Weather and climate of Southern India is dominated by the monsoon. This region has a unique peculiarity that both Southwest and Southeast Monsoon hit the region and no month of the year is actually dry.
The following is a brief overview of the climate to be expected during the above mentioned monsoons.
The South West Monsoon Climate
This Monsoon arrives in South and South west of India in early June and continues to affect till the middle of October and sometimes up to November. The typical weather is heavy rain and high air relative humidity. The temperatures remain moderate. The highs rarely cross 85 F and lows are around 75 F. The air is cool and pleasant during rains but otherwise becomes sultry due to high relative humidity.
The rainfall can be as much as 80 inches or more especially on Kerala and Goa Coast. A little distance away from the Western Ghats, the rain reduces sharply because it cannot cross the high mountains of the Ghats.
The months of October November and December are relatively dry but then this area gets some rain from the Southeast monsoon from December onwards to February.
The South East Monsoon Climate
The typical area that falls under this category is the south and southeast of India including almost whole of Tamil Nadu state but especially the area around Chennai and Pondicherry. Bengaluru in Karnataka also gets appreciable amount of rain from this system. Here the rainy season is the Southeast monsoon instead of Southwest monsoon. In this region, the monsoon starts in November and continues up to February with full furry and force. The general features of weather are similar to those of the Southwest monsoon. Thick dark clouds, cool breeze and copious rain is the norm. The temperatures are around 80 F and the relative humidity is around 80 percent. The areas with located at a comfortable elevation like Bengaluru and the Nilgiri Hills enjoy moderate to cool climate.
The characteristic features of this part of India where Chennai is located is that although in the North and Central India, it is the height of winter season with nighttime temperatures nowhere greater than 55 F, in Chennai it seldom falls below 70 -thanks to the high relative humidity and the accompanied heavy rain.
From the above discussion it becomes crystal clear that no month in South India is dry as opposed to the Northern Part where a long and definite dry season exists.