Onset and retreat of monsoon

1. Compiled By - Dr. Bheekam Singh
Part 2

2. Onset of Monsoon
Retreat of Monsoon

3. Onset of Monsoon
• Monsoon in India lasts for 100-120 days
• From early June to mid September
• Before entering into India monsoon winds encounters with many
atmospheric conditions all the way
• So these winds are pulsating in nature and not steady
• So monsoon arrives with sudden down pour of rainfall continues to
several days

4. Burst of Monsoon
• This sudden onset of monsoon with heavy rainfall is known as ‘Burst
of Monsoon’.

5. Arrives in India on 1st of june
Kerala receives firs rainfall

6. South West monsoon reaching India
Divides in two parts at the start of peninsula
1. From Arabian sea side 2. BOB side

7. The Arabian sea branch reaches Mumbai around 10 days
later , at Saurashtra and Kachach in mid of June and
further to central parts of the country

8. BOB branch reach Assam on 1st week of June and after
striking with mountains reflected to Ganga Plain

9. Both Branched merge at North Western Ganga Plain and
provide rainfall there
Rainfall in Delhi in last June or precisely on 29th june is the
gift of BOB branch

10. In first week of July reaches to Punjab, W. UP, Haryana nd
Eastern Rajasthan

11. By mid July reach to Himachal and further north parts of
India

12. Retreating of Monsoon
• Also known as ‘North east Monsoon’.
• High Pressure starts to begin over north India
• Wind moves towards south
• Starts in early Sep
• Retreat is more gradual than onset
• Begins in northwestern states of India

13. Starts from north western states in September

14. Reaches north of the peninsula in Mid
October
And windrow very fast in south parts of
peninsula
Windrows completely in early Dec

15. Islands receives Monsoon rainfall from 1st
of April to 1st week of May
Widrawal take place from 1st week of Dec
to 1st week of Jan

16. While retreating take moisture from Arabian sea and BOB
and provides second round of rainfall called ‘Winter
Monsoon’
Generally in eastern parts of peninsula

17. Break in Monsoon
• During the south west Monsoon after having rains for several weeks
the rain fails to occur for one or more weeks called ‘break in
monsoon’.
• These dry spells of monsoon are having different names and reasons
in different regions:
• In northern India fail if the rain bearing storms are not very frequent
along the monsoon trough or ITCZ
• Over the west coast they are associated with the flow of wind parallel
to western ghats

18. Mango Shower
• Towards the end of summer there are pre monsoon showers in Kerala
and coast of Karnataka
• Locally known as Minnesota
• Help in ripening of mangoes

19. Blossom Shower
• In late march or April there are showers in Kerala and near by areas
• These showers helps in blossom of coffee flowers

20. Nor westers
• Originate in the form of thunderstorms at Chota Nagpur region and
flow towards north east
• Provide rainfall in West Bengal and Assam
• Their nature can be understand by the local name ‘Kalbaisakhi’ or
calamity in the month if Baisakh
• Useful for the cultivation of tea, rice and jute
• Also called ‘Bardoli Cheerah’ in Assam

21. Western disturbances
• “a low pressure area or a trough over surface or
the upper-air in the westerly winds regime,
north of 20°N, causing changes in pressure, wind
pattern and temperature fields. It is
accompanied by cloudiness, with or without
precipitation.”
• WDs originate in the Caspian Sea or the
Mediterranean Sea as extra-tropical cyclones.
• They gradually travel across the middle-east
from Iran, Afghanistan and Pakistan to enter the
Indian sub-continent.
• Though WDs move across the Indian region

22. over Northwest India including Punjab, Haryana, Uttar Pradesh and Delhi. Their effect
sometime extends up to Gangetic plains and Northeast India.
They are also responsible for bringing snowfall in the higher reaches of Jammu & Kashmir,
Himachal Pradesh and Uttarakhand.
Important for the development of Rabi Crops specially wheat