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It then continued northward movement for some time, and then moved west-
northwestwards across Gangetic West Bengal, Jharkhand, north Chhattisgarh
and west Madhya Pradesh during 17-23 June and weakened gradually. It
weakened into a well marked low pressure area on 23 June over west Madhya
Pradesh. GFS574 has less track error as compared to GFS T382 in all 24 upto
72 hr forecast (Fig 4).
The spatial distributions of MSLP along with specific humidity and wind
at 850 hPa in relation to movement of the system and occurrences of heavy
rainfall are examined. It ushered southwest monsoon over eastern and central
India and caused excess rainfall over these regions. The 16-23 June depression
was responsible for the advance of the monsoon over most parts of the country.
The movement and intensity of this system have been better captured by the
GFS T574 wind and specific humidity (in g/kg) at 850 hPa and MSLP based
on 16 th June 2011 initial condition as compared to GFS T382, as illustrated in
Fig. 5. The movement of this low pressure system has been better forecasted
up to day 3 (valid for 17, 18 and 19 June 2011) by GFS T574 as compared to
GFS T382, as demonstrated in Fig. 5. GFS T574 model showed considerable
skill in predicting the tropical cyclogenesis over the BoB. However, the accuracy
in prediction of location and intensity fluctuates considerably. The positional
error could be further reduced using a tropical cyclone relocation algorithm.
4.2 Heavy Rainfall on 23 June 2011
Under the influence of this low pressure system a heavy to very heavy rainfall
occurred over central India during 20-23 June 2011. The case study selected is
the exceptionally heavy rainfall occasion of 23 June over central India. On 23
June 2011 a heavy rainfall of 34.4 cm was reported at Guna in west Madhya
Pradesh. Figure 6 shows the observed rainfall and 850 hPa wind analysis (top
panel) along with 24, 48 and 72-hour rainfall forecast from GFS T574L64
(middle panel) and GFS T382 (bottom panel) valid for 23 June 2011 over
central India. The spatial correlation coefficient (CC) for GFS T574 is higher
than GFS T382 in all 24, 48 and 72-hour forecast valid for heavy rainfall on 23
June 2011 over central India. The location and magnitude of heavy rainfall on
23 June due to the depression lying over central India is better captured by
GFS T574 as compared to GFS T382. The spatial CC skill suggested that the
GFS T574 model forecasts, in general, are better skillful as compared to T382
in predicting heavy rainfall. Using the GFS T574 operational products, the
location and intensity of heavy rainfall can be predicted up to three days in
advance with an accuracy of spatial error less than 200 km, which can provide
useful guidance for real-time forecasting of heavy rainfall during monsoon
depression over India.
4.3 Monsoon Depression (22-23 September 2011)
The depression during monsoon 2011 formed towards the end of the season
(22-23 September) weakened before moving towards northeast. In association
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