Long Range Forecast Update for the Southwest Monsoon Seasonal Ra…

The second stage forecast  of Southwest monsoon
seasonal rainfall was issued by Indian Meteorological Department(IMD) in New
Delhi today.  IMD has forecast that quantitatively, the monsoon seasonal
rainfall for the country as a whole is likely to be 98% of the Long Period Average
(LPA) with an error of ± 4%.

HIGHLIGHTS

Ø   
Rainfall over the country as a whole for the 2017 southwest
monsoon season (June to September) is most likely to be NORMAL (96% to
104% of long period average (LPA)).

Ø   
Quantitatively, monsoon season rainfall for the country as a
whole is likely to be 98% of the LPA with a model error of ±4%.

Ø   
Region wise, the season rainfall is likely to be
96% of LPA over North-West India, 100% of LPA over Central
India, 99% of LPA over South Peninsula and 96% of LPA
over North-East India all with a model error of ± 8 %.

Ø   
The monthly rainfall over the country as whole is
likely to be 96% of its LPA during July and 99% of LPA
during August both with a model error of ± 9 %. 

India Meteorological Department (IMD) had
issued the first stage operational long range forecasts for the southwest
monsoon season (June-September) 2017 rainfall over the country as a whole on 18^th
April.  In addition to the update of its April assessment, forecasts for the
monthly rainfall for July and August 2017 over the country as a whole, and
seasonal rainfall forecast for the 4 broad geographical regions of India (NW
India, NE India, Central India and South Peninsula) are also presented.

The forecast update for the southwest monsoon
season (June-September) rainfall over the country as a whole was prepared using
a 6-parameter Statistical Ensemble Forecasting System (SEFS). The 6 predictors
used are: NE Pacific to NW Atlantic Sea Surface Temperature (SST) Anomaly
Gradient (December + January), Southeast equatorial Indian Ocean SST (February),
East Asia Mean Sea Level Pressure (February + March), Central Pacific (Nino
3.4) SST tendency (December to February to March to May), North Atlantic Mean
Sea Level Pressure (May) and Northcentral Pacific 850 zonal wind
gradient (May).

Dynamical forecast update generated in real time based on the Monsoon
Mission Coupled Forecasting System (MMCFS) is also presented. The latest
version of the MMCFS (currently operated horizontal resolution of 38km (T382)) is
now implemented for operational use for rigorous performance evaluation on an
experimental model in parallel with the SEFS at the Office of Climate Research
and Services, IMD, Pune upon its transfer from Indian Institute of Tropical
Meteorology, Pune.

Sea Surface Temperature Conditions in the Pacific & Indian Oceans

Since mid-March
2017, warm ENSO neutral conditions are prevailing over the tropical Pacific.
The atmospheric conditions over the Pacific also reflect neutral ENSO
conditions. The latest forecast from MMCFS indicates neutral ENSO conditions
are likely till end of this year. This is in line with the forecasts from some
of the global climate centers. However, outlook from other global climate
centers also indicates about 60% probability of development of weak El Niño conditions
during the second half of this year (2017).    

In addition to
the ENSO conditions over Pacific, other factors such as the Indian Ocean SSTs
have also influence on monsoon rainfall.  At present,
neutral Indian Ocean Dipole (IOD) conditions are prevailing over Indian Ocean.
The latest forecast from the MMCFS indicates weak positive IOD conditions are likely to develop during the
monsoon season.

The second Stage Forecasts
of Southwest Monsoon Seasonal Rainfall for 2017

i)                   
Monsoon Mission Coupled Forecasting System (MMCFS)

The latest experimental forecast based on the MMCFS
suggest that the monsoon rainfall during the 2017 monsoon season (June to
September) averaged over the country as a whole is likely to be 100% ± 5% of LPA.

ii)         Seasonal (June-September) Rainfall over the country as a
whole

Quantitatively,
the season rainfall for the country as a whole is likely to be 98% of the long
period average (LPA) with a model error of ±4%. The LPA rainfall over the
country as a whole for the period 1951-2000 is 89 cm.  

The 5 category probability forecasts for the Season (June
to September) rainfall over the country as a whole is given below.

It is to
mention that region wise forecast assessment based on MMCFS was nearly in line
with the forecast from the statistical models. 

iii)        Season (June-September) Rainfall over Broad Geographical
Regions

The season rainfall is likely to be 96% of LPA over
North-West India, 100% of LPA over Central India, 99% of LPA over South
Peninsula, and 96% of LPA over North-East India all with a model error of ± 8
%.

iv)        Monthly (July & August)
Rainfall over the country as a whole

The rainfall
over the country as a whole is likely to be 96% of its LPA during July and 99%
of LPA during August both with a model error of ± 9 %.

——–

RDS/nb