Pre-monsoon showers bring short-term relief from heat: A look at India's southwest monsoon types, expected time of arrival

As rains greeted Mumbai on Monday, several rejoiced stating that the monsoon season is finally here to give the city a break from the sweltering heat. However, unlike what several reports claimed, these were actually pre-monsoon showers. What’s the difference? Well, the Indian Meteorological Department (IMD) has divided the Indian monsoon season into three parts. The pre-monsoon season occurs from March to May. It is also called mango showers or summer rain. There are characterised by squally winds, ie, they come with sudden, sharp winds that last for a long time and occur during the rain, and thunderstorms or heavy snows. They also bring with them heat and humidity in the day and night. The rains are sharp and intense but go away, after one downpour. The rains are usually patchy. The showers that greeted Mumbai on Monday are an example of that. [caption id=“attachment_6794591” align=“alignnone” width=“1013”] The arrival of Southwest Monsoon in India (2019). Image credit: IMD[/caption] From June ­to September is the season for the Southwest Monsoon. The dry north-westerly winds are replaced by warms and moist south-westerly rains. This season brings about 70 percent of the country’s rains. We experience stratiform clouds or layer clouds that are formed in stable and horizontal layers. June is the onset of the monsoon with July to August being the most active months. September is the time they wave goodbye. According to IMD predicitons, Southwest rains have set in the Lakshadweep island by 25 May and in Kerala, on 8 June 2019, the western and northwestern parts of India, ie, Gujarat, Rajasthan, Punjab and Haryana will expect their monsoons showers by 1-15 July. In the eastern states of India like Odisha, Andhra Pradesh and West Bengal, the Southwest Monsoon will arrive by 10 June while the northeastern states like Assam and Meghalaya have already received their first showers. [caption id=“attachment_6794611” align=“alignnone” width=“1280”] Representational image. Image credit: Reuters[/caption] The post-monsoon season lasts from October ­to December and it is the time the monsoon usually retreats from India. It takes place due to the low-pressure area over the northern parts of India due to temperature changes after the rains. By mid-December, the centre of the low pressure is not in the peninsula. [caption id=“attachment_6794561” align=“alignnone” width=“860”] A map showing the post-monsoon showers in India. Image courtesy: IMD Pune[/caption] During this period, the temperature rises and the weather can be a little unbearable due to the humidity in the air. This is also known as October heat. Winter monsoons do not cause rainfall as they are moving from the land to the sea and hence have less humidity. But there are exceptions as well because these months cause the most rains in Tamil Nadu. Arunachal Pradesh and Assam also receive rainfalls during winter monsoons.