More information about tides
There are actually two tidal cycles: a twice-daily cycle and a once-daily cycle. On a tide when the two cycles help each other, high tides will be higher and low tides lower. On the next tide, when they conflict, the tidal range will be smaller. The relative strength of these two cycles varies from week to week, and also varies from one place to another. In the United Stares, along the Atlantic Coast the two daily tides have a similar range, but on the northern Pacific Coast there tends to be a large difference between the two daily tides. Farther south and in the Gulf of Mexico, the difference is so great there often appears to be just one high tide and one low tide per day. Abnormal atmospheric pressure can temporarily affect the time and height of tides. A difference of one inch in barometric pressure will cause about one foot difference in sea level. Strong on-shore winds will also cause a temporary increase in sea level. Both of these effects will change the times of low and high tides as well. Tides in the lower portions of rivers will be affected by the changing volume of the river flow.