The heavier rainfall in the country is caused by the cyclones which come from the two tropical cyclone zones: namely, the North Atlantic Ocean Zone and the Northeast Pacific Ocean Zone. Tropical storms and hurricanes from the North Atlantic Ocean zone annually rose 8.3 times. Tropical cyclones that hit the country one or two times a year occur from May to mid-December, and the occurrence frequency is at its highest level in mid-September.
Tracks of the tropical cyclones from the northeastern Pacific Ocean.

(Flood Control Project No. 69, 1985)