With GAMEDE still evolving near longitude 75° E, another low pressure appeared near 87° E and eventually developed into a tropical depression by 21 February night. It had a broad but poorly defined clockwise circulation flaring west of the low level centre. From thereon till 22 February/ 16hrs00, the system maintained the same intensity (T number 2.0) with however a slightly better organisation of the low level circulation which nevertheless remained exposed east of the fluctuating deep convection. This was mainly due to an upper level moderate east-north-easterly shear prevailing within the environment in which the system was embedded. This easterly wind shear persisted but on the other side the upper level divergence improved, which led to a better organisation of the low level circulation. This led to a further intensification of the system which reached a T number 2.5 by early morning of 23 February. It was named HUMBA at 09hrs30 (near 12.8° S and 82.1° E) on the same day. Having maintained a T number of 2.5 since early morning, the moderate tropical storm HUMBA attained a T number of 3.0 in the afternoon. (Refer trajectory). HUMBA was evolving along the north-western periphery of an anticyclone and tracked towards the south-west, intensifying rather rapidly at the same time to reach severe tropical storm (STS), T number 3.5, at 22hrs00. From 23/22hrs00 to 24/04hrs00, it had maintained a general south-westerly movement with a tendency to intensify further. It reached a T number 4.0+ on 24 night tracking in a more southerly direction after 04hrs00. HUMBA was still located along the north-western edge of the mid level ridge east of it and the environment had a good poleward upper level outflow. This favoured a more southerly track and further intensification when it reached a tropical cyclone intensity (T number 4.5) near 20.5° S and 77.2° E on 25 February at 22hrs00. The general southerly track was maintained where tropical cyclone (TC) HUMBA was eventually expected to enter an environment with increasing vertical wind shear. As TC HUMBA tracked further southwards, its convective activity started to get disorganised under a northerly vertical wind shear. Most of the convective activity shifted to the south of the low level clockwise circulation. On the 26 February at 04hrs00, TC HUMBA weakened into a severe tropical storm (T number 3.5). By 27 February at 10hrs00, HUMBA was already an extra-tropical depression still tracking south onto a cooler environment.
Posted on: Tue, 15 Oct 2013 17:14:26 +0000
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