North Indian Ocean has two distinct cyclone seasons. The first characterised as Pre Monsoon during April and May which at times spills over into June. The 2nd characterised at Post Monsoon which coincides with Northeast Monsoon. IMD which is the RSMC for North Indian Ocean basin has a an exhaustive FAQ section on Tropical Cyclone. Southwest Monsoon season sees very less cyclone activity due to the presence of Vertical Wind shear. As we all know Southwest Monsoon is driven by strong lower level Westerlies. But it also has a key upper tropospheric Easterly component as well. This results in high vertical wind shear preventing formation of cyclones.
Time to time we have had some exceptions though cyclones during Southwest Monsoon. One such instance was Cyclone Biparjoy standing out by staying nearly two weeks during Onset os SWM 2023. Another Cyclone Komen which formed during late July over Bay of Bengal and made landfall on 30th July over the Bangladesh Coast. The second fortnight of September though off late has seen an increase in tropical cyclones possibly driven by transition dynamics. Special mention needs to be made to Gulab and Shaheen during the year 2021. After taking genesis in Bay of Bengal intensifying into Gulab the disturbance resurfaced in Arabian Sea as Shaheen. Gulab made landfall over Andhra Pradesh while Shaheen made landfall over Oman.
The current Deep Depression will be only the 1st instance of a cyclone in Arabian Sea during August since 1981. It will also be only the 4th instance of a cyclone during August in Arabian Sea since 1891. Interestingly 1976 August saw a depression from Odisha move across Central India resurface as a Cyclone over the Arabian Sea. Not only did it resurface as a cyclone but also made a loop over North Arabian Sea. In a way the near stationary movement of the current Deep Depression has parallels to the 1976 event. When the deep depression intensifies briefly into a Cyclonic storm it would be named Asna a name given by Pakistan. Ironically Gulab in 2021 was also given by Pakistan which resurfaced in Arabian Sea as Shaheen.
The Low Pressure Area that formed over Central Bay yesterday is likely to become well marked today. As it strengthens it is likely to move towards Odisha / North AP coast becoming a depression in the process. Over the next few days this depression will drive the monsoon dynamics as it moves across Central India. The to be Cyclone over Arabian sea will move further west towards Arabian Peninsula. In what may be a concern sub seasonal models indicate Peninsular India may not see a monsoon surge. This is certainly a worry despite the presence of a Low over Central Bay. Possibly the presence of a cyclone over North Arabian sea may be playing a role in this though it is debatable.
In another worry there is a high chance parts of Gujarat, particularly around Vadodara, might see another instance of very heavy rains later next week. This could potentially lead to one more instance of flooding water logging as well. For the next couple of days AP & TS states though need to be on alert for possible very heavy rains as the circulation moves closer to the coast. Godavari basin may once again see heavy inflows due to rains in the catchment areas.
Closer home today possibly represents one final chance for thunderstorms over North TN due to favorable wind convergence. As the LPA deepens into a depression and gets closer to the coast westerlies will strengthen leading to reduced chance for thunderstorms. While most parts of TN may be under cloudy skies today some thunderstorms could develop later in the evening around North TN / South AP which could drift towards the coast.