I’m currently on phu quoc an island off the southern coast of Vietnam. I’ve been here two whole days and the sea level hasn’t changed in that time. To make it even stranger there is a sign on the beach saying that the sea is high and beach narrow between May-October and sea low and beach wide between November - April.
And indeed the sea is constantly “high” up against the high tide mark right now.
Is this possible? How? What kind if alternate dimension with mysterious extra moons have I slipped into?
To be clear this island is in the gulf of thailand, it’s open to the ocean it’s not in a lake or in an enclosed bay. I’ve been to several other locations around the gulf of thailand and they had normal high and low tides.
Here’s the tide table for nearby Duong Gong. It appears that over the last few days the tidal range has been only about 10 inches. Even a small amount of wave action would obscure that. In a week the tidal range will increase to about 3 feet, which will be more noticeable.
The amplitude of tides is greatly affected by the configuration of the coast. Here in Panama, the tidal range on the Caribbean coast, which is mostly open to the ocean, is only about 2 feet, while only 50 miles away in the Gulf of Panama on the Pacific the tidal range is as much as 18 feet.
The tidal signal is made up of various harmonic components adding constructively and destructively. Among the most familiar components are the 12.5 hour lunar, 12-hour solar, monthly and semi-annual.
For any one of these components, there can be regions where the amplitude is high and nodes where the amplitude is zero, thanks to interference patterns within a given body of water.
Greg Charles is correct, even if not a complete answer. The area changes as the sign states because of the very complicated movements of the earth, moon and their relationship to the sun.
It’s only amazing when you first learn about it, after that it can be frustrating because a lot of people simply will not believe it. I’m not kidding about that.
This image is a computer generated map, showing the points of no tide (called nodes, amphidromic points), but they are not fixed, nor are all of them shown. It’s a very very very complicated system, and it changes all the time.
What you are experiencing is an area where the complicated shifting amphidromes change yearly, which isn’t even the strangest thing about ocean tides.
I did not see those replies before posting, or I would have included them in my response. The map graphics are not actual looks at what occurs, there are multiple factors, so the nodes are not as simple as the images show, nor does water always behave as theory would say.
It’s very very very complicated, but the concept is sound. Ocean tides are nothing like what is taught showing two bulges following the moon around. The tides are giant circulating waves.
Do the tides have an affect in the middle of the ocean? Obvioulsy there’s no shoreline reference point so it may not matter, but does the surface level of the ocean actually increase or decrease with tides far from shore?
Because as the earth changes over the year, the amphidromic systems change to follow the changes. Not being familiar with that location, I can’t say with any authority what is happening, but it’s quite possible, and based on science. There are some really strange things that happen with ocean tides. In that area, obviously the yearly cycle matters a lot. Which means it’s a solar issue, the changes are due to the earth changing it’s tilt, and distance from the sun. This happens every year.
Yes, and if you look at the maps, you can see estimates of the change in the ocean surface height. At the nodes, there is no change. But everywhere else, it’s up and down.
But, and this is cool, the height at sea is always very little. It’s where these giant circulating waves pile up, due to land masses, that we observe large changes. In the deep ocean, the maximum tidal change is about a meter at most.
Is it possibly related to the monsoon season in southeast Asia, where rainstorms (high energy waves) occur in the summer months and the winter months are dry (low energy waves)?
