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Normal Rainfall Predicted for Southwest Monsoon 2018

India Meteorological Department (IMD) is issuing the forecast for the southwest monsoon seasonal rainfall (June to September) 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 June. IMD is using state-of-the-art Statistical Ensemble Forecasting system (SEFS) which 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 forecasts. Latest version of the high resolution (horizontal resolution of approximately 38 km (T382) Monsoon Mission CFS (MMCFS) was implemented in January 2017.

For April forecast, 5 predictors are used which require data up to March:

S.No Predictor Period
1. 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

Forecast based on the Monsoon Mission Coupled Forecasting System (MMCFS):

MMCFS suggests that monsoon rainfall during the 2018 monsoon season (June to September) averaged over the country as a whole is likely to be 99 per cent ± 5 per cent of the Long Period Average (LPA).

Forecast Based on the Operational Statistical Ensemble Forecasting System (SEFS):

Monsoon will be normal and rainfall is likely to be 97 per cent of the Long Period Average (LPA) with a model error of ± 5 per cent.

(Normal Monsoon Rainfall over the country as a whole is 89 cm).

 Forecasts Probability over the country as a whole:

Category

 

Rainfall Range

(% of LPA)

 

Forecast

Probability (%)

 

Climatological

Probability (%)

 

Deficient < 90 14 16
Normal 96 -104 30 17
Below Normal 90 – 96 42 33
Above Normal 104 -110 12 16
Excess > 110 02 17

In addition of updated forecast in early June, 2018, separate forecasts will be made for rainfall in the months of July and August over the country as a whole and seasonal (June-September) rainfall over the four broad homogeneous regions of India.

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

The latest forecasts from MMCFS & other global models indicate conditions over the Pacific will turn to neutral ENSO conditions before the beginning of the monsoon season.

The latest forecasts from the MMCFS and global models indicate weak negative Indian Ocean Dipole (IOD) conditions may develop during the middle of the monsoon season.

With Inputs from IMD.

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