As the sun shifts northward towards the Tropic of Cancer after the Vernal Equinox, the whole India experiences an increase in temperature and marks the commencement of Pre-monsoon season.
Pre-monsoon is from March to May. The temperatures in the north India rise as the vertical rays of the Sun reach the Tropic of Cancer. April is considered the hottest month for the western and southern regions of the country. For most of North India, May is the hottest month. Temperatures of northwest India sometimes reaches 50 °C and higher.
Another striking feature of summer is the Loo (hot wind). strong, hot, and dry wind known as the loo blows in from the west during the daytime, with very high temperatures, in some cases up to around 45 °C. Isolated pockets of north and west Rajasthan sometimes reaches 50 °C also.
The atmospheric pressure is low all over the country due to high temperatures. Since the sun goes gradually towards the north (summer solstice), the Inter Tropical Convergence Zone (ITCZ) begins to move towards the north.
The general direction of winds is from the north-west and west in north-western India. In the months of May and June, the high temperature in north-western India builds a steep pressure gradient leading to strong winds. These strong dust storms result from the convective phenomenon and their intensity increases in the afternoon. These are locally known as Andhis, which are short-lived thunderstorms, which move like a solid wall of sand and dust. These weather activities bring little rainfall and give much-needed relief from the heat. Dust storms in the evening are very common during May in Punjab, Haryana, Eastern Rajasthan, and Uttar Pradesh.
Immense pre-monsoon squall-line thunderstorms, known locally as Kal Baisakhi or "Nor'westers", commonly associated with hailstorm and very strong winds, occurs in east India. During this time Odisha, West Bengal, Assam, Bihar, Chhattisgarh, Jharkhand, Bangladesh and North-Eastern states of India are affected by violent thunderstorms. They cause considerable damage to life and property.
In the south, thunderstorms occur in Kerala and adjoining parts of Karnataka and Tamil Nadu, particularly in the evenings and nights. These pre-monsoonal showers are called by various names:
Tea showers in Assam (they are good for tea, jute, and rice). Mango showers in Kerala and coastal areas of Karnataka as they help in the early ripening of mangoes. Cherry Blossoms/Coffee showers in Kerala and nearby areas (good for coffee plantations).
