Each year the National Oceanographic and Atmospheric Administration (NOAA) publishes charts of tidal predictions for the year for many coastal locations around the country. Although the the country experiences the same phase of the moon at the same time, differences in the way the tidal wave interacts with the specific geography of ocean basins causes the tidal expression to vary considerably from place to place. Tidal charts can be purchased in paper form at any store that sells fishing or marine supplies. Tidal predictions can also be accessed online through the WWW Tide and Current Predictor or through NOAA's Oceanographic Products and Services Division (OPSD).
The published tables for San Francisco Bay are for tidal variations at the Golden Gate. Because the tidal wave must propagate into San Francisco Bay through a narrow inlet, the times of the high and low tides are increasingly delayed with distance from the Golden Gate.
Go to NOAA's OPSD and click on California to see a list of locations within the state. Clicking on San Francisco Bay (Golden Gate to San Mateo Bridge) will bring up a list of tidal differences for locations within San Francisco Bay. The first two columns are the time differences for the high and low tide between Bay locations and the Golden Gate. Times are in hours and minutes (for example, +1.20 means the time is 1 hour, 20 minutes later than at the Golden Gate; -0.45 means the time is 45 minutes earlier than at the Golden Gate).
The third and fourth columns are the elevation differences for the high and low tides between Bay locations and the Golden Gate. Elevations are shown in feet higher (+) or lower (-). For example, +1.2 means 1.2 feet higher than at the Golden Gate. Elevations shown with * are ratios; for example, *1.45 means the level is 1.45 times the level at the Golden Gate.
The map below shows the different parts of San Francisco Bay. On the OPSD web site, examine the tidal differences for locations within San Francisco Bay (Central and South) and within San Pablo and Suisun Bay.
1. What generalizations can you make about the time differences of the high and low tides as one moves further into the Bay (away from the Golden Gate)?
2. What generalizations can you make about the elevation differences of the high and low tides as one moves further into the Bay (away from the Golden Gate)?
Scroll up the California tidal differences list to the Outer Coast locations.
3. How do the time differences along the outer coast (for example, Ocean Beach or Santa Cruz) compare to the time differences within the Bay?
Click on any of the highlighted San Franciscos (last column) to get the list of daily tidal predictions for the Golden Gate. Look at the data for the current month.
4. Plan an activity for which you would need to know the tidal level (for example, fishing, boating, looking at shore birds). Choose a location and a date and calculate the time and elevation of the high or low tide at that time and place.