A low-pressure area in the Arabian Sea is likely to kick start the Southwest Monsoon season soon. Before the emergence of low pressure, the cyclonic circulation over the area is creating conducive conditions including rainfall over Lakshadweep, Kerala, Coastal Karnataka, and interiors of these states.
Southwest Monsoon onset criteria need fulfillment of a set of environmental conditions over the equatorial region of the Southeast Arabian Sea and rainfall over Lakshadweep, Kerala, and Karnataka.
Rainfall: When 60% of the available 14 stations, viz Minicoy, Amini Devi, Thiruvananthapuram, Punalur, Kollam, Alapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kudulu and Mangalore report rainfall of 2.5mm or more for two consecutive days, the onset over Kerala be declared on the second day provided the following criteria are also in concurrence.
Wind Field: Depth of westerly winds should be up to 600 mb in the specified area (55-80deg E, 0-10deg N). The zonal wind speed should be 15-20kts at 925hpa over a specific area.
OLR: INSAT derived Outgoing Long Wave Radiation (OLR) value should be below 200w/m-2 in the area 5-10degN and 70-75degE.
These conditions are shaping up over the specified area commencing today. Winds are picking up, clouds are thickening and rains becoming fairly widespread over the ocean and drifting coastward. Looks like we have before time onset – a repeat of South Andaman Sea this year.