- Tides are based on the lunar day, which is 24 hours and 50 minutes. That's why you can't go to the San Francisco Bay the same time every day to observe a high tide or low tide -- you have to plan ahead.
- The moon has the largest affect on the tides, but the sun does play a role (especially at the vernal and autumnal equinoxes and winter and summer solstices).
- Neap tides coincide with the 1st Quarter and Last Quarter phases of the lunar cycle.
- Spring tides coincide with the New Moon and Full Moon phases.
- Spring tides not only produce higher high tides, but also lower low tides, creating a greater tidal range.
- The Bay has semi diurnal tides, with two unequal high tides (HH and H) and two unequal low tides (LL and L) each lunar day.
The NOAA publishes its tidal predictions based on the very predictable lunar and solar cycles -- meteorological factors (rain, snow, drought) are not used in the predictions because they cannot be predicted. The meteorological effects on the tides are measured by NOAA and are represented in the preliminary and verified water level data -- they just are not included in predictions.
The water level for the high tide on the morning of April 13, 2011 was predicted to reach 5.11' at 8:06 a.m. and hold steady through 8:18 a.m., dropping to only 5.10 at 8:24 a.m. In the chart, the Accoustc data shows that the actual water level reached 5.16' at 8:06 a.m. and held mostly level, as 8.15' is only 1/8 of an inch lower than 5.16, but did peak at 5.17' at 8:30 a.m.
Station Date Time Pred 6 Acoustc Backup DCP#: 1 1 2 Units: Feet Feet Feet Data%: MLLW Local 100.00 100.00 100.00 Maximum: 5.21 5.17 5.18 Minimum: 0.13 0.23 0.24 ------- -------- ----- ------- ------- -------
9414863 20110413 07:54 5.09 5.08 5.09
9414863 20110413 08:00 5.10 5.12 5.13
9414863 20110413 08:06 5.11 5.16 5.16
9414863 20110413 08:12 5.11 5.15 5.16
9414863 20110413 08:18 5.11 5.15 5.16
9414863 20110413 08:24 5.10 5.16 5.17
9414863 20110413 08:30 5.09 5.17 5.18
9414863 20110413 08:36 5.08 5.15 5.16
9414863 20110413 08:42 5.06 5.12 5.14
9414863 20110413 08:48 5.03 5.11 5.12
Here are the water levels critical to this case:
5.45' MHW (average of all H and HH tides)5.88' water level from HH tide on morning of April 13, 20036.05' MHHW (average of only the HH tides)6.39' water level for People's 100
As you can see, 5.11' (predicted) and 5.17' (Accoustc) are not anywhere near the 6.39' of People's 100; they aren't even close to the 6.05' MHHW; and even fall short of the 5.45' MHW. So just how common is it to have high tides this low? The answer is in this monthly plot for April 2011. I included the last several days of March to get a more complete lunar cycle, as taken from calendar-365.com, which has a lot of other very interesting information, too.
You can see from the plot that only 5 HH tides of the whole period equal or exceed 6.39', and they are boxed in red. So the real question is, Is it more likely for high tides to be at or below 5.11' or at or above 6.39' in the month of April?
During the month of April 2011, there are 58 high tides. We must include all high tides to determine the frequency of the 6.39' tide of People's 100 because Distaso did so in this broad statement in his Closing Argument: Remember that area where he came ashore is a tidal flat, so at high tide it's covered with water all the way.
Only 20/58 or 34% of high tides in April 2011 are predicted to reach or exceed 5.45' MHW
Only 7/58 or 12% of high tides in April 2011 are predicted to reach or exceed 6.05' MHHW
Only 5/58 or 9% of high tides in April 2011 are predicted to reach or exceed 6.39' People's 100
26/58 or 45% of high tides in April 2011 are predicted to be at or below the 5.11' tide predicted for April 13, 2011
That plainly means that more than 5 times as many high tides in April 2011 are at or lower than 5.11' than at or above 6.39'. That makes a 5.11' or lower tide 5 times more common than a 6.39' or higher tide. The tide on April 1, 2011 actually peaked at 5.17', and the photos I posted yesterday prove that the site is definitely not under water at this water level.
Lest you think April 2011 would be much different from April 2003, here is the verified water level vs. predicted water level plot for April 2003. The red + indicates the verified water level, and the blue line the predicted. As you can see, only 4 of the high tides were predicted to reach 6.39' or higher (a 5th one made it with the help of local meteorological factors); and only 6 to reach 6.05' or higher. Moreover, the storm surge that the State talked about so much didn't even raise the water level to the 6.05'.
And here is the verified water level vs. Predicted plot for April 2004, showing the same pattern.
People's 100 was taken on January 10, 2004. The month of January does traditionally produce higher tides than the month of April. That's because January follows the winter solstice when the sun has the greatest effect on the tides, and April follows the vernal equinox, when the sun has the least effect. Following are plots for January 2003, January 2004, and January 2011.
The Conner Recovery site simply is not "under water" at every high tide, and People's 100 does not represent what the site looked like on April 13, 2003.