LONG RANGE FORECAST SW MONSOON PRESENT STATUS 2014

LONG RANGE FORECAST SW MONSOON ESSO (Earth System Science Organization) MoES ( Ministry of Earth Sciences) IMD 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.

LONG RANGE FORECAST SW MONSOON 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 Forecasting System.

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).

OVER THE COUNTRY AS A WHOLE 6-PARAMETER ENSEMBLE FORECASTING SYSTEM FOR THE SEASONAL (JUNE – SEPTEMBER) RAINFALL OVER THE COUNTRY AS A WHOLE 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) Northcentral Pacific 850 zonal wind gradient (May).

THE 6-PARAMETER ENSEMBLE STATISTICAL FORECASTING SYSTEM ALSO USED TO PREPARE PROBABILITY FORECASTS FOR FIVE PRE-DEFINED RAINFALL CATEGORIES. Forecasting System for the Monthly Rainfall over the Country as a Whole . (a) Separate principal component regression(PCR) models were used.. Models for each month were based on separate set of predictors. (b) The model error of each of these two PCR models is ± 9%. (c) Used for generating probability forecast for the pre-defined 3 (tercile) categories of monthly rainfall.

(a) All the four PCR models have average model errors of ± 8% of LPA 2. Forecasting System for the Seasonal Rainfall over the 4 broad geographical regions of the country (a) All the four PCR models have average model errors of ± 8% of LPA (b) Used for generating probability forecast for the pre-defined 3 (tercile) categories of seasonal rainfall. (c) All the 3 rainfall categories have equal climatological probabilities (33.33% each).

EXPERIMENTAL DYNAMICAL FORECAST SYSTEM 1. Monsoon Mission Experimental Coupled Dynamical Model Forecasting System : (a) ESSO-Indian Institute of Tropical Meteorology (IITM), Pune coordination. Development of a coupled model for the forecasting Indian summer monsoon rainfall. (b) Coupled Forecasting System (CFS) developed by the National Centres' for Environmental Prediction (NCEP), USA has been implemented (c) The model has moderate skill.

EXPERIMENTAL DYNAMICAL FORECAST SYSTEM 2. IMD Seasonal Forecast Model :- (a) 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. (b) For generating the forecasts, ten ensemble member forecasts were obtained using the initial conditions corresponding to 00Z from 1st to 10th of May. (c) The model has moderate skill. (d) Rainfall is likely to be 85% ± 4% of long period model average (LPMA).

EXPERIMENTAL FORECASTS 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 Range Weather Forecasts, 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 Range Forecasting - Multi-Model Ensemble were also available.

REGIONS FOR MONITORING ENSO SEA SURFACE TEMPERATURE ARE MONITORED IN FOUR REGIONS ALONG THE EQUATOR : NINO 1 (80°-90° W AND 5°-10°S) NINO 2 (80°-90° W AND 0°-5°S) NINO 3 (90°-150° W AND 5°N-5°S) NINO 4 (150°W-160°E AND 5°N-5°S) NEW REGION NINO 3.4 (120°-150°W AND 5°N-5°S) IS NOW USED AS IT CORRELATES BETTER WITH THE SOUTHERN OSCILLATION INDEX AND IS THE PREFERRED REGION TO MONITOR SEA SURFACE TEMPERATURE

EFFECTS OF EL NINO HIGHER SEA LEVEL AND SST TOWARDS EAST PACIFIC LOWER SEALEVEL AND SST TOWARDS WEST PACIFIC