The monsoon of South Asia is among several geographically distributed global monsoons. It affects the Indian subcontinent, where it is one of the oldest and most anticipated weather phenomena and an economically important pattern every year from June through September. Yet it is only partly understood and notoriously difficult to predict. Several theories have been proposed to explain the origin, process, strength, variability, distribution, and general vagaries of the monsoon, but understanding and predictability are still evolving.
The unique geographical features of the Indian subcontinent, along with associated atmospheric, oceanic, and geophysical factors, influence the behavior of the monsoon. Because of its effect on agriculture, on flora and fauna, and on the climates of nations such as Nepal, India, Bangladesh, Bhutan, Pakistan, and Sri Lanka — among other economic, social, and environmental effects — the monsoon is one of the most anticipated, tracked, and studied weather phenomena in the region. It has a significant effect on the overall well-being of residents and has even been dubbed the "real finance minister of India."
The word monsoon (derived from the Arabic "mausim," meaning "season"), although generally defined as a system of winds characterized by a seasonal reversal of direction, lacks a consistent, detailed definition. Some examples are:
The monsoon of the Indian subcontinent is primarily noted for the rain it bears and for the associated unpredictable weather. Consequently, some definitions incorporate rain.
Observed initially by sailors in the Arabian Sea traveling between Africa, India, and Southeast Asia, the monsoon can be categorized into two branches based on their spread over the subcontinent: