No. IV-18.4 - (IMD), Pune

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as far south as 10°N have caused normal monsoon in Coastal Andhra Pradesh.
While depressions and storms crossing Coastal Andhra Pradesh have caused
active to vigorous monsoon there, those recurving northeastwards even if they
come within 2 to 4 degrees of the coast, have often caused only normal
monsoon (Fig. 11.2).
11.2.2 Tamil Nadu
i)Tamil Nadu gets rainfall when storms and depressions or low pressure areas
affect the sub—division. In the case of storms and depressions, the monsoon
may be active to vigorous or normal depending upon the location of the
system and its movement during the preceeding 24 hrs. Low pressure areas
cause active to vigorous monsoon if they are well-marked; otherwise they
cause only normal monsoon. Tamil Nadu also gets rainfall when the seasonal
low in the west central Bay/ southwest Bay is well—marked or a trough line
runs east-west across the south Peninsula. On such occasions, monsoon
activity may be only normal.
ii)By far the most common systems causing rainfall in this sub-division are,
low pressure areas, well-marked seasonal low oyer Bay or an east-west oriented
trough line across the south Peninsula, in the surface and lower troposphere.
Next in frequency, are the depressions and storms; although less in
number than low pressure areas, storms and depressions cause heavy to very
heavy rains and contribute substantially to the season's total rainfall.
11.2.3 Rayalaseema
i)Rayalaseema gets most of its rain in association with the east-west trough
across the Peninsula in the lower troposphere becoming well-marked or with a
low pressure area/wave moving westwards across the Peninsula Over this subdivision,
the low pressure area may not be seen on the surface chart, but
only in the lower tropospheric wind field as a cyclonic circulation. All
these disturbances generally cause normal monsoon, except in October when
they may cause active monsoon also.