What Is a Monsoon

A monsoon is a large-scale seasonal reversal of the prevailing winds, which brings a marked wet season and dry season to a region. It is not a single storm but a wind system that lasts for months. The word comes from the Arabic 'mawsim', meaning season. The most famous example is the South Asian summer monsoon, when winds turn to blow from the ocean onto the land and unload heavy rain across India and neighbouring countries. Sources: NOAA, Britannica.

Monsoons are driven by the difference in how fast land and ocean heat up and cool down. In summer the land heats much faster than the sea, creating an area of low pressure over the continent that draws in cool, moisture-laden air from the ocean, this air rises, cools and produces heavy rain. In winter the land cools faster than the sea, the flow reverses, and dry air blows from the land out to sea, giving the dry season. Sources: NOAA, Britannica.

It depends on the region. The South Asian summer monsoon runs roughly from June to September, typically arriving over Kerala in southern India around the start of June and withdrawing by late September or October. The North American monsoon peaks from about July to September, and the Australian monsoon falls in the southern-hemisphere summer, around December to March. Sources: India Meteorological Department, NOAA.

Monsoon systems occur in several parts of the world, not just India. The largest is the Asian monsoon (South Asia and East Asia). There are also the West African monsoon, the Australian and Indonesian monsoon, and the North American monsoon that affects the southwestern United States and northwestern Mexico. All share the same basic mechanism: a seasonal reversal of winds between land and sea. Sources: NOAA, Britannica.

No. A hurricane or typhoon is a single, intense tropical cyclone that lasts days. A monsoon is a seasonal wind pattern that governs the weather of an entire region for months at a time. Tropical cyclones can occur during a monsoon season and add to the rainfall, but the monsoon itself is a climate feature, not one storm. Sources: NOAA, Britannica.

Yes. The North American monsoon, sometimes called the Southwest monsoon, brings a surge of moisture and afternoon thunderstorms to Arizona, New Mexico and parts of northwestern Mexico from roughly June or July into September. It is much smaller than the Asian monsoon but is a genuine monsoon by the same definition, a seasonal shift in wind and moisture. Sources: NOAA, National Weather Service.

The wet (summer) monsoon is when winds blow from the ocean onto the warm land, carrying moisture that falls as heavy, sustained rain. The dry (winter) monsoon is the reverse: as the land cools, winds blow from the land out to the ocean, bringing clear, dry conditions. The two phases together, driven by the same land-sea temperature contrast, are what make a climate a monsoon climate. Sources: Britannica, NOAA.

For billions of people the monsoon is the main source of fresh water. In India, for example, the summer monsoon delivers most of the country's annual rainfall and underpins agriculture, drinking water, hydropower and the wider economy. A strong, well-timed monsoon supports good harvests; a weak or late one can cause drought and food shortages, which is why its arrival is watched so closely. Sources: India Meteorological Department, Britannica.

Yes. While the monsoon is vital for water, its heavy and concentrated rainfall can also cause serious flooding, flash floods and landslides, damaging homes, crops and infrastructure and forcing people to evacuate. The same season that fills reservoirs can, in a bad year, bring destructive floods, so monsoon forecasting and flood management are a major focus for affected countries. Sources: NOAA, India Meteorological Department.