SOUTHWEST MONSOON SEASON
2009
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India Meteorological Department (IMD) has been adopting a two
stage forecast strategy for South West monsoon rainfall for the past five years
starting with the year 2003. The first long range forecast for the southwest
monsoon season (June-September) rainfall is issued in April using the 8-parameter
models and the forecast update is issued in June based on the 10-parameter
model.
IMD
has now developed new statistical models for forecasting southwest monsoon
rainfall for the country as a whole, which are being introduced this year.
1. A
new 5 parameter statistical forecasting system requires data up to March, will
replace the existing 8-parameter power regression model for the first forecast
in April.
2. A
new 6-parameter statistical forecasting system requiring data up to May will
replace the existing 10 parameter power regression model for the forecast
update in June.
Summary of the long range
forecast of 2009
Southwest Monsoon Season (June
– September) Rainfall
Based upon the newly adopted statistical
forecast system, IMD’s long range forecast for the 2009 south-west monsoon
season (June – September) is that the rainfall for the country as a whole is
likely to be near normal.
Quantitatively, monsoon season rainfall
is likely to be 96% of the long period average with a model error of + or – 5%.
The long period average rainfall over the country as a whole for the period
1941-1990 is 89 cm.
IMD will update the above forecast in
June, 2009 as a part of the second stage forecasts. Separate forecasts for the July rainfall over the country as a
whole and seasonal (June-September) rainfall over the four geographical regions
of
SECOND STAGE FORECASTS for the year 2009 (To be issued in June, 2009)
With
the availability of data up to May, 2009 India Meteorological Department will
prepare the second stage forecasts.
1. Forecast
update for the 2009 southwest monsoon rainfall over the country as a whole
using new 6-parameter ensemble forecast system. The forecasting system has an
error of +/- 4%. The long period average of monsoon (Southwest) averaged over
the country as a whole is 89 cm based on 1941-1990 data with coefficient of
variation of 10%.
IMD’s Long range forecast update for 2009 southwest monsoon
season (June-September) for the country as a whole is likely to be around (to
be issued) of the long period average with a model error of +/- 4%.
2. Forecast
for the rainfall over the country as a whole in the month of July, 2009 based
on 6-parameter model, which has a model error of +/- 9%. The long period
average of monsoon rainfall in the month of July is 293 mm based on 1941-1990
data with a coefficient of variation of 13%.
Rainfall for the country as a whole in
the month of July 2009 likely to be around (to be issued) of long period
average with a model error of +/- 9%.
3. Forecasts
for the southwest monsoon season (June-September) rainfall for the following
four broad geographical regions of
Northwest
India – Jammu & 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, Madhya Pradesh, Chattisgarh,
Maharastra,
Over four broad geographical regions of the country, rainfall
for the 2009 southwest monsoon season is likely to be
All the above four models are with a model error of +/-8%.