Geoscience Reference
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3. Synoptic Situations of Aila and Gonu
The synoptic situations of the above mentioned tropical cyclones Aila over
Bay of Bengal and Gonu over Arabian Sea are presented in this section.
3.1 Case 1 (Aila)
With the influence of the southwest monsoon over Andaman Sea and adjoining
south Bay of Bengal on 20 May 2009, the southerly surge over the region
increased. It resulted in increase in the horizontal pressure gradient and the
north-south wind gradient over the region. Hence the lower level horizontal
convergence and relative vorticity increased gradually over the southeast Bay
of Bengal. It led to the development of the upper air cyclonic circulation
extending up to mid-tropospheric level on 21 May over the southeast Bay of
Bengal and associated convective cloud clusters persisted over the region. Under
the influence of the cyclonic circulation, a low pressure area formed over the
southeast Bay of Bengal on 22 May morning which concentrated into a
depression and lay centered at 1130 hours 23 May near Lat. 16.5ºN/Long 88.0ºE,
about 600 kms south of Sagar Island. Figure 1 depicts the satellite imageries of
the Aila cyclone at different stages of intensification. Figure 1(a) is during the
cyclonic stage (CS) valid at 12 UTC 24 May 2009, 1(b) represents the imagery
at severe cyclonic stage (SCS) valid at 06 UTC 25 May 2009 and 1(c) is the
image during landfall of the storm valid at 08 UTC 25 May 2009.
3.2 Case 2 (Gonu)
A low pressure area developed over east-central Arabian Sea on 31 May 2007.
It concentrated into a depression over the same area and then into a cyclonic
storm Gonu at 12 UTC of 1 June 2007. Thereafter, it moved in a north-
northwesterly direction and intensified into a severe cyclonic storm at 03 UTC
of 3 June 2007. It intensified into a very severe cyclonic storm at 18 UTC of 3
Fig. 1: Satellite imagery of tropical cyclone Aila valid at (a) 12 UTC 24 May 2009, the
cyclonic stage; (b) 06 UTC 25 May 2009, the severe cyclonic stage and (c) 08 UTC 25
May 2009, the landfall time.
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