Friday, 11 May 2018

IMD forecasts monsoon’s arrival by May 25

11/5/2018

PUNE: The India Meteorological Department's (IMD) forecast models indicate an early onset of the monsoon this year. The weather bureau has already announced a normal monsoon.

Though the official onset forecast by IMD is expected on Saturday, models run by the met department show the monsoon’s onset over Kerala around May 25. The normal date is around June 1. This could be the earliest monsoon arrival over Kerala in the last seven years.

Forecast models show that various onset criteria are likely to be fulfilled around that time, including a change in the wind direction and good rainfall over the southern tip of the country. Monsoon circulation generally starts from the second week of May with the wind direction gradually changing to westerly in the lower levels of the troposphere.

When the westerly depth goes up to 5 km, it establishes the monsoon circulation and this is when the onset of monsoon occurs. After setting in over Kerala, the southwest monsoon advances northwards, usually in surges, and covers the entire country by July 15. Weather models show that changes in the wind circulation pattern will become prominent between May 18 and May 24 over the Arabian Sea. The wind flow is expected to become more westerly in the period between May 25 and 31 over southeast Arabian Sea.

Models also show that a good amount of rainfall is likely to occur in the Arabian Sea and the adjoining south peninsula not only in the May 11 to May 17 period but also in the May 18 to May 24 time frame. The latter period is likely to experience above normal rainfall activity over the southeast Arabian Sea, adjoining Kerala and south peninsula region, enhancing the possibility of an early onset of monsoon over the southern tip of India. Sources said that required conditions for monsoon arrival like the establishment of low-level jet around May 25, westerly wind prevailing up to 700 millibars, good rainfall over southern tip of India - all seem to indicate early arrival over Kerala.

J R Kulkarni, retired meteorologist and All India Internet Weather Radio Station founder, said the time of monsoon onset and the amount of rainfall received during a season are not connected. “There have been instances in the past when the onset was late, but the seasonal rainfall was above normal. The monsoon’s timely arrival and the onset is important for the kharif season in the peninsular states of Karnataka and Maharashtra,” Kulkarni said.

Once it hits Kerala, farmers Maharashtra and Karnataka can gauge that it will hit their states in seven to eight days. The monsoon normally arrives in Maharashtra around June 7.

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