Is NEM Heading for Closure over North TN as Bay low heads North?

The Well Marked Low Pressure in Bay of Bengal has been showing signs of consolidation since yesterday as it moved into the open waters over Bay of Bengal.  After making near Westward movement all the while for the past few days since last morning it has started making a NW movement as it started to consolidate.

As we mentioned in our post on 4th December on possible path the disturbance can take the High Pressure Zone over Myanmar will be steering this disturbance on a Northwest Track until Central AP latitude post which it could start moving Northeast if it manages to hold itself under the influence of the Dry Air & Very High Wind Shear prevailing over Central Bay Area.

As explained in the image Cyclones / Depressions are always steered by semi permanent high pressure zones (Ridges) that prevail from time to time. The North Indian Ocean Tropical Cyclones are normally under the influence of the Indo China Ridge or the Indo Arabian Ridge.  Cyclones like Thane were under the influence of the Indo Arabia Ridge which made it dip WSW taking it to Pondicherry.  In the current context the Indo Arabian Ridge is too far west to play any role so it would be the Indo China Ridge to the Northeast of the disturbance that will steer the depression in a NW movement initially and subsequently in a NE recurve depending on survival. Also one needs to also take into account the incoming Upper level Trough as well which are Westerlies in nature and will take disturbances to the East.

But the Key question is what will happen to Northeast Monsoon in particular to North Tamil Nadu.  We are at the stage of the season where rains in North Tamil Nadu slows down.  The ITCZ is already south of Equator and will possibly head further south following the sun deeper into Southern Hemisphere.  With models estimating active disturbances in the coming days over South Indian Ocean it appears difficult for the ITCZ to move back up. In this context it appears we are possibly heading for a Closure of Northeast Monsoon 2017 over North TN.

Numerical Models are also indicating weak rainfall estimates for the next 10 days over North TN.  Places south of Delta and in particular South Tamil Nadu will possibly get another spell of rains possibly around mid December but it appears with no synoptic support ahead after the current Well Marked Low completes its cycle in a few days time.