Expected Low Pressure in Bay – A Reality Check

With a lot of people asking about the upcoming Low Pressure in Bay we think it is prudent to explain the current conditions and the context of how the situation is evolving and why we need to be little more patient to allow things to evolve.

Northeast Monsoon Update: The Upper Air Cyclonic Circulation currently off Andaman Islands is expected to influence a Low Pressure in the next 24 – 48 hours.  Until the low pressure forms it is going to be fairly dry weather for most parts of Tamil Nadu.

So what happens to the expected heavy rainfall over coastal Tamil Nadu?  While it is quite clear the Low Pressure Area in Bay is expected to form over the next couple of days there is still a lot of inconsistency in the tracks and time frame.  As things stand while from today till the 28th November there is some sync between the two major models ECMWF & GFS. At this point the low pressure area is roughly ESE of Sri Lanka with possibly impact on Coastal South TN / Delta regions

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From here on there is some divergence in the models both in terms of the potential circulation developing & track.  The reason for this divergence is on account of GFS expecting a second vortex closer to Andaman Islands becoming the dominant circulation from 29th onwards and then moving towards closer to the Indian Coast.

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As one can see above there is a huge divergence in the track and time frame which is possibly on account of both the models picking up different circulations to evolve.  This divergence in the time frame and track is also showing up in the precipitation estimates between the models.  ECMWF expects the heaviest rainfall for North Coastal TN (incl. Chennai) on 30th November while GFS expects the rains to happen mostly over the sea on that day.

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In this context we feel it would be prudent to be patient and allow things to evolve rather than panic.

At no point are we discounting the probability of heavy rainfall over Coastal Tamil Nadu but the impact areas are likely to change and the dates as well depending on how and where this low pressure forms.  

Chennai Weather Forecast: Early morning rains in a few areas which could ease off by about 8 / 9 AM, fairly clear weather day subsequently.  Day time temperature expected to be around 31°C