The Southwest Monsoon 2020 started on a positive note with an upbeat of Above Normal rains for the season. In the backdrop of evolving La Nina and neutral IOD during the summer monsoon, the time and spatial distribution of rainfall were expected to be promising. None of the oceanic parameters pointed any spoilsport to tarnish prospects of bountiful rains.
Monsoon made a sound beginning and kept a steady pace with June ending on a surplus note (+18%). However, the core monsoon month July was a dampener which consumed this surplus and ended up with a deficit of 10%. The southwest monsoon halfway through the season was at zero-zero. The month of August saved monsoon 2020 from a potential disaster and ended with a surplus of nearly 4-decade record at +27% and taking the monsoon tally to 110%. Again came to a lean phase during the first week of September and the monthly deficiency rose to 30%. Courtesy, a maiden low-pressure area in the Bay of Bengal, this shortfall is now reduced to 16% and overall monsoon status as above normal with 107% of LPA (long-period average).
La Nina watch is ‘on’ and is likely to become an event during the fall of year or winter season. First time after 30 months (since February 2018) Nino 3.4 has registered a value of -1°C along with other 3 indices also recording -ve values. The probability of La Nina till December is about >= 70% and Neutral at <= 30%. The chance of El Nino is nearly zero.
The Indian Ocean Dipole has generally been below the threshold of -0.4 for the last few weeks and therefore is not contributing towards any surge in the monsoon activity. It is expected to stay neutral/negative during Sep/Oct.
The third oceanic parameter MJO is sailing away from the Indian Ocean in the remaining days of September. The next round is only expected by the middle of October or later and therefore remains inconsequential for the leftover two weeks of September.
The rainfall status of four homogeneous regions displays excess rains over south and central parts of the country. The rainfall over Northwest India and Eastern parts comprising of Bihar, Jharkhand and West Bengal are within normal range with exception of West Uttar Pradesh having deficiency of 34%. The overall monsoon 2020 is likely to end on a positive note with seasonal rains winding up at 107% or above.