No. IV-18.4 - (IMD), Pune

9
still less common. The heaviest falls are generally along coastal Tamil Nadu
and Coastal Andhra Pradesh where rainfall amounts as high as 40 cm to 50 cm have
been recorded. Such high falls are usually in association with the passage of
cyclonic storms and depressions across the area. Record heavy falls at the
observatories are given in the departmental publication - India Weather Review,
Oct.-Dec. 1963.
4.2 Heavy falls in south Peninsula occur mainly in the months of October
and November. In December, they are very rare except in the southern parts of
coastal Tamil Nadu, though even here the frequency is small compared to
November.
4.3 In Tamil Nadu itself, the south coastal districts get the maximum frequency
of heavy rains; compared to the coastal areas, the interior districts
get heavy rains on a considerably less number of occasions although in the
hill districts, the frequency is larger particularly in November. Even in
south Tamil Nadu, the highest frequency of heavy rain is only about 2 days in
November. In contrast, during the southwest monsoon season, along the west
coast, Mangalore gets about 3—4 days of heavy rain in a month at the height of
the monsoon season there.
4.4 During the northeast monsoon season, rainfall spells extend upto 3-4
days; spells exceeding 4 days are very much smaller in number (about 20%),
though spells even longer than 10 days have occurred. There are sometimes long
no
spells with little or heavy rain, which on some rare occasions have been even
longer than in the non-monsoon months.
5. Diurnal Variation of Rainfall
5.1 During the post-monsoon season except in the beginning, rainfall is
generally more during night and early morning (1730 to 0830 IST) than during
the rest of the period. In the eastern portions of south Peninsula (i.e. in
Tamil Nadu),/rainfall is mostly between 2100 and 0300 IST and in the western por-