Premonsoon

Premonsoon refers to the transitional period preceding the onset of the southwest monsoon over the Indian subcontinent and adjoining regions. It typically spans March to May, though the exact timing varies by location and year. The term can also be used for similar pre-monsoon periods in other tropical regions.

During the premonsoon, temperatures rise rapidly and the atmosphere often becomes more humid. Weather patterns are characterized by hot, dry or dust-laden conditions in arid and semi-arid areas, especially in northwestern India and Pakistan, followed by increased convective activity as moisture returns. Thunderstorms and squall lines become more common, bringing localized heavy rainfall, strong winds, and lightning. The phase is also associated with changing wind patterns and the slow northward migration of the Indian ITCZ (intertropical convergence zone), which helps set up the conditions for the monsoon.

Onset and regional variation: The premonsoon phase concludes with the development and establishment of the monsoon trough and a robust southwesterly monsoon flow. The arrival of the monsoon varies by region and year, typically occurring from late May to early June in many parts of the Indian subcontinent, though some areas see earlier or later onset. Southern parts of the Peninsula may experience a delayed or somewhat different timing compared to the northern plains.

Implications: The premonsoon influences agriculture, water management, and disaster preparedness, as heat waves, dust storms, and convective storms can affect crops, infrastructure, and health. Climate variability modes such as El Niño or La Niña can alter the timing and intensity of the premonsoon and subsequent monsoon season.