Skymet weather

Hasty Monsoon Declaration, Onset Criteria Blatantly Set Aside

May 30, 2022 1:37 PM |
Rain in Kerala

Onset of southwest monsoon was declared yesterday  by the National Weather Agency. It also stated that monsoon has arrived 3 days before the scheduled date of 01stJune over Kerala. Earlier, Skymet had predicted the arrival on 26thMay and  IMD on 27th May.  In the last 3 years, the monsoon arrived on 08thJune, 01stJune and 03rd June in 2019, 2020 and 2021 respectively.

Onset of monsoon has specified objective criteria comprising of rainfall, winds and outgoing long wave radiations (OLR). If after 10thMay, 60% of the available 14stations, viz Minicoy, Amini Divi, Trivandrum, Punalur, Kollam, Alappuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kudulu, and Mangalore report rainfall of 2.5mm or more for 2 consecutive days, the onset over Kerala be declared on the 2nd day, provided the winds and OLR criteria also remains in concurrence.

 Wind Field : Depth of westerly winds should be maintained up to 600 hPa, in the box 0°-10°N and 55°-85°E. The zonal wind speed over the area bounded by 5°-10°N and 70°-80°E should be of the order of 15-20 knots at 925 hPa.

OLR:  INSAT derived OLR value should be below 200 Watt/ sq. meter in the box confined by 5°-10°N and 70°-75°E.

24 Hr Rainfall (mm) –  Monsoon Stations

Winds and OLR got aligned with the requirement of onset for the last 2days.  However, the most important and visible manifestation of rainfall fell short on 28th and 30th May.     Onset conditions were fulfilled only for one day, 29thMay. Day prior (28th May) and day later (30thMay), merely </= 40% of the designated stations met the rainfall criteria. 

Declaring monsoon based on single day observations amounts to gross violation of standards, never attempted in the past.  Any repute scientific body can ill afford to bend rules and criteria, just to prove the forecast right.  Such a step, if taken knowingly, becomes highly objectionable and if otherwise, amounts to illusion of knowledge.   

Monsoon does not seem to be kicking up soon over Kerala and Peninsular India.  Today, 7 out of the 14 earmarked stations have recorded NIL rainfall and 2 more locations have registered less than 1mm.  Most locations with fair amount of sunshine fail to give the monsoon feel. At best, Northeast India is well with in norms for announcing southwest monsoon. Most areas of Tamil Nadu, Karnataka, Kerala and Rayalaseema will have to wait to catch up with proper monsoon stream.      ...

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