You need to specify in the question what you are talking about.
Floods usually occur in florida. {I think}
they usually occur in summer
They usually occur in desert or places on the equator.
The chance that a given event will occur, usually expressed between the number 0 (will not occur) and 1 (will occur) is called probability.
Volcanoes occur on tectonic plate boundaries
Rotations are usually assumed to occur counterclockwise unless otherwise specified.
Droughts in America usually occur in the summer and hot seasons
it usually occur from september to november.
it usually occur from september to november.
in the winter
They occur during REM sleep, usually in the second half of the night
They usually occur in places where two plates meet- faults.