The countdown to the onset of Monsoon in Kerala has started. Monsoon clouds are approaching the West Coast of India, making conditions favourable for the onset of Southwest Monsoon.
However, we should keep in mind that the onset of Monsoon is a complex phenomenon involving research for weeks or even months. Before declaring the onset of Monsoon in Kerala we should certain guidelines and in this story we will discuss these criteria.
a. Rainfall
As we approach the onset date, 60% of the 14 stations across Kerala and coastal Karnataka should record 2.5 mm rainfall or more for two consecutive days. These stations are Minicoy, Amini, Kollam, Thiruvananthapuram, Kannur, Punalur, Alappuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kudlu and Mangalore.
b. Wind Field and Wind Speed
The depth of the southwesterly winds should be up to 600 hPa or 12000 ft high, from the equator to 10°N, between 55°E and 80°E. The zonal wind speed over the area bounded by Latitude 5-10°N and Longitude 70-80°E should be around 25 to 35 kmph in the lower levels.
c. Outgoing Longwave Radiation (OLR)
The OLR value should be less than 200 wm-2 in the box confined by Latitude 5-10°N and Longitude 70-75°E.
Northern Limit of Monsoon
At present, the Northern Limit of Monsoon (NLM) passes through 6.0°N/60.0°E, 6.0°N/70.0°E, 7.0°N/80.0°E, 10.0°N/86.0°E, 13.0°N/89.0°E and 18.0°N/95.0°E
The NLM was stagnant over Hambantota in Sri Lanka for over a week but, now it has reached Colombo.
Click here to know, What is Northern Limit of Monsoon?
Advancement of Monsoon is based on various pre-requisites, other than rainfall. In the next two days, most of the criteria will be fulfilled except for the wind field and speed. Analysing the weather models, we can say that there will be a weak onset of Monsoon in Kerala. In other words, all the parameters for the onset of Monsoon will not be fulfilled.
After the onset of Monsoon, its further advancement takes place based on many drivers including vortex in the Andaman Sea and Bay of Bengal, low pressure areas, activity of the Monsoon trough and Western Disturbances in North India.
image credit- India TV
