4. Season of Retreating Monsoon

The south-west monsoon begins to retreat from northern India by the third week of September with the southward migration of the sun. By the end of September, the south-west monsoon retreats from the Punjab plains and adjacent regions. However, unlike the sudden burst of monsoon, the retreat is steady and gradual (Fig. 4.19). By mid-October, the southerly branch of the jet stream returns to its winter position south of the Himalayas.

The temperature during the season of retreating monsoon is uniformally high being about 25°C in the beginning of October in Northern India. The day temperature is generally high, but nights become pleasant with the mean going down to 20°C or even lower. The temperature begins to decline in November and by December cold weather sets in with about 1.5°C average temperature in the north and north-west parts of Indian plains, about 20°C in the central parts of India, and about 2.5°C along the coasts.

Fig. 4.19 Mean October Temperature

With the advent of October, the low pressure area over the north western parts of India is dissipated and its place is taken by the low pressure cell located over the northern parts of Bengal. By the beginning of December it moves further southwards and by month end, it merges with the equatorial low. The winds are westerly in the north-western parts of the country and in the Ganga Plain, north-easterly in the Peninsular region and north-westerly in the east coast.