AUTUMN SEASON IN KERALA: OCTOBER-NOVEMBER
The month of September is moderately warm with less amount of rainfall. The Climate is moderate and pleasant. Days are bright and nights are cool. September is the last month of the South West monsoon, as it retreats from the sub-continent, sometimes with the accompaniment of convectional afternoon rains characterized by thunder and lightening. Tourist Season in Kerala starts from September.
Around October, after the winter equinoxes, the northern land mass of the Indian subcontinent begins to cool rapidly. With this, air pressure begins to build over northern India. The Indian Ocean and its surrounding atmosphere still hold its heat. This causes cold winds to sweep down from the Himalayas and Gangetic plain towards the vast expanse of the Indian Ocean, south of the Deccan peninsula. While travelling towards the Indian Ocean, the dry cold wind picks up some moisture from the Bay of Bengal and pours it over peninsular India and Sri Lanka. This is known as the Northeast Monsoon or Retreating Monsoon.
North East Monsoon hits Kerala during the months of October and November. These are called Thulavarsham - as it rains during the Malayalam month of Thulam. Days are warm and humid, but there is not much variation in night temperature.