What would it take for an island to sink and rise yearly and naturally

So I'm writing a book and need help to better explain this island that sinks, more on that in a moment as I give you the basic build of the planet...

First, its a world on a very tilted angle. the south continent like Antarctica would be is mostly a summer paradise with short 6 hour nights.

The world is mostly similar to earth, 24 hour days, but with 15 month years. The north part of the planet is usually cold and always dark, say except for 2-3 months a year the tilt and wobble allows for daylight to hit to the top of the planet giving it roughly 3-5 hours of daylight per day for those 2-3 months.

So the idea is most continents at the equator of the planet, pretty much all of them, experience the regular cycles of earth, seasons ext ext.

But one continent is divided into two islands, the north and the south, the north sister island being a third of the size of the southern. And every year for at the very least 30-60 days. The sea level falls low enough that the part of the island that is now underwater comes above land & connects both halves. And sink low enough, not for mountains, but at least city's or towns to submerge.

Size of the part that sinks would be about the size of mexico if not double that. And it would make up about 25% of the total island when both ends are connected.

While the rest of the world does not sink or rise that dramatically. only this one island or continent mainly.

I was wondering if there is anyway this could be possible so i'm open to most ideas. My best guess was the ice would melt and freeze in such large proportions at the north it would lower and raise the sea level, but this would effect the world as a whole I would imagine... ... ...

Bonus question would also be, would the south be a tropical paradise? or would it burn into oblivion? I'm sorry for all the information, I just figured it would help gear everyone to an answer that would help make such a fantasy world sound a bit more real but still be this insane world. And I'm just unsure if there is any solution to this at all...

----EDIT---- So far I like the moon idea and even having two of them, It does seem really difficult as many suggest but I am considering putting the two on a horse shoe orbit if that would at all help this situation.

posted about 6 years ago

WolvesEyes‭

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