There’s an algorithm you can use to calculate future tides but it’s complex and I wasn’t sure it would even run fast enough on the watch. I gave up after a few hours and ended up generating an array of high/low tide levels and times for the next few years. NOAA has all the tide data you could possibly want, and an api to grab it.
https://tidesandcurrents.noaa.gov/tide_predictions.html
https://api.tidesandcurrents.noaa.gov/api/prod/