The climate of South India is hot and humid throughout the year with heavy rainfall in the monsoon season.
The most characteristic feature of the climate of South India is the uniformity of its temperature. At Cochin, for instance the thermometer rarely rises above 90 F in summer or fall below 80 F in winter. The night temperatures , throughout the year, hover around 70 F. The air is always charged with a high water vapor content and it is rare to record a humidity figure of less than 80 percent. The high temperature combined with excessive humidity makes the weather conditions oppressive and unwelcoming for the foreigners especially Europeans.
The story is different , however at the hill stations of Nilgiri Hills and hill stations like Oooty have an ideal temperature. Located over 8000 ft above sea level Oooty has cool winters and mild summers. The average winter temperature is 60 F and the summer mean does not exceed 75 F . No doubt then it was one of the favorite hill stations of the British during the Raj.
As regards the rainfall, it is heavy almost everywhere in South India –especially on the West coast. The stations of Cochin and Mangalore are notorious for their exceptionally high rainfall and cloud obstructed skies. The rainfall is heavier on the hills than on the plain stations. The period from June to September should be avoided while visiting South India for this is the season of heavy monsoon rains.
In short the climate of South India is tropical with exceptionally heavy rains during the monsoons.