2021 saw the highest ever recorded northeast monsoon rainfall in the State, at 1,026.3 mm
2021 saw the highest ever recorded northeast monsoon rainfall in the State, at 1,026.3 mm
After a normal southwest monsoon season, conditions are becoming favourable for the onset of the northeast monsoon, also known as Thulavarsham, over Kerala. Normally, the withdrawal of the southwest monsoon heralds the advent of easterly winds, setting the stage for the entry of northeast monsoon to parts of peninsular Andhra Pradesh and Tamil Nadu.
According to the Indian Meteorological Department (IMD), for announcing the onset of northeast monsoon, the southwest monsoon should withdraw up to the latitude of coastal Andhra Pradesh. Further, there should be fairly widespread rainfall along coastal Andhra Pradesh and easterly winds should be stronger up to 4.5 km above mean sea level. Now, the withdrawal of the southwest monsoon has reached up to 19 degree latitude, near Jalgaon in Maharashtra, as of Saturday and conditions are very likely to become favourable for further withdrawal.
For the 1901-2021 period
A senior IMD scientist told The Hindu that considering the average value of onset of northeast monsoon for the period 1901-2021, the normal onset date is on October 19 with a standard deviation of ± 8 days. Hence, the onset can happen anytime between October 11 to October 27. However, more onset was on October 15 (11 times) followed by October 19 (9 times). The most delayed onset was on November 11 (1915) and the earliest onset was on October 4 (1952, 1966, 1984, and 1999). In 2021, the onset was on October 25.
The current synoptic conditions are favourable for a normal season for Kerala, while 2021 saw the highest ever recorded northeast monsoon rainfall in the history of the State with 1,026.3 mm against the long-period average (LPA) of 491.6 mm. The IMD also forecast that the season (October to December) is most likely to be normal (88-112% of LPA) in Kerala this time.
Six monsoon depressions
The just concluded Edavapathy season (June to September) has seen the State registering normal rainfall, although the number of low-pressure system days was 67 during the season against the normal of 57 days. There were also six monsoon depressions formed during the southwest monsoon season, out of which one intensified into a deep depression in the August 19-23 period. Out of six depressions, four systems formed in August, one in July, and one in September.
