Peninsular India is one of the toughest places to follow weather. As a region surrounded by water oceans play a major role in how weather events happen in our part of the world. Additionally mid latitude factors also influence tropical events. Many a times we have seen tropical cyclones come under the influence of westerly troughs during NEM. This complex nature makes it a grave yard for global numerical weather models. Often we have not only seen seasonal forecasts go wrong but even operational models in short term completely miss events.
Northeast Monsoon this year has been particularly challenging to follow. What started off with a bang quickly tapered off during November as West Pacific decided to show itself up. 4 simultaneous storms meant NEM had to gasp for breath during peak season. Since 1951 for the first time West Pacific saw 4 named storms during November. An unfavourable MJO transit pretty much brought a poor period of rains during 1st fortnight of November.
The mid November LPA and the subsequent Easterlies did turn the table for Delta and South TN. After being deficit for pretty much entire 1st half of Monsoon delta districts like Nagapattinam moved into excess. Even districts like Thoothukudi managed to cut deficit by nearly half during this period. The biggest losers though continue to be North Coastal TN. Kanchipuram district now has -39% deficit making it the worst performing district as on date.
Despite the arrival of MJO and potential development of an LPA the anxiety of another poor rainfall event is overpowering the thoughts of most weather watchers. Numerical models continue to diverge even within the short period of 48 hours both in terms of intensity and path. It becomes essential in this context to take one day at a time. Compare the real time events with forecasts and make course corrections as things evolve.
Satellite image indicates the cyclonic circulation over Andaman Sea continues to remain disorganised. The presence of another circulation over South of Equator is a reason for the difficulty in consolidation. This could also mean a delay in consolidation and potential impact on the intensity as well. This is the first unknown of this LPA. The model that picks up this phase well would eventually get the overall dynamics right. Currently most European models tend to lean towards a weaker disturbance. The two North American models, GFS and GEM, seem to lean towards a stronger system. Except for GFS all the other models take a more WNW path towards Sri Lanka.
This brings us to the second unknown in the overall dynamics. How would Sri Lankan land interaction impact the overall path and intensity. As far as GFS goes there is no interaction so it has opted to intensity this disturbance into a strong cyclone. GEM strangely continues to intensity the disturbance despite Sri Lankan land interaction. There is a tighter agreement once again among the European models about keeping the disturbance weaker as it gets close to Sri Lanka. In 2020 we had Cyclone Burevi that brushed North Sri Lanka as a cyclone. Going by European models the overall path may be very similar to Cyclone Burevi. The intensity though is unlikely to be a Cyclonic Storm. But it will make sense to wait and watch over the next couple of days though.
The path will also play an important role in the rainfall impact for Coastal TN. Delta is ideally placed considering it may get rains as long as the path brings the LPA towards Sri Lanka. Whether south of Sri Lanka or North of Sri Lanka delta districts may receive good rains. Only if the path goes as per GFS estimates, which potentially brings a westerly trough influence, would delta miss out on rains. As far as North TN goes a path bringing the LPA / Depression to the NE of Sri Lanka would benefit the most. The caveat here is the 3rd unknown. Westerly trough influence which is picked up models like GFS and ECMWF ML.
Considering the westerly trough influence is expected during the 2nd half of next week it make sense to keep this on low priority. The events during the first two phases of unknowns is likely to decide the eventual path and impact zones rather than the 3rd unknown. One day at a time is the only way to look at this disturbance as things stand. The only knowns as of now is arrival of Easterlies may bring light to moderate rains over coastal areas starting from later tonight / early tomorrow morning. Rest all as things evolve.