Southwest Monsoon Onset Soon Over Kerala: Mandatory Conditions To Be Fulfilled
May 20, 2025, 4:38 PM | Skymet Weather Team
The southwest monsoon has advanced over the Andaman Sea, parts of Southeast and South Bay of Bengal (BoB), equatorial regions of the Arabian Sea next to the Maldives and Comorin area, and most parts of Sri Lanka. Conditions are favorable for its further advance over more parts of South and Central BoB, the Southeast Arabian Sea, the whole of Sri Lanka, and coastal parts of North Myanmar and Bangladesh. For onset over mainland India (Kerala), there are a set of conditions to be fulfilled, mandatorily, for a period of at least two consecutive days.
Rainfall: If after 10th May, 60% of the available 14 stations, viz., Minicoy, Amini Divi, Thiruvananthapuram, Punalur, Kollam, Alappuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kudulu, and Mangalore, report rainfall of 2.5mm or more for two consecutive days, the onset over Kerala will be declared on the 2nd day, provided other parameters are also fulfilled.
Wind Field: Depth of westerly winds should be maintained up to 12,000 feet in height in the box from the equator to latitude 10°N and longitude 55°-80°E. The zonal wind speed over the area bounded by 5°-10°N and longitude 70°-80°E should be of the order of 15-20 knots at 3,000 feet height.
Outgoing Long Wave Radiation (OLR): The INSAT-derived OLR value should be below 200 watts/sq. mtr. in the box confined by latitude 5°-10°N and latitude 70°-75°E.
Out of these, even as of today, all the requisite conditions are met with, except the OLR. However, because of a likely depression coming up over the east-central Arabian Sea, off the Konkan & Goa coast, the rainfall will reduce over Kerala for the next three days.
It will start raining again from 23rd May onwards. By then, the OLR values will also fall in place. The southwest monsoon may possibly be announced anytime between 24th and 26th May 2025. If so, this will become the earliest arrival of the monsoon since 2009.
