Thanks for the great question. Finding
information on all the storms that have been
active at one time in different oceans around the
world is not an easy feat, so hopefully this
information about the Atlantic and the Pacific
Ocean will help to answer your question.
In recent history there have been as many as 4
hurricanes in the Atlantic Ocean at one time, the
last time happening September 25-27, 1998 with
Hurricane Georges, Ivan, Jeanne, and Karl. A
climate modeler has guessed that there is
potential for a maximum of seven hurricanes in the
Atlantic at once, but this is very unlikely
because there just isn't enough space for them all
in the ocean.
This number is not counting cyclones
(hurricanes that form in the South Pacific and
Indian Oceans) or typhoons (hurricanes that
form in the Northwest Pacific Ocean, near Japan).
There have been as many as eight tropical
cyclones (storms that are slightly weaker than
hurricanes) active at once in the Pacific Ocean,
as recently as last July!
I hope that helps!