***** Refer "Whats to happen Now" below
BB-11 has defied and challenged ALL International weather models (not comparing Vagaries with them) and taken its own course, first North and now West.
Positioned at 13.6N AND 88.7E, West of Chennai.
It is necessary to understand the forecasts and estimates given by various models. No model goes on guess work. There are certain presumptions and assumptions, with reasoning behind each forecast. And, forecasts may be diametrically opposite to each other.
a) NOGAP as on today (Friday) forecasts a W/NW movement towards TN/AP coast, and become a depression. (http://ow.ly/i/18830)
Vagaries also had subscribed to this view from the initial stage. The reason behind this forecast by all models: TD-25 was to send in a pulse, and form a low/depression (BB-12) in the Andaman region by the 16th and influence the initial movements of BB-11. The advent of BB-12 would have curved the trough in which BB-11 is nestled towards the West. And, the 200 hpa jet streams were seen flowing towards the NW in the Southern Bay.
BB-11 would have moved into TN as a depression.Though some models like IMD GFS and FNMOC had mentioned this track, they changed it as they observed the change in the jet streams and pressure "play" in the Bay.
b) Some models predicted, FNMOC, UKM, COLA a North/North-East track, presuming the ridge in the Bay will prevail. Ridge ? Yes, instead of a trough. This ridge in our seas was dependant on the High in the Phillipines region.TD-25 was nestled between these 2 Highs.
What's actually happening now ? The extreme East Phillipines ridge has weakend, the TD-25 is fizzling out, the parent pulse itself is fading.
BB-11, is now moving West. But, the low is stagnent in strength, and seems to be getting elongated. Now, this elongation was expected, and BB-12 was to get more strengthened by merging in this "big" low. But where is BB-12 ?
*****Ok, leave all this, what's to happen now? What can happen if BB-12 does not come ? Well, BB-11 will be on its own, and merge into the larger region of 1008 mb. Till survival, NW movemnet not ruled out for the next 18-24 hrs. That is, it will elongate to form a huge Low region of 1008 mb(weaken) in the Bay. Showers will push into Oriissa/West Bengal coast from 18th/19th.
Showers also possible in coastal and interior TN.
A pre-mature Low in the Gulf of Munnar region may get a lease of life.
On Friday, N-1 moves into Pakistan and will be resisted by an anti-cyclone over Central India. Next 2 days, Northern regions of Pakistan, Northern Indian States of Kashmir and HP gets snow in higher and middle ranges of Utteranchal get rains.
Cloudy weather for Punjab and Northern Haryana with light rains in Northern plain regions.