This is an old post from an old blog of mine, but I figured it might still be applicable.
Oh and I got a snazzy new watch that tells the moon phase and tide phase and thought that I would post the formula and answer to the San Diego Lunitidal hours interval:
The formula as you will find on the noaa website is in this F.A.Q.
Local Interval = GI – (0.069 * L)
- Where L is the longitude for the location in degrees. West longitudes are positive; East longitudes are negative.
Example: 122 degrees 23.7 minutes West would be 122.395 degrees. (23.7 / 60 = 0.395)
- Longitude for a station is available from the Accepted Datums page by using the link provided for further station information.
- Where GI is the Greenwich Interval. To calculate the High Tide Local Interval, use the Greenwich Mean High Water Interval in Hours from the Accepted Datums page. To calculate the Low Tide Local Interval, use the Greenwich Mean Low Water Interval in Hours.
- Some products will require the Local Interval to be a positive number. You can convert a negative interval to a positive by adding 12.42 to the result.
For example, if your interval calculated to be -4.11; you could also use 8.31 (-4.11 + 12.42 = 8.31)
While this looks all dandy, here is how to get the answer (for La Jolla which is closest to me, and where I will be diving)
La Jolla HWI
Check the HWI (Greenwich High Water Interval) which for La Jolla is 5.01 so the formula looks like
L: -117.257 (close enough)
0.069 * -117.257 = 8.09
5.01 – 8.09 = -3.08
-3.08 + 12.42 = 9:34 (Local Time Interval for La Jolla).
Share and Enjoy!