Ministry of Earth Science

IMD announces that it expects monsoon rainfall to be normal this year

Issues the first stage long range forecast for south-west monsoon season rainfall

Monsoons are expected to hit Thiruvananthapuram in Kerala on June 1

Posted On: 15 APR 2020 3:25PM by PIB Delhi

The India Meteorological Department (IMD) today announced that it expects monsoon rainfall to be normal this year. "Southwest monsoon seasonal (June to September) rainfall over the country as a whole is likely to be normal (96-104%)," the IMD said in its first stage Long Range Forecast (LRF) for monsoons.

Addressing a press conference through video link, Secretary of Ministry of Earth Sciences Dr. M. Rajeevan released the IMD’s Long Range Forecast for the 2020 Southwest Monsoon Season Rainfall.  Director General of IMD, Dr. M. Mohapatra was also present.

The IMD also issued the ‘New Normal Dates of Onset/Progress and Withdrawal of Southwest Monsoon Over India’.

DR. Rajeevan  said that quantitatively, the monsoon seasonal (June to September) rainfall is likely to be 100% of the Long Period Average (LPA) with a model error of 5%. The LPA of the season rainfall over the country as a whole for the period 1961-2010 is 88 cm.

"Good news is that it is estimated that the deficient rainfall will be 9 per cent. This forecast is based on the statistical model, it suggests that we will have a normal monsoon", he said.

He said, IMD will issue the updated forecasts in the last week of May/first week of June 2020 as a part of the second stage forecast.

Dr. Rajeevan pointed out that “ Neutral El Nino Southern Oscillation (ENSO) conditions are prevailing over the Pacific Ocean and Neutral Indian Ocean Dipole (IOD) conditions are prevailing over the Indian Ocean. Some climate model forecasts indicate these conditions are likely to persist during the ensuing monsoon season”. “As sea surface temperature (SST) conditions over the Pacific and Indian Oceans are known to have strong influence on Indian monsoon, IMD is carefully monitoring the evolution of sea surface conditions over the Pacific and the Indian oceans,” he added. 

Dr. Rajeevan said that La Nina, or cooler-than-usual sea surface temperatures in the east-central Pacific Ocean, is typically associated with better monsoon rains and colder winters in India while El Nino is associated with below-normal rainfall in the country.

The southwest monsoon season, that replenishes the country's farm-dependent economy, first hits the southern tip of Kerala usually in the first week of June and retreats from Rajasthan by September.

Monsoons are expected to hit Kerala's Thiruvananthapuram on June 1. In states like Maharashtra, Gujarat, Madhya Pradesh, Chattisgarh, Telegana, Andhra Pradesh, Odisha, Jharkhand, Bihar and parts of Uttar Pradesh, monsoon will be delayed by 3-7 days compared to the existing normal dates.

However, over extreme northwest India, the monsoon arrives now little earlier, on 8th July compared to the existing date of 15th July.

Monsoons are expected to withdraw in south India on October 15.

Given below are details:

 

Summary of the Forecast for the 2020 Southwest Monsoon Rainfall

  1. Southwest monsoon seasonal (June to September) rainfall over the country as a whole is likely to be normal (96-104%).

  2. Quantitatively, the monsoon seasonal (June to September) rainfall is likely to be 100% of the Long Period Average (LPA) with a model error of ± 5%.  The LPA of the season rainfall over the country as a whole for the period 1961-2010 is 88 cm.

  3. Neutral El Nino Southern Oscillation (ENSO) conditions are prevailing over the Pacific Ocean and Neutral Indian Ocean Dipole (IOD) conditions are prevailing over the Indian Ocean.  Some climate modelforecasts indicatethese conditions are likely to persist during the ensuing monsoon season.  However, a few other global climate models indicate possibility of development of weak La Nina conditions over the Pacific Ocean during thesecond half of the season.

As sea surface temperature (SST) conditions over the Pacific and Indian Oceans are known to have strong influence on Indian monsoon, IMD is carefully monitoring the evolution of sea surface conditions over the Pacific and the Indian oceans.

IMD will issue the updated forecasts in the last week of May/ first week of June2020 as a part of the second stage forecast. Along with the updated forecast, separate forecasts for the monthly (July and August) rainfall over the country as a whole and seasonal (June-September) rainfall over the four broad geographical regions of India will also be issued.

1.         Background

India Meteorological Department (IMD) issues operational forecast for the southwest monsoon season (June to September) rainfall for the country as a whole in two stages. The first stage forecast is issued in April and the second stage forecast is issued in May/June. These forecasts are prepared using the state-of-the-art Statistical Ensemble Forecasting system (SEFS) that is critically reviewed and improved regularly through in-house research activities.  Since 2012, IMD is also using the dynamical global climate forecasting system (CFS) model developed under the Monsoon Mission to generate experimental forecasts. For this purpose, the latest version of the Monsoon Mission CFS (MMCFS) model was implemented in January 2017 at the Office of Climate Research and Services, IMD, Pune.

IMD’s SEFS model for the April forecast uses the following 5 predictors that require data upto March.

S. No                            Predictor                                                                                   Period

1          The   Sea Surface Temperature (SST) Gradient between

             North Atlantic  and  North Pacific                                                           December + January

2          Equatorial South Indian Ocean SST                                                        February

3          East Asia Mean Sea Level Pressure                                                       February + March

4          Northwest Europe Land Surface Air Temperature                                     January

5          Equatorial Pacific Warm Water Volume                                                   February + March

2.         Forecast For the 2020 Southwest monsoon Season (June–September) rainfall over the Country as a whole

2a.        Forecast based on the Monsoon Mission Coupled Forecasting System (MMCFS)

For generating the forecast for the 2020 southwest Monsoon season rainfall atmospheric and oceanic initial conditions during March 2020 were used.  The forecast was computed as the average of 51 ensemble members.

The forecast based on the MMCFS suggests that there is a high probability (70%) for 2020 monsoon rainfall to be above normal to excess (More than 104% of LPA).

2b.        Forecast Based on the Operational Statistical Ensemble Forecasting System

a)         Quantitatively, the monsoon seasonal rainfall is likely to be 100% of the Long Period Average (LPA) with a model error of ± 5%.  The LPA of the season rainfall over the country as a whole for the period 1961-2010 is 88 cm.

(b)The 5 category probability forecasts for the Seasonal (June to September) rainfall over the country as a whole is given below:

Category           Rainfall Range(% of LPA)           Forecast Probability (%)        Climatological Probability (%)

Deficient                       < 90                                                      9                                  16

Below Normal                90 - 96                                                  20                                 17

Normal                          96 -104                                                 41                                 33

Above Normal                104 -110                                                21                                 16

Excess                         > 110                                                    9                                  17

           

The statistical model suggests high probability (41%) for 2020 monsoon rainfall to be normal (96-104% of LPA).

3.         Sea Surface Temperature (SST) Conditions in the equatorial Pacific & Indian Oceans

            Currently, El Nino Southern Oscillation (ENSO) neutral conditions are prevailing over the Pacific Ocean. The latest forecasts from some global climate models indicate neutral ENSO conditions are likely to persist during the monsoon season. However, few other global climate models including MMCFS indicate possibility of development of weak LaNina conditions over the Pacific Ocean. It may be mentioned that the global climate model predictions prior to and during the spring season generally have noticeable uncertainty due to spring barrier in the seasonal predictability.

At present, neutral Indian Ocean Dipole (IOD) conditions are prevailing over the Indian Ocean. The latest forecast from the MMCFS and global models together indicate neutral IOD conditions are likely to persist during the season.

New Normal Dates of Onset/Progress and Withdrawal of Southwest Monsoon over India

 

The present normal monsoon onset and withdrawal dates are based on records of only a few stations (149 stations) during the period 1901-1940.

 

India Meteorological Department (IMD) has now revised the normal onset and withdrawal dates based on recent data. The normal dates of onset are revised based on data during 1961-2019 and normal dates of withdrawal are revised based on data during 1971-2019.

 

IMD has designed new objective criteria for defining monsoon onset over the entire country based on daily gridded (1ox1o) rainfall data set. The new objective criteria used for deciding  monsoon onset/progress dates are designed so as to closely simulate IMD’s operational onset dates. However, the new withdrawal dates are fixed using the IMD’s operational withdrawal dates during 1971-2019.

Monsoon onset over Kerala remains the same, i.e., 1 June. However, new monsoon advance dates over the states like Maharashtra, Gujarat, Madhya Pradesh, Chattisgarh, Telegana, Andhra Pradesh, Odisha, Jharkhand, Bihar and parts of Uttar Pradesh are delayed by 3-7 days compared to existing normal dates. However, over extreme northwest India, the monsoon arrives now little earlier, on 8th July compared to the existing date of 15th July. There are however appreciable changes in the monsoon withdrawal dates, especially over Northwest and Central India. Monsoon withdraws from NW India almost 7-14 days later from the existing dates. There is no change in the final withdrawal date over south India, i.e., 15th October.

 

These new dates are relevant for many applications like agriculture, water and power management etc.

 

The new and older onset and withdrawal dates are shown in Fig 1.

 

Table -1 shows new and old onset and withdrawal dates of few major cities in India. IMD will start using these new dates from 1 June 2020. IMD will release a very detailed report by 15 May 2020.

 

Existing & New Dates of Normal Monsoon Onset/progress

Fig.1(a) Map showing the new (black solid) normal dates of monsoon onset/progress over the country based on the new objective rainfall criteria for the base period of 1961-2019 along with existing normal dates (red dotted). 

 

 

Existing & New Dates of Normal Monsoon Withdrawal

 

 

 

 

Fig.1(b) Map showing the new (black solid) normal dates of monsoon withdrawal over the country based on the new objective rainfall criteria for the base period of 1971-2019 along with existing normal dates (red dotted). 

 

Table-1: Normal monsoon onset (1961-2019) dates based on new rainfall criteria and withdrawal (1971-2019) dates based on the operational data over a few major cities of the country.

 

Sr. No.

Station Name

Normal Monsoon

Onset/ Progress Date

Normal Monsoon Withdrawal Date

New

(1961-2019)

Existing

(1901-1940)

New

(1971-2019)

Existing

(1901-1940)

1

Thiruvananthapuram, Kerala 

01-Jun

01-Jun

*

*

2

Chennai, Tamil Nadu

04-Jun

01-Jun

*

*

3

Udupi, Karnataka 

04-Jun

05-Jun

*

*

4

Panjim, Goa, 

07-Jun

07-Jun

14-Oct

10-Oct

5

Gangawati, Karnataka

06-Jun

05-Jun

15-Oct

*

6

Ongole, Andhra Pradesh 

08-Jun

04-Jun

*

*

7

Hyderabad

08-Jun

07-Jun

14-Oct

15-Oct

8

Machilipatnam, Andhra Pradesh 

13-Jun

05-Jun

*

*

9

Kolhapur, Maharashtra 

09-Jun

09-Jun

11-Oct

01-Oct

10

Satara, Maharashtra 

10-Jun

09-Jun

09-Oct

30-Sep

11

Pune, Maharashtra 

10-Jun

09-Jun

11-Oct

06-Oct

12

Jagdalpur,Chhattisgarh

13-Jun

09-Jun

13-Oct

15-Oct

13

Vizag, Andhra Pradesh 

11-Jun

09-Jun

14-Oct

15-Oct

14

Mumbai, Maharashtra 

11-Jun

10-Jun

08-Oct

29-Sep

15

Ahmednagar, Maharashtra 

12-Jun

10-Jun

08-Oct

29-Sep

16

Cuttack, Odisha

12-Jun

11-Jun

12-Oct

13-Oct

17

Puri, Odisha 

13-Jun

12-Jun

12-Oct

13-Oct

18

Surat, Gujarat

19-Jun

13-Jun

2-Oct

25-Sep

19

Jalgaon, Maharashtra 

18-Jun

13-Jun

6-Oct

27-Sep

20

Nagpur,  Maharshtra

15-Jun

13-Jun

6-Oct

6-Oct

21

Raipur, Chhattisgarh

16-Jun

13-Jun

9-Oct

10-Oct

22

Ahmedabad

21-Jun

14-Jun

30-Sep

22-Sep

23

Khandwa, Madhya Pradesh 

20-Jun

14-Jun

3-Oct

25-Sep

24

Bilaspur, Chhattisgarh

16-Jun

14-Jun

7-Oct

7-Oct

25

Jamshedpur, Jharkhand

14-Jun

12-Jun

10-Oct

12-Oct

26

Kolkata, West Bengal 

11-Jun

10-Jun

12-Oct

14-Oct

27

Aizawl, Mizoram

5-Jun

1-Jun

14-Oct

15-Oct

28

Bhuj, Gujarat

30-Jun

21-Jun

26-Sep

15-Sep

29

Surendranagar,Gujarat

26-Jun

15-Jun

27-Sep

20-Sep

30

Bhopal, Madhya Pradesh 

22-Jun

15-Jun

30-Sep

20-Sep

31

Varanasi, Uttar Pradesh 

20-Jun

15-Jun

5-Oct

6-Oct

32

Agartala, Tripura 

4-Jun

1-Jun

14-Oct

15-Oct

33

Shillong

5-Jun

1-Jun

14-Oct

15-Oct

34

Imphal, Manipur

5-Jun

1-Jun

15-Oct

15-Oct

35

Gaya, Bihar

16-Jun

12-Jun

8-Oct

12-Oct

36

Siliguri, West Bengal 

8-Jun

9-Jun

12-Oct

14-Oct

37

Tripura

4-Jun

2-Jun

14-Oct

14-Oct

38

Guwahati, Assam

4-Jun

2-Jun

14-Oct

15-Oct

39

Dimapur, Nagaland

4-Jun

2-Jun

14-Oct

15-Oct

40

Ajmer, Rajasthan

1-Jul

23-Jun

21-Sep

12-Sep

41

Dholpur, Rajasthan

28-Jun

20-Jun

29-Sep

25-Sep

42

Lucknow

23-Jun

20-Jun

3-Oct

30-Sep

43

Azamgarh, Uttar Pradesh 

20-Jun

17-Jun

4-Oct

5-Oct

44

Chhapra, Bihar

18-Jun

13-Jun

6-Oct

10-Oct

45

Gangtok, Sikkim, 

10-Jun

10-Jun

9-Oct

14-Oct

46

Jalpaiguri, West Bengal 

7-Jun

9-Jun

12-Oct

14-Oct

47

Tezpur, Assam

5-Jun

3-Jun

14-Oct

14-Oct

48

Jaisalmar, Rajasthan

8-Jul

15-Jul

17-Sep

1-Sep

49

Jaipur, Rajasthan

1-Jul

23-Jun

22-Sep

12-Sep

50

Agra, Uttar Pradesh 

30-Jun

23-Jun

14-Sep

22-Sep

51

Itanagar, Arunachal Pradesh

5-Jun

4-Jun

14-Oct

14-Oct

52

Dibrugarh, Assam

4-Jun

3-Jun

14-Oct

14-Oct

53

Bikaner, Rajasthan

5-Jul

13-Jul

17-Sep

1-Sep

54

Churu, Rajasthan

4-Jul

6-Jul

19-Sep

10-Sep

55

Sonepat, Haryana

30-Jun

30-Jun

23-Sep

15-Sep

56

New Delhi

27-Jun

23-Jun

25-Sep

22-Sep

57

Bhiwani, Haryana

3-Jul

6-Jul

21-Sep

12-Sep

58

Pithoragarh, Uttarakhand

20-Jun

21-Jun

28-Sep

27-Sep

59

Shimla, Himachal Pradesh

24-Jun

23-Jun

24-Sep

22-Sep

60

Jalandhar, Punjab 

28-Jun

13-Jul

21-Sep

10-Sep

61

Chandigarh 

26-Jun

1-Jul

22-Sep

22-Sep

62

Jammu, 

28-Jun

13-Jul

21-Sep

20-Sep

63

Srinagar-Kyonon Road, Ladakh

22-Jun

22-Jun

24-Sep

30-Sep

64

Ladakh, Ladakh

23-Jun

26-Jun

23-Sep

29-Sep

*SW Monsoon retreats from the area and Northeast monsoon gets established

 

*****

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