Spring and Neap Tides

On a climatology note, I noticed we are having high astronomical tides this week.  Our high tides are supposed to be 7.1 feet today (with normal being around 5.6 – 5.9).  This will definitely cause some shallow coastal flooding around high tide which is at 1:18PM in the Harbor.  Our low tides will be a bit lower than normal as well this week, which will be good for harvesting oysters.  This larger swing in tidal difference is caused by what are know as Spring Tides (I know, its fall, but bear with me).

Tides are caused mainly by the gravitational pull of the moon.  To greatly simplify things, if the moon is directly over your side of the earth, you are at high tide.  What a lot of people don’t realize is that the sun also exhibits a gravitational pull on the earth.  Spring tides are caused when the two gravitational forces are acting in the same line, essentially both working to “pull” the earth’s oceans to one side of the globe:

Spring Tides

Of course the opposite is true as well.  When the Earth is in the middle of the sun and the moon, the sun’s gravitational pull will cancel out a bit of the moon’s, which is called a neap tide.  Of course the sun is so far away, and its gravitational pull so weak, that it doesn’t cancel it out all together, and we do still have tides in this situation, just not as much of a difference between the high and the low.

Neap Tides

I suppose all of this information is fine and good, but it’s not going to help you if you are driving in downtown Charleston around the time of high tide early this afternoon.  For you, I can just say good luck, and I hope you have a truck.