Approaching severe cyclone Ockhi, which is 230 km west-south-west of Mumbai and 390 km south-south-west of Surat, has sent in advance clouds over the North Maharashtra and South Gujarat coasts by noon.

Satellite pictures cloud cover extending from Mumbai to Vasai, Nashik, Daman, Valsad, Navsari, Surat, and further North to Vadodara and just shy of reaching Ahmedabad.

Depression soon in Bay

'Ockhi' will continue to move north-north-east, weaken gradually, and cross the North Maharashtra and South Gujarat coasts as a deep depression (just below cyclone strength) near Surat tonight. Meanwhile, the western disturbance that redirected 'Ockhi' towards the India's West Coast and is responsible for weakening it, is biding its time over Central Pakistan and adjoining East Afghanistan to cross over into North-West India.

It has sent in an offspring cyclonic circulation in advance over Haryana, and it is this circulation that has deepened its influence over the Arabian Sea and by extension the once very severe cyclonic storm Ockhi. The disturbance and the offspring circulation would keep travelling to the East and enter North and North-East India, and in turn spell a cast on a developing depression over the Bay of Bengal next.

A depression is forecast to take shape in the South-East Bay today/tomorrow and is expected to grow as a deep depression, but probably not a cyclone, given the influence of the incoming western disturbance.

La Nina establishes

The depression in the Bay could well be the last of the major sea-based weather systems during this North-East monsoon. A Madden-Julian Oscillation (MJO) wave that triggered 'Ockhi' and other systems have moved out of the Indian Ocean. The moderate to strong pulse of the MJO wave kept the Arabian Sea and the Bay of Bengal spell-bound, and now is moving into the Maritime Continent.

Meanwhile, to the far-east, the Australian Bureau of Meteorology (BoM) has declared that a La Nina (alter ego of El Nino) has established over the Equatorial and East Pacific. But the cooling event would be weak and short-lived, and would fade out after the southern autumn of year 2018 (March to May), just ahead of the onset of the next Indian summer monsoon.

It is generally believed that the performance of the monsoon setting in so soon after a La Nina would largely benefit from the friendly Pacific whose western parts (closer to Asia) should be able to retain some of the warmth. During a La Nina, the warming of the western parts of the Equatorial Pacific helps storm formation and cloud building that in turn improves monsoon sentiments closer home.

After raging as a powerful storm for four days, causing extensive damage to Lakshadweep, taking at least 29 lives in Kerala and leaving many others stranded in the seas, the very severe cyclone 'Ockhi' has started weakening from last night. It is now categorised one notch lower as a severe cyclone, which lay over last night East-Central Arabian Sea about 720 km south-south-west of Surat in South Gujarat and 540 km south-west of Mumbai.

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