This article is from the Storms FAQ, by Chris Landsea firstname.lastname@example.org with numerous contributions by others.
While the Atlantic hurricane season is "officially" from 1 June to
30 November, the Atlantic basin shows a very peaked season with 78% of the
tropical storm days, 87% of the minor (Saffir-Simpson Scale categories
1 and 2 - see subject D1) hurricane days, and 96% of the intense (Saffir-
Simpson categories 3, 4 and 5) hurricane days occuring in August through
October (Landsea 1993). Peak activity is in early to mid September. Once
in a few years there may be a tropical cyclone occurring "out of season" -
primarily in May or December.
The Northeast Pacific basin has a broader peak with activity beginning
in late May or early June and going until late October or early November
with a peak in storminess in late August/early September.
The Northwest Pacific basin has tropical cyclones occurring all year
round regularly though there is a distinct minimum in February and the
first half of March. The main season goes from July to November with a
peak in late August/early September.
The North Indian basin has a double peak of activity in May and
November though tropical cyclones are seen from April to December. The
severe cyclonic storms (>33 m/s winds) occur almost exclusively from April
to June and late September to early December.
The Southwest Indian and Australian/Southeast Indian basins have very
similar annual cycles with tropical cyclones beginning in late October/
early November, reaching a double peak in activity - one in mid-January
and one in mid-February to early March, and then ending in May. The
Australian/Southeast Indian basin February lull in activity is a bit more
pronounced than the Southwest Indian basin's lull.
The Australian/Southwest Pacific basin begin with tropical cyclone
activity in late October/early November, reaches a single peak in late
February/early March, and then fades out in early May.
Globally, September is the most active month and May is the least
active month. (Neumann 1993)