In what atmospheric conditions a Tropical storm already formed in Northern Hemisphere crosses the Equator and?

Question

moves South? Is any one keep account of a recent ones (within this decade)

Answer 1

As the coriolis force is weak near the equator,the tropical storm will get weakened if it moves near the equator and in any case can not cross the equator as it will meet its end once it crosses the equator.

Answer 2

I don't know that there's any record of a tropical storm crossing the equator.  It is very rare for a tropical storm to even move toward the equator.  They don't form very close to the equator because they need the Coriolis Force to form, and that goes to zero at the equator.

That being said, I don't believe it is impossible.  While the Coriolis Force vanishes at the equator, the storm could remain in cyclostrophic balance--that is a balance between the rotational motion of the winds and the pressure gradient force.  If that were to happen, the storm would continue to rotate the same way after it crosses the equator.

While this has never happened with tropical storms, it has almost certainly happened with tornadoes/waterspouts, although they are so localized and short-lived there would probably not be a record of it.