Level”

After this week, I felt it was valuable to add another data point to my surf forecast tables. This is “water level” which is relative to the mean sea level over time. The “zero” in this case is closer to mid-tide rather than low tide. I have come to prefer this value as I think it gives a better estimation of what you’ll see at the beach when you go surf.