Long Range Forecast Update for 2014 Southwest Monsoon Rainfall

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1 Earth System Science Organization (ESSO) Ministry of Earth Sciences (MoES) India Meteorological Department PRESS RELEASE New Delhi, 9 June 2014 Long Update for 2014 Southwest Monsoon Rainfall HIGHLIGHTS Rainfall over the country as a whole for the 2014 southwest monsoon season (June to September) is likely to be below normal (90-96% of. Quantitatively, monsoon season rainfall for the country as a whole is likely to be 93% of the long period average with a model error of ±4%. Region wise, the season rainfall is likely to be 85% of LPA over North-West India, 94% of LPA over Central India, 93% of LPA over South Peninsula and 99% of LPA over North-East India all with a model error of ± 8 %. The monthly rainfall over the country as whole is likely to be 93% of its LPA during July and 96% of LPA during August both with a model error of ± 9 %. 1. Background ESSO-India Meteorological Department (IMD) issues the operational long range forecasts for the southwest monsoon season (June-September) rainfall over the country as a whole in two stages; in April and in June. In June, in addition to the update for the forecast for the season rainfall over the country as a whole issued in April, forecasts for the monthly rainfall for July & August over the country as a whole, and forecast for the season rainfall for the 4 broad geographical regions of India (NW India, NE India, Central India and South Peninsula) are issued. The update forecast for the southwest monsoon season (June-September) rainfall over the country as a whole is issued using a 6-parameter Ensemble ing System. The 6 predictors used are: NE Pacific to NW Atlantic SST Anomaly Gradient (December + January), Southeast equatorial Indian Ocean Sea Surface Temperature (February), East Asia Mean Sea Level Pressure (February + March), Central Pacific (Nino 3.4) Sea Surface Temperature Tendency (March to May - December to February), North Atlantic Mean Sea Level Pressure (May) and North central Pacific 850 zonal wind gradient (May). 2. Sea Surface Temperature Conditions in the Pacific & Indian Oceans The ESSO-IITM coupled dynamical model predicts moderate El-Nino conditions in the tropical Pacific for summer months. Almost all ensembles (51 members) except one ensemble predict warm SST conditions in the Nino 3 and Nino 3.4 region. This provides confidence that

2 2 chances of El Nino occurring during monsoon are very high (more than 70%). On the other hand conditions in the tropical Indian Ocean are warmer than normal uniformly throughout the basin and therefore ruling out any possibility of positive Indian Ocean Dipole conditions in the tropical Indian Ocean during monsoon season. 3. Monsoon Mission Experimental Coupled Dynamical Model The experimental forecast based on the ESSO-IITM coupled dynamical model suggest that the monsoon rainfall during the 2014 monsoon season (June to September) averaged over the country as a whole is likely to be 96% ± 5% of long period model average (LPMA). The experimental five category probability forecasts for the 2014 monsoon season rainfall over the country as a whole using the experimental dynamical prediction system are 29% (deficient), 13% (below normal), 35% (normal), 19% (above normal) and 4% (excess). 4. The second Stage s for 2014 Southwest Monsoon Rainfall i) Seasonal (June-September) Rainfall over the country as a whole Quantitatively, the season rainfall for the country as a whole is likely to be 93% of the long period average ( with a model error of ±4%. The LPA rainfall over the country as a whole for the period is 89 cm. The 5 category probability forecasts for the Season (June to September) rainfall over the country as a whole is given below. Category Rainfall Climatological (% of Deficient < Below Normal Normal Above Normal Excess > ii) Season (June-September) Rainfall over Broad Geographical Regions The season rainfall is likely to be 85% of LPA over North-West India, 94% of LPA over Central India, and 93% of LPA over South Peninsula, and 99% of LPA over North-East India all with a model error of ± 8 %. iii) Monthly (July & August) Rainfall over the country as a whole The rainfall over the country as a whole is likely to be 93% of its LPA during July and 96% of LPA during August both with a model error of ± 9 %. More details of the operational and experimental forecast models are given in the appendix.

3 3 APPENDIX TO THE LRF PRESS RELEASE New Delhi, 9 th June Introduction Earth System Science Organization (ESSO) Ministry of Earth Sciences (MoES) India Meteorological Department Long Update for 2014 Southwest Monsoon Rainfall: Model Details & Experimental s ESSO-India Meteorological Department (IMD) issues the operational long range forecasts for the southwest monsoon season (June-September) rainfall over the country as a whole in two stages. The first stage forecast is issued in April based on data up to March and the second stage or update forecast is issued in June based on data up to May. In addition, ESSO-IMD issues forecast for the rainfall over the country as whole during the second half of the monsoon season (August-September) in the end of July and that during the month of September in the end of August. In the second stage, the following operational forecasts are issued: Update for the quantitative and probabilistic forecasts for the Southwest Monsoon season rainfall over the country as a whole issued in April. Quantitative and probabilistic forecasts for the monthly rainfall for July & August over the country as a whole. Quantitative and probabilistic forecasts for the season rainfall for the 4 broad geographical regions of India (NW India, NE India, Central India and South Peninsula). The list of states included in each of these four geographical regions is given below. Northwest India: Jammu and Kashmir, Himachal Pradesh, Punjab, Rajasthan, Haryana, Chandigarh, Delhi, Uttaranchal and Uttar Pradesh. Northeast India: Arunachal Pradesh, Meghalaya, Assam, Nagaland, Manipur, Mizoram, Tripura, Sikkim, West Bengal, Bihar and Jharkhand. Central India: Gujarat State, Madhya Pradesh, Chattisgarh, Maharashtra, Goa and Orissa. South Peninsula: Andhra Pradesh, Karnataka, Tamil Nadu, Kerala, Lakshadweep and Andaman and Nicobar Islands.

4 4 The long period average ( and coefficient of variation of monthly and season rainfall over various regions based on the data are given below: Region LPA (mm) Coefficient of Variation Season (June to September) Rainfall All India Northwest India Central India Northeast India South Peninsula Monthly Rainfall All India (July) All India (August) The Present Operational Long ing System Parameter Ensemble ing System for the Seasonal (June September) Rainfall over the Country as a whole The update forecast for the southwest monsoon season (June-September) rainfall over the country as a whole is issued using a 6-parameter Ensemble ing System. The 6 predictors used are: NE Pacific to NW Atlantic SST Anomaly Gradient (December + January), Southeast equatorial Indian Ocean Sea Surface Temperature (February), East Asia Mean Sea Level Pressure (February + March), Central Pacific (Nino 3.4) Sea Surface Temperature Tendency (March to May - December to February), North Atlantic Mean Sea Level Pressure (May) and Northcentral Pacific 850 zonal wind gradient (May). The 6-parameter ensemble statistical forecasting system was also used to prepare probability forecasts for five pre-defined rainfall categories ing System for the Monthly Rainfall over the Country as a Whole For the quantitative forecasts of monthly rainfall (for the months of July & August) over the country as a whole, separate principal component regression models were used. The models for each month were based on separate set of predictors. The model error of each of these two PCR models is ± 9%. The same models were also used for generating probability forecast for the pre-defined 3 (tercile) categories of monthly rainfall.

5 5 The 3 category probability forecasts for the monthly rainfall over the country as a whole is given below. Rainfall Category July 2.3. ing System for the Seasonal Rainfall over the 4 broad geographical regions of the country For the quantitative forecasts of rainfall during the southwest monsoon season (June to September) over the 4 broad geographical regions, separate principal component regression models were used. The models for each region were based on separate set of predictors. All the four PCR models have average model errors of ± 8% of LPA. The same models were also used for generating probability forecast for the pre-defined 3 (tercile) categories of seasonal rainfall. The 3 category probability forecasts for seasonal rainfall over the four broad geographical regions are given below. All the 3 rainfall categories have equal climatological probabilities (33.33% each). 3. Experimental Dynamical System August (% of (% of Below Normal <94 53 <94 43 Normal Above Normal > > Rainfall NW India Central India South Peninsula Northeast India Category (% of (% of (% of (% of Below Normal <92 71 <94 51 <93 50 <95 33 Normal Above Normal >108 3 > > > Monsoon Mission Experimental Coupled Dynamical Model ing System The Monsoon Mission was recently launched by the ESSO with an objective to improve the monsoon forecasts over the country in short range to long range time scales. The ESSO-Indian Institute of Tropical Meteorology (IITM), Pune is coordinating and working along with different climate research centers from India and abroad on the development of a coupled model for the forecasting Indian summer monsoon rainfall. For this purpose, the state-of-the-art coupled climate model, the Coupled ing System (CFS) developed by the National Centers for Environmental Prediction (NCEP), USA has been implemented at the ESSO-IITM. The latest high resolution research version of the coupled model (CFS Version 2) has been used to generate the experimental update forecast for the 2014 SW Monsoon season rainfall using the April initial conditions. The model has moderate skill.

6 IMD Seasonal Model Since 2004, IMD has been generating experimental dynamical forecast for the southwest monsoon rainfall using the seasonal forecast model (SFM) of the Experimental Climate Prediction Center (ECPC), USA. The global sea surface temperature (SST) forecasts from NCEP coupled forecasting system (CFS) version 2 model was used as boundary forcing for the SFM model. The model showed moderate skill. For generating the forecasts, ten ensemble member forecasts were obtained using the initial conditions corresponding to 00Z from 1 st to 10 th of May. The experimental ensemble forecast based on IMD SFM indicates that the rainfall during the 2014 monsoon season (June to September) averaged over the country as a whole is likely to be 85% ± 4% of long period model average (LPMA). 4. Experimental s from National and International Institutions The experimental forecasts prepared by various national institutes like the Space Applications Centre, Ahmedabad, Centre for Mathematical Modeling and Computer Simulation, Bangalore, Indian Institute of Technology, Bhubaneswar, Indian Institute of Science, Bangalore, Centre for Disaster Mitigation, Jain University, Bangalore, and Center for Development of Advanced Computing, Pune were available. Operational/experimental forecasts prepared by international institutes like the National Centers for Environmental Prediction, USA, International Research Institute for Climate and Society, USA, Meteorological Office, UK, Meteo France, the European Center for Medium Weather s, UK, Japan Meteorological Agency, Japan Agency for Marine-Earth Science and Technology, Asian-Pacific Economic Cooperation (APEC) Climate Centre, Korea and World Meteorological Organization s Lead Centre for Long ing - Multi-Model Ensemble were also available. The forecasts from most of the national and international centers indicate that the 2014 monsoon season (June to September) averaged over the country as a whole is likely to be below normal rainfall. 5. Monsoon So Far This year, the southwest monsoon advanced over the Andaman Sea on 18 th May, 2014, which is 2 days earlier than normal. However, the monsoon set in over Kerala on 6 th June, which is 5 days later than its normal date of onset. As on 9 th June, 2014, the Northern Limit of Monsoon (NLM) passes through 15.0 N/60.0 E, 15.0 N/70.0 E, Karwar, Agumbe, Madikeri, Chennai, 16.0 N/87.0 E, 18.0 N/90.0 E and 21.0 N/92.0 E. The cumulative seasonal rainfall over the country as a whole during the period 1-8 th June is given below: Cumulative Rainfall Regions (1-8 th June) (% of Country as a whole -44 Northwest India -50 Central India -71 South Peninsula -17 North East India -44

Long Range Forecasts of 2015 SW and NE Monsoons and its Verification D. S. Pai Climate Division, IMD, Pune

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