India Meteorological Department (IMD) declared the onset of the monsoon over Kerala on Thursday but rain watchers eagerly waiting for typically rainy days on ground are a disappointed lot. The cold and wind-swept conditions which help them take a call by themselves are missing, too.

It was brightly sunny through the day in Thiruvananthapuram, the State capital, under clear blue skies. Sparse cloud formations made a fleeting presence at times, but their footprints didn’t grow to a size as to offer some offer shade anywhere in the city. The conditions reminded one of the much hotter mid-May.

Monsoon loses the plot

And there hangs a tale. Building onset conditions seemed to have lost the plot during the pre-monsoon season (March-May) when the state received the highest seasonal rainfall in the last 50 years, and the fourth highest in a century with cyclones “Tauktae” and more recently “Yaas” nearly flooding it as they sped away upcountry.

Roxy Koll, climate scientist at the Indian Institute of Tropical Meteorology, says that the western tropical Indian Ocean has warmed for more than a century at a rate faster than any other region in the tropics and is the largest contributor to the overall trend in the global mean sea surface temperature (SST).

Tropical cyclone heat potential (THCP) is a measure of heat in the upper ocean that is available as an energy source for cyclones. The warm Arabian Sea waters can support cyclogenesis, Koll added.

‘Yaas’ delivers damage

Sushant Puranik, Faculty for Weather Research and Forecasting, Department of Atmospheric and Space Science, and ISRO-Junior Research Fellow at the University of Pune says: “Yaas intensified rapidly due to conducive atmospheric conditions and drained out the moisture and energy (of the monsoon system).”

Winds too had converged over the system. As a result, the eastern arm of the monsoon over the Bay of Bengal became more powerful at the expense of the western arm that moves through the Arabian Sea.

This led to the delay in the arrival of the monsoon, he pointed out. Formation of ‘Yaas’ impacted the required wind speed levels over Arabian Sea, while the value of OLR has also not been achieved.

Hide and seek by clouds

OLR refers to Outgoing Long-wave Radiation and is a proxy to the build-up of rain-bearing clouds over a prescribed area over the South-East Arabian Sea off Kerala. The lower the OLR value, higher the cloud cover. The OLR did not hit the required number even on Wednesday (June 2), as per available data.

GP Sharma, President, Meteorology and Climate Change, Skymet Weather, said Kerala had been witnessing widespread heavy pre-monsoon rain in May, signaling a great start for the monsoon. But the twin cyclones blew away chances of an orderly onset and onward progress of the seasonal rain system.

Twin cyclones blow it away

Sharma quoted INSAT 3D OLR and NOAA data analysis to state that the OLR was lowest on May 22, 25 and 26 when Kerala received heavy to very heavy rainfall. But the value has crossed the minimum threshold and has been rising ever since, indicating lesser cloud cover in the region. Weathermen now count on formation of likely cyclonic circulations on either side of the peninsula later during the first week of June to strengthen the monsoon current. A trough is already seen running off the West Coast, but Sharma said it is not well-evolved to trigger an explosive start to the proceedings just yet.

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