Cyclonic Circulation in Arabian Sea Threatens Monsoon Progress

The arrival of the monsoon season in India is facing an additional hurdle this year, as a cyclonic circulation in the Arabian Sea adds uncertainty to its onset. Despite missing its scheduled arrival date over Kerala, the monsoon's progress along India's coast remains uncertain due to the cyclonic system.

According to a statement from the India Meteorological Department (IMD), cyclonic circulation is present over the southeast Arabian Sea, which is likely to result in the formation of a low-pressure area within the next 24 hours. This low-pressure system is expected to move northwards and potentially intensify into a depression in the southeast and adjoining east-central Arabian Sea within the subsequent 48 hours.

The terms "low-pressure area" and "depression" represent increasing levels of wind strength, with a cyclone being a stronger form of depression resulting from warm ocean surface temperatures and gusts of wind. The IMD's current weather models are divided on whether this cyclonic circulation will strengthen and move along the western coast or turn westwards towards Yemen and Oman.

D. Sivananda Pai, a meteorologist closely involved with monsoon forecasts at the IMD, stated that if it moved along the western coast, it would push the monsoon system upwards, but if it turned, then it would further take away moisture and stall the monsoon. He emphasized the need to wait and watch to see what has happened.

The IMD had previously predicted a monsoon onset date of June 4 over Kerala. This date, determined using a customized weather model, allows for a four-day margin of error. While favorable clouds and rain were observed in Kerala on June 4, the conditions have since weakened. Pai emphasized that the formation of such systems around this time is not unusual, but the monsoon system requires a slight push to progress further.

Rainfall alone does not determine the IMD's declaration of the monsoon's arrival. The agency considers factors such as minimum windspeed and depth in the atmosphere, Outgoing Longwave Radiation (a measure of cloudiness), and consistent rainfall over two days in Kerala when determining the monsoon's onset.

Roxy Mathew Koll, a scientist at the Indian Institute of Tropical Meteorology, explained that in El Nino years, a weak and delayed onset of the monsoon is often observed, along with an early withdrawal. He further mentioned that this year, they are observing a weak onset, and the formation of a cyclone, if it were to occur, would further stall the monsoon.

The IMD has predicted that monsoon rains from June to September are likely to be around 96% of the Long Period Average, which is a 50-year mean of 87 cm. This forecast places the rainfall at the lower end of what is considered "normal."