The Southwest Monsoon (SWM) may likely advance into the South Andaman Sea, Nicobar Islands and some parts of southeast Bay of Bengal by May 13, 2025, according to the latest update from the India Meteorological Department (IMD) on May 11.
On May 10, the weather agency predicted that the SWM may onset over Kerala on May 27, four days earlier than the normal onset date of June 1. On April 15, the IMD had stated that SWM in 2025 is likely to bring above normal to excess rainfall.
The monsoon winds may be pulled and aided by the formation of a low-pressure area that may or may not intensify into a tropical cyclone. The low-pressure system may influence the SWM in its initial phases in the Bay of Bengal but not much later during the onset over Kerala.
Both the Global Forecasting System (GFS) of the United States and the European Centre for Medium range Weather Forecasts (ECMWF) model show the formation of a low pressure area in the Bay of Bengal but not much intensification.
“The cyclone is likely to form but it’s too early for affecting the onset, I think. It may pull the trough to the Andaman Sea a little earlier depending on its intensity,” Raghu Murtugudde, professor of climate studies at Indian Institute of Technology, Bombay and emeritus professor at the University of Maryland told Down To Earth.
The months of April and May have been replete with thunderstorm activity over many regions of India, which is still continuing. The thunderstorms have been accompanied by hail and rainfall. This has meant a respite from the ongoing heat wave activity in many parts of the country and cooling of the land to some extent.
The heightened activity of thunderstorms has been because of continuing activity from western disturbances in April and May and the formation of multiple upper air cyclonic circulations and associated troughs, which are elongated low pressure regions. A western disturbance was active in the middle troposphere as of May 11, according to IMD.
According to IMD’s press release from May 11, the thunderstorms are going to affect different parts of India till at least May 15.
Usually, the heating of the land in April and May is necessary for the timely onset and propagation of the SWM but the current thunderstorms may not interfere with the monsoon onset.
“The thunderstorms are too early and shouldn’t tinker too much with the monsoon onset”, said Murtugudde.
On the other hand, “if they provide enough soil moisture then cyclone may use the soil moisture to stay more active on land depending on its path. When cyclones cross the peninsula, that’s what happens but that’s relatively rare,” concluded Murtugudde.
Meanwhile, the IMD predicted on May 11 that the SWM “is likely to further advance over some parts of south Arabian Sea, Maldives & Comorin area; some more parts of South Bay of Bengal, entire Andaman & Nicobar Islands and Andaman Sea; and some parts of central Bay of Bengal during subsequent 4-5 days”.