While not close to the theoretical maximum, the observed records are, nonetheless, stunning.

1 min - 31.2mm (1.23")

60 min - 305mm (12.0")

12 hr - 1.825 m (45.0")

24 hr - 2.467 m (97.1")

72 hr - 3.929 m (154.7")

96 hr - 4.869 m (191.7")

12 month - 26.47 m (1042")

source (http://wmo.asu.edu/#global)

Almost all of the records come from La Réunion ( http://en.wikipedia.org/wiki/R%C3%A9union ), which is an island straight east of Madagascar. If you're from the US, think of the Hawaiian islands but in the Indian Ocean. Significantly, the island has peaks that rise up to 3,070 meters (10,070 ft).

I am guessing large Indian Ocean cyclones get going and then just run slap into this vertical peak in the middle of the ocean. Then, rain. Rain for apparently days straight.