Multi-model Ensemble Based Extended Range Forecast of Tropical Cyclogenesis over the North Indian Ocean - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 204

3.2 MME Outlook of Cyclonic Storm during 2011
Post-monsoon Season
The low level relative vorticity, low level convergence and the rainfall forecasts
based on multi-model extended range forecasts are analysed to study the genesis
of TCs.
(i) Depression over the Bay of Bengal (19-20 October, 2011)
The depression over Bay of Bengal which crossed Myanmar coast on 20 th
October, 2011 is very well captured in the weekly MME forecast mean wind
valid for the period 17-23 October, 2011 based on initial condition of 13 October
(days 5-11 forecast) (Fig. 2a) and based on initial condition of 06 th October
(days 12-18 forecast) (Fig. 2b). There is fairly good indication of closed cyclonic
circulation in the MME forecast valid for days 5-11 and days 12-18. Thus,
even two weeks in advance the formation and likely movement was well
anticipated in the MME forecast. The forecast rainfall anomaly based on 13
Oct and 06 Oct initial conditions also indicated active convection leading to
rainfall over the Bay of Bengal in the rainfall anomaly (Fig. 2c-2d), which
indicated rainfall over the Myanmar coast consistent with the location of
formation of the system.
(ii) Two Depressions and One TC over the Arabian Sea
After the depression that crossed Myanmar coast on 20 October, the post-
monsoon season of 2011 did not get any system over the Bay of Bengal, whereas,
the Arabian Sea was very active with two depressions and one TC formed as
shown in Fig. 1. Two systems formed in the first fortnight of November of
which one is the TC “Keila” formed during 29 Oct to 4 November and the
other depression formed over the Arabian Sea during 6-10 November. The 18
days forecast based on the initial condition of 27 October, 2011 valid till 13
November clearly indicated very active Arabian Sea and no indication of genesis
of any system over the Bay of Bengal till 13 November, 2011. The MME
forecast weekly mean wind and weekly anomaly wind based on 27 October
initial condition and valid for days 5-11 (31 Oct-6 November) and days 12-18
(November 7-13) indicated the formation of systems over the Arabian Sea as
seen in the mean 850 hPa wind (Fig. 3a-d). The mean forecast wind and wind
anomaly clearly indicated presence of cyclonic circulation over the Arabian
Sea (Fig. 3a-b), whereas, anomalous anticyclonic circulation prevailed over
the Bay of Bengal during this period (Fig. 3c-d).
The days 5-11 forecast mean vorticity during the period also indicated
cyclonic vorticity over the Arabian Sea during the period 31 Oct-06 November
(Fig. 4a), with the centre of maximum migrated further northwestward during
the period 07-13 November, 2011 during the period of days 12-18 forecast as
seen in Fig. 4b. The MME forecast weekly mean and weekly anomaly rainfall
valid for days 5-11 (31 Oct-6 November) and days 12-18 (November 7-13)
indicated the formation of systems over the Arabian Sea as seen in the mean