Disaster/Flood preparedness for

monsoon, special emphasis on

monsoon -2020

Dr. Jayanta Sarkar

IMD Gujarat

Summary of the Forecast Assessment: SW

Monsoon season 2020

a) Southwest monsoon seasonal (June to September) rainfall over the

country as a whole is likely to be normal (96-104%).

b) 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.

c) 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.

Summary of the Forecast Assessment: SW

Monsoon Season 2020

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 willalso be issued.

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 statistical model suggests high probability (41%) for

2020 monsoon rainfall to be normal (96-104% of LPA).

Table: 5 category probability forecasts for the Seasonal (June to September) rainfall over the country

as a whole

Forecast based on the Monsoon Mission Coupled

Forecasting System (MMCFS)

a) For generating the forecast for the 2020 southwest

Monsoon season rainfall atmospheric and oceanic initial

conditions during March2020 were used. The forecast was

computed as the average of 51 ensemble members.

b) 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).

Predictors used by IMD’s SEFS for April Forecast for the

seasonal rainfall over the country as a whole:

S.No Predictor Period

1 SST Gradient Between

Northeast Pacific and

Northwest Atlantic

(December +January)

December

+January

2 Equatorial SE Indian

Ocean Sea Surface

Temperature

February +

March

3 East Asia Mean Sea

Level Pressure

February +

March

4 NW Europe Land Surface

Air Temperatures

January

5 Equatorial Pacific Warm

Water Volume

February

+March

7

April

June

All India June – September Rainfall

Update for All India June – September Rainfall

All India Monthly(July & August) Rainfall

June – September Rainfall for Four Geographical Regions

In addition, Forecast for Date of Monsoon Onset over Kerala in May

Month of Forecast Issue

All India Second Half of SeasonAugust - September Rainfall

All India MonthlySeptember Rainfall

July

August

All India

Geographical Regions

Operational Long Range Forecast For

the Southwest Monsoon Issued By IMD

2-Stage Forecast System for

All India (Nation-wide) Seasonal Rainfall

April

June

All India June – September

Rainfall

Update for All India June – September

RainfallJune

1st Stage

Forecast based

on 5 predictors

requiring data

up to March

2nd Stage

Forecast based

on 6 predictors

requiring data

up to May

IOD and ELNINO scenario 2020 (JAPAN)

El Niño Modoki-like state has been observed. The SINTEX-F (fig a) predicts that

the tropical Pacific will return to a neutral-state from summer.

SINTEX – F (FIG B)showsThe strong positive Indian Ocean Dipole disappeared.

Now, the whole tropical Indian Ocean is warmer-than-normal. The model predicts the

evolution of another moderately positive Indian Ocean Dipole from northern summer.

There is a large uncertainty in the prediction at present due to the large spread in the

prediction plumes of the dipole mode index.

Fig a)Fig b)

IOD and ELNINO scenario 2020 (BOM)

a) The El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) both

remain neutral. Neutral ENSO conditions are likely to persist over the coming months,

with some likelihood a La Niña-like state could develop in the tropical Pacific Ocean

late in the northern hemisphere summer (less than 50% chance).

b) Most models suggest a negative IOD could develop in the Indian Ocean from mid-

summer.

IOD and ELNINO scenario 2020 (IMD FCST)

The probability forecast for ENSO indicates enhanced probability for

neutral ENSO conditions up to MJJ season. Enhanced probability for La Niña

conditions is predicted from JJA season onwards. Thus, forecast indicates

enhanced probability for development of La Niña conditions during end of the

forecast period.

The probability forecast for IOD (Fig.5b) indicates nearly equal

probabilities for neutral and positive IOD conditions up to MJJ season and JJA

season onwards enhanced probability for negative IOD conditions is predicted.

JJAS rainfall Climatology

JJAS rainfall anomalies during El-Nino years

1982 1986

1987 1991

JJAS rainfall anomalies during La-Nina years

1988 1998

2007 2010

JJAS rainfall anomalies during El-Nino + IOD

years

1994 1997

2006

Consensus Statement on the Forecast for the 2020 Southwest Monsoon Season

(June – September) Rainfall over South Asia

Fig. Probability of the most likely category for the 2020

southwest monsoon rainfall over South Asia.

The outlook suggests that the rainfall for

the season as a whole is most likely to be

normal during the 2020 southwest

monsoon season (June – September) over

most parts of South Asia. Above-normal

rainfall is most likely over the southern

parts and some areas of north-western

parts of the region. However, the seasonal

rainfall over land areas around the north

Bay of Bengal and some northern most

areas of the region is most likely to be

below normal. The seasonal rainfall is most

likely to be normal over the remaining

areas.

INFORMATION DISSEMINATION

• Telephone

• Fax

• Police wireless (VHF)

• Website

• Email

• Electronic and Print media (AIR/DD/Private

Channels)

• SMS

• Community Radio (FM RADIO)

• Whats App

• Facebook/ Twitter

India Meteorological Department 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.

• 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.

India Meteorological Department New Normal Dates of

Onset/Progress and Withdrawal of Southwest Monsoon over India

• Monsoon onset over Kerala remains the same,

i.e., 1 June.

• New monsoon advance dates over the state like

Gujarat is delayed by 6-11 days compared to

existing normal dates.

• Extreme northwest India, the monsoon arrives

now little earlier, on 8th July compared to the

existing date of 15th July.

India Meteorological Department New Normal Dates of

Onset/Progress and Withdrawal of Southwest Monsoon over India

Fig. 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).

Sr. No.

Station Name Normal Monsoon

Onset/ Progress

Date New Existing

(1961- 2019)

(1901- 1940)

1 Thiruvananthapuram, Kerala 01-June 01-June

2 Surat, Gujarat 19-June 13-June

3 Ahmedabad, Gujarat 21-June 14-June

4 Bhuj, Gujarat 30-June 21-June

5 Surendranagar,Gujarat 26-June 15-June

India Meteorological Department New Normal Dates of

Onset/Progress and Withdrawal of Southwest Monsoon over India

Fig. 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).

Sr. No.

Station Name Normal Monsoon

Withdrawal

Date New Existing

(1971- 2019)

(1901- 1940)

1 Surat, Gujarat 2-October 25-September

2 Ahmedabad, Gujarat 30-September 22-September

3 Bhuj, Gujarat 26-September 15-September

4 Surendranagar,Gujarat 27-September 20-September

EXPECTED RF SCENARIO IN THE FIRST

WEEK OF JUNE,

2020

Thank You