Monsoon - 2015

Dr. K.K. Singh

Head, Agromet

Long range forecast

The first stage operational forecasts for the southwest monsoon season (June – September) rainfall are issued on 22 April 2015

Quantitatively, the monsoon seasonal rainfall is likely to be 93% 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 1951-2000 is 89 cm.

Sl. 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

5 category probability forecasts for the Seasonal (June to September) rainfall over the country as a whole

 Category

Rainfall Range(% of LPA)

ForecastProbability (%)

ClimatologicalProbability (%)

Deficient < 90 33 16

Below Normal 90 - 96 35 17

Normal 96 -104 28 33

Above Normal 104 -110 3 16

Excess > 110 1 17

Forecast of the Onset Date of Southwest Monsoon - 2015 over Kerala using statistical model

The southwest monsoon is likely to set over Kerala on 30th May

with a model error of ± 4 days. Forecast issued on 14 May 2015

6 predictors used are:

1. Minimum Temperature over North-west India

2. Pre-monsoon rainfall peak over south Peninsula

3. Outgoing Long wave Radiation (OLR) over south China Sea

4. Lower tropospheric zonal wind over southeast Indian ocean

5. Upper tropospheric zonal wind over the east equatorial Indian

Ocean

6. Outgoing Long wave Radiation (OLR) over south-west Pacific

region

The operational forecasts for the event issued during all the last nine years (2005 to 2014)

YearActual Onset Date

Forecast Onset Date

2005 7th June 10th June

2006 26th May 30th May

2007 28th May 24th May

2008 31st May 29th May

2009 23rd May 26th May

2010 31st May 30th May

2011 29th May 31st May

2012 5th June 1st June

2013 1st June 3rd June

2014 6th June 5th June

The Northern Limit of Monsoon (NLM) continue to pass through Lat 06.0°N/ Long. 60.0°E,  06.0°N/ Long. 70.0°E, Lat. 07.0°N/Long. 80.0°E, Lat. 10.0°N/ Long. 86.0°E, Lat. 13.0°N / Long. 89.0°E and Lat. 18.0°N / Long. 95.0°E.

Rainfall for previous week Rainfall for the period 01 to 27 May

Current Forecast

During the past 24 hours, winds in the lower tropospheric

levels have become more westerlies/south westerlies 

leadinging to down stream convergence and increase in rainfall over Lakshadweep area and southern parts of

 peninsular India. 

Persistence of convection indicates that conditions are 

becoming favourable for the onset of southwest monsoon over Kerala around 5th June.

ENSO Forecast

Model ENSO predictions

Extended Range Forecast (ERF)

Outlook for June 2015

Issued by NWP Division, IMD, New Delhi27 May, 2015

(Forecast for June 2015)

IITM’s GFSv2bcBased on Initial Condition of Pentad close to Wednesday(11 members), T126L64 (3),(11 members), T126L64 (4),

Regrid into 0.5x0.5

Calculate daily anomaly for all the three models based

on corresponding model hindcast

climatology

Prepare weekly mean and anomaly rainfall for 4 weeksOn Every Thursday

valid from Friday

MME : Based on 6 Models Outputs

Anomaly for

Month 1

Current Multi-model ensemble extended range forecastCurrent Multi-model ensemble extended range forecastIITM’s CFSv2

Based on Initial Condition of Pentad close to Wednesday(11 members), T382L64 (1)(11 members), T126L64 (2)

JMA’s Ensemble Prediction System (EPS) Based on

Wednesday(50 members), T159L60 (5)

NCEP CFSv2 Based on Wednesday

(16 members), T126L64 (6)

IC=26 May

IC=26 May

IC=27 May

IC=27 May

MME forecast mean & anomaly rainfall for June 2015 , IC = 27 May, 2015

AISMR = -21.29

NE India = -11.77

NW India = -25.39

CE India = -39.32

SP India = -7.24

MME forecast mean & anomaly rainfall for June 2015 , IC=27 May, 2015

Summary The experimental forecast for June 2015 indicates close

to deficient rainfall for June 2015 with an all India departure of -21%. (SD for June is about 23%).

Monsoon progress is likely to be slow.

We must also understand the limited forecast skill for the monthly forecast and it is only a broad outlook, which is being prepared as required by many users.

Weekly rain forecast during June 2015

Weekly rain forecast during June 2015

Real-time forecast based on 31st May 2015 initial condition

This MME forecast has been prepared using the CFS (T126 & T382) and GFSbc (T126 & T382) (each 11 members) .

Daily evolution of rainfall and wind at 850hPa (by MME)

After onset the LPS is likely to intensify and move towards Oman coast. This system may dissipate around 11th June and till then the monsoon activity will be weaker than normal over India.

It is likely that by 17th June the offshore trough along the west coast will be established and thereafter monsoon trough will start establishing over the Gangetic plains.

The rainfall will be mainly confined to North-East and southern peninsula for the next 10-15 days.

Large-scale MISO also indicates north-ward propagation of convection from southern ocean to peninsula in next 15 days and weakening thereafter.

Convection associated with MJO is expected to move eastward to the Indian ocean till 12th June, however further movement to the maritime continent is not favoured due to El Nino induced strong convection towards central Pacific.

Key points from the present forecast

Daily evolution of minimum and maximum temperature (by MME)

Daily evolution of minimum and maximum temperature Anomaly (by MME)

Predicted pentad wise temperature anomaly (by MME)

Predicted pentad wise rainfall (by MME)

Experimental ERFS Forecast for June and JJAS - 2015 with May Start

General Circulation Models (GCMs) used for the experimental forecast:

• CCM3v6 (24 members) 

• ECHAM4p5_CA_SST (24 members)

• ECHAM4p5_CFS_SST (24 members)

• CFSV2 (24 members)

• COLA-RSMAS-CCSM3(6 members)

• GFDL_CM2p1_aer04(10 members)

• GFDL-CM2p5-FLOR-A06 (12 members)

• GFDL-CM2p5-FLOR-B01 (12 members)

• IMD-SFM(10 members)

• ECMWF(15 members)

• IITM-ERPAS (43 members that is only used as one of the product in monthly deterministic

forecast)

 

Precipitation Forecast for June (lead 1) - 2015

In allusion of deterministic precipitation forecast, normal rains are recognized to have in all parts of the country except HP, Uttarakhand, Entire UP, Bihar, East MP, Chhattisgarh, Orissa, Vidarbha, Gangetic WB, Jharkhand, and Saurashtra & Kutch where deficit rainfall is expected. On the other hand, excess rainfall is expected over West Rajasthan, SI Karnataka, Rayalseema, Tamilnadu. For the country as a whole, the forecast of precipitation is expected about 94% of long period average (LPA).

In reference of probabilistic rainfall forecast, signals of below normal precipitation are prevailing over Uttarakhand, East UP, Bihar, SHWB, Gangetic WB, Jharkhand, Telangana, Marathwad, East MP, Chhattisgarh, Orissa, Vidarbha. Probability of excess rainfall is high over East Rajasthan, J&K, HP, Punjab, Assam& Meghalaya, NI & SI Karnataka, Rayalseema, Tamilnadu and Kerala, Konkan &Goa, Coastal Karnakata. There is absence of any clear signals for the remaining parts of the country. At all India level, probability for near normal rainfall is high.

Precipitation Climatology (mm/day) for June Probabilistic Precipitation Forecast for June (lead 1)- 2015 (IITM-ERPAS is not included)

Deterministic Precipitation Forecast (percentage departure) for JJAS (lead 1) -2015

In allusion of deterministic precipitation forecast, normal rains are recognized to have in all parts of the country except Punjab, Haryana, CHD & Delhi, Uttrakhand and Entire UP where deficit rainfall is expected.

Whereas, excess rainfall is expected over Kerala. For the country as a whole, the forecast of precipitation is expected about 96% of long period average (LPA).

Precipitation Climatology (mm/day) for JJAS Probabilistic Precipitation Forecast for JJAS (lead 1)- 2015

In reference of probabilistic rainfall forecast, signals of below normal precipitation are prevailing over Punjab, Haryana, CHD & Delhi, Uttarakhand, Entire UP, Bihar, East MP, SHWB, Assam & Meghalaya. Probability of above normal rainfall is high over J&K, Arunachal Pradesh, NMMT, Jharkhand, Orissa, West MP, Madhya Maharashtra, Konkan & Goa, NI Karnataka, Kerala and Tamilnadu. At all India level, probability for near normal rainfall is high.

Performance of ERFS Forecast – Month wise 2009-2014

JUNE JULY

Performance of ERFS Forecast – Month wise 2009-2014 cont..

AUGUST SEPTEMBER

JJAS 2009-2014

Performance of ERFS Forecast – Seasonal 2009-2014

Confidence Map in ERFS for real time prediction of summer monsoon season from 2009-14

JUNE

JULY

AUGUST SEPTEMBER

No of subdivisions matched in

observed rainfall

category

Experimental ERFS

JJAS 24

June 11

July 18

August 17

September 14

Confidence Map in ERFS for real time prediction of summer monsoon season from 2009-14

JJAS