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Salient Features of Monsoon 2021 - 30th September, 2021, 1730 hrs IST

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Government of India
Ministry of Earth Sciences
India Meteorological Department

  • The southwest monsoon seasonal rainfall during June to September for the country as a whole has been normal (96 -104% of LPA).

  • Quantitatively the 2021 all India monsoon seasonal rainfall during 1 June to 30 September 2021 has been 87.0 cm against long period average of 88.0 cm based on data of 1961-2010 (99% of its Long Period Average (LPA)) Fig.1.

  • The southwest monsoon seasonal (June to September) rainfall over the four homogeneous regions is Normal over Northwest India (96%) and central India (104%). Seasonal rainfall is below normal over East and Northeast India (88%) and above normal over South Peninsula India (111%). Monthly and seasonal total rainfall over four homogeneous regions and all India are given in Fig.2

  • The southwest monsoon seasonal (June to September) rainfall over the monsoon core zone, which consists of most of the rainfed agriculture regions in the country is above normal (>106% of LPA).

  • Out of the total 36 meteorological subdivisions, 20 subdivisions constituting 58% of the total area of the country received normal seasonal rainfall, 10 subdivisions received excess rainfall (25% of the total area) and 6 subdivisions (17% of the total area) received deficient season rainfall (Fig. 3). These 6 Met subdivisions which got deficient rainfall are Nagaland, Manipur, Mizoram & Tripura, Assam and Meghalaya, Arunachal Pradesh, Jammu & Kashmir and Ladakh, West Uttar Pradesh and Lakshadweep (Fig. 3). Out of these six Subdivisions, three lie in northeast India. Two Met Subdivisions which got much higher than normal rainfall in the season are Marathawada and Telangana.

  • Considering month to month rainfall variation over India as a whole, the season is very uniquely placed in the historical record for its distinct and contrasting month to month variation. The rainfall over country as a whole was 110%, 93%, 76% and 135% of LPA during June, July, August and September respectively.

  • The week to week progress of monsoon rainfall over country as a whole and cumulative rainfall in % departure is shown in Fig. 4 while spatial distribution of monthly rainfall over different Met-Subdivisions is shown in Fig. 5.

  • All India rainfall % departure for the months of August and September are shown in Fig. 6 and Fig. 7 respectively.

  • A deep depression formed during 12-15 September and cyclonic storm “GULAB” during 24-28 September. The tracks of the Cyclonic Storm and Deep Depression are shown in Fig 8. The number of low pressure systems formed during the season is shown in Table 1.

  • The formation and movement of the cyclone TAUKTAE, over Arabian Sea (during 14-19 May) and severe Cyclonic storm “YAAS” over Bay of Bengal (during 23 to 28th May) helped to increase cross equatorial flow and the onset of monsoon.

  • Subsequent features favored timely advance and monsoon covered entire country over many regions. However, monsoon cover entire country by 13th July against normal date of 8th July.

  • In July, the country received slightly below normal rainfall (94% of LPA). The weak monsoon in July was mainly due to absence of any major monsoon disturbance over Bay of Bengal. Absence of such major systems in July (Table 1) also caused the weak monsoon trough. The monsoon trough lay to the north of the normal position or close to the foot hills of Himalayas on many days. It resulted in frequent and prolonged floods over northeastern India, Bihar and adjoining areas of east Uttar Pradesh. At the same time, major parts of central India received deficient rainfall.

  • During August, many unfavorable features of monsoon appeared resulting in deficient rainfall for the country (76%). Negative Indian Ocean Dipole unfavorable for Indian monsoon prevailed during this month. Also, the absence of formation of monsoon depression and a smaller number of low pressure area (16-18 & 28-30 August) over Bay of Bengal caused this rainfall deficiency. Normally two monsoon depressions and two low pressure area forms in the month of August. Most of the days monsoon trough was located north of its normal position which cause subdued rainfall over Central Indian Region. Most of the days Madden Julian Oscillation (MJO) was in the phase 8, 1 and 2 which are unfavorable for monsoon rainfall activity. Also, there was less West Pacific Typhoon activity. Normally remnants of westward moving typhoons help to form Low Pressure Systems (LPS) over Bay of Bengal.

  • In September, the country as whole received excess rainfall due to many favourable conditions for the monsoon. The negative Indian Ocean dipole weakened during the month of August and at the same time the cold anomaly in the equatorial Pacific strengthened. There was a monsoon depression and a cyclonic storm formed in the month of September. During most of the days MJO was in the phase 3, 4 and 5 which are favorable for monsoon rainfall activity and low pressure system. More West Pacific Typhoon activity and the remnants of these westward moving systems helped to form LPS over Bay of Bengal. All the LPSs followed west/northwestward track causing good rainfall activity, especially over central India and adjoining areas.

  • The number of heavy rainfall events during the last five years is given in Table 2.
    Month-wise locations of Very Heavy Rainfall (115.6 to 204.4 mm) and Extremely Heavy Rainfall (more than 204.4 mm) reported stations for June to Sept 2021 given in Fig 9. The extremely rainfall events were more realized over Konkan and Madhya Maharashtra, North coastal Karnataka, parts of West Madhya Pradesh, East Rajasthan, south Gujarat, Odisha, coastal West Bengal and isolated places of Uttar Pradesh, Jammu, Himachal Pradesh, Uttarakhand, Bihar, sub-Himalayan West Bengal, Assam & Meghalaya.