Burst of the monsoon

Topic: Climate of India and the Monsoon · NCERT: Class 11, Ch 4 "Climate"

Meaning

The burst of the monsoon is the sudden arrival of heavy monsoon rain with violent thunder and lightning, instead of a slow, gradual increase in rain. It ends the hot, dry season almost overnight and cools the land sharply. It also tells farmers that the main rainy season has truly begun.

Explanation

How the burst happens (cause → process → result)

• The land heats and pulls in sea air.
• In April–May the sun shines straight down over the Tropic of Cancer (23.5°N).

• An intense low-pressure area forms over northwest India. The Indian Ocean stays cooler and keeps higher pressure.

• The trade winds cross the equator.

• This low pulls the southeast trade winds (steady winds of the Southern Hemisphere that blow towards the equator) across the equator between 40°E and 60°E.

• The Coriolis force (the bending of moving air caused by the Earth's spin) turns them to the right. They now blow from the southwest as the southwest monsoon.

• The winds load up with moisture.

• They pass over warm equatorial waters and take up a great deal of water vapour.

• They hit the Western Ghats and the rain bursts out.

• The moist winds strike the Western Ghats and are pushed up.
• Rising air cools. Its water vapour turns into cloud.
• Heavy rain pours on the side facing the wind (the windward side), with thunder and lightning.

What makes it a "burst"

• Sudden start: heavy rain begins all at once. It does not build up slowly.
• Violent weather: strong thunder and lightning come with the first heavy showers.
• Sharp cooling: day temperatures fall by 5–8°C between mid-June and mid-July.
• Two names: NCERT calls it the "burst" or the "break" of the monsoon. Do not mix this up with a "break in the monsoon" (see below).

Conditions it needs

• A strong pressure difference: low pressure over the heated land and higher pressure over the cooler ocean.
• Moisture-laden southwest winds that have crossed warm seas.
• A mountain barrier across the wind's path, the Western Ghats, which forces the air to rise quickly.

Where it occurs

• West coast, first week of June: the coasts of Kerala, Karnataka, Goa and Maharashtra, in that order from south to north.
• Interior parts of India: may have to wait until about the first week of July for the burst.
• Windward slopes of the Western Ghats: get the heaviest burst rain, because the winds are forced up the hills here.
• Context for timing:
• Monsoon rain first reaches the south Andaman Sea (normal date about 22 May) [2].
• Normal onset over Kerala is 1 June [5].

• Mumbai and Kolkata get the monsoon about 10–13 June (NCERT).

• Arabian Sea branch: carries the rain to the west coast and central India [4]. This is the branch that causes the burst on the western coasts.

Don't confuse with

• Onset of the monsoon: the official declaration by IMD that the monsoon has reached Kerala (normal date 1 June). IMD checks clouds, wind depth, wind speed and rain to declare it [5]. The burst is the weather event itself: the sudden, violent first heavy rain.
• Break in the monsoon: a dry spell of days or weeks during the rainy season. The "break" or burst of the monsoon is the start of heavy rain, not a pause in it.
• Advance of the monsoon: the gradual spread of the monsoon over the whole country, from Kerala on 1 June to full coverage by 8 July (IMD normal after the 2020 revision; earlier 15 July) [3]. The burst is the sudden event at each place along the way.
• First arrival of monsoon rain: the monsoon first appears over the Andaman Sea (about 22 May) [2]. The famous burst happens later, on the west coast in early June.

Prelims Hooks

• Burst of the monsoon = sudden start of heavy rain with thunder and lightning, not a gradual increase. NCERT also calls it the "break" of the monsoon.
• Order of the burst (first week of June): coasts of Kerala → Karnataka → Goa → Maharashtra. Interior parts may wait until the first week of July.
• Temperature effect: day temperatures fall by 5–8°C between mid-June and mid-July.
• Cause–landform pair: moist southwest winds + Western Ghats → air forced up → heavy rain on the windward side.
• Trap: the burst of the monsoon (start of rain) is not the same as a break in the monsoon (dry spell within the season).
• Trap: the monsoon reaches the Andaman Sea (about 22 May) before Kerala, so Kerala is not the first place to get monsoon rain [2].

Mains Points

• Farming and the economy (GS-I/III): about 75 per cent of India's rain falls in the southwest monsoon [4]. The burst on the west coast signals that kharif sowing can start.
• If the burst comes late or is weak, sowing is delayed and reservoirs stay low.

• Onset over Kerala has ranged from 24 May (2025) to 8 June (2016, 2019) [2][5]. So farm plans should follow the actual onset, not a fixed calendar date.

• Relief from heat, risk of disaster (GS-I/III): the burst cools the land by 5–8°C and ends the pre-monsoon heat.

• Its sudden, heavy rain on the steep windward slopes of the Western Ghats can also cause flash floods and landslides along the Kerala–Karnataka–Goa–Maharashtra coast. Early warning is therefore important.

• Relief as a control on rain (GS-I): the burst shows how landforms shape climate.

• The Western Ghats force the moist winds to rise, so the west coast gets a sudden, heavy burst.
• Interior areas lie on the side away from the wind (the leeward side). They get their rain later and in smaller amounts.

Related concepts

• Monsoon theories
• Southwest monsoon
• Onset of the monsoon

Read more

• How the monsoon works: theories, onset, burst and advance