Cyclone Biprajoy in Arabian Sea puts cloud over monsoon progress
In a statement, IMD admitted that the system is “likely to influence the monsoon progress” , although it stated that an update would follow on Wednesday.
Its name may have “joy” in it, but it actually means calamity in Bengali, which is apt because Cyclone Biprajoy, which developed in the Arabian Sea, may adversely affect the monsoon, which is already delayed this year.
Read here: Cyclone Biparjoy: How did it get this name, where is it headed to? All details
“Biparjoy is not good for our monsoon because it is pulling all the moisture along with it away from the Indian coast. Its formation is not near the India coast and hence monsoon’s progress will remain very poor until around June 12. It may strengthen the cross-equatorial flow after the cyclone dissipates, but that’s a long way away. We are closely monitoring onset conditions over Kerala but cloud cover has reduced owing to the rapidly intensifying deep depression over Arabian Sea. Its intensity will most definitely reach very severe cyclone phase. We are still hoping onset happens soon,” said a senior IMD official who did not wish to be named.
In a statement, IMD admitted that the system is “likely to influence the monsoon progress” , although it stated that an update would follow on Wednesday.
To be sure, the date of the monsoon’s onset is not correlated with its performance, although the emergence of an El Nino phenomenon (warm currents in the equatorial Pacific Ocean which is correlated with poor monsoons) is a matter of concern. IMD has predicted a normal monsoon with rainfall that is 96% of the long period average. This is at the lower end of the normal category. According to India’s agriculture ministry, almost half of India’s farmed area, accounting for around 40% of production, is rain-fed, making the monsoon critical. With 47% of the country’s population dependent on agriculture for their livelihood (according to this year’s Economic Survey), a bountiful monsoon has a direct correlation with a healthy rural economy.
On May 16, IMD predicted that the monsoon was likely to make onset over Kerala on June 4 with a model error of +/-4 days. The monsoon normally sets in over Kerala around June 1. IMD has three criteria for declaring the monsoon after May 10: 60% of the 13 stations in Kerala, situated in Minicoy, Amini, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kudulu and Mangalore in Karnataka report rainfall of 2.5mm or more for two consecutive days; a certain depth of westerlies; and low satellite derived Outgoing Longwave Radiation (OLR). OLR represents the total radiation going to space emitted by the atmosphere or extent of cloudiness. These three have not been met yet, and IMD has not stated when they are likely to be met.
Read here: Cyclone Biparjoy will have no impact over Maharashtra: IMD
To be sure, IMD broke with its own protocol and declared an early arrival of the monsoon last year when the first criterion was not met, drawing criticism from experts.
“IMD forecasts indicate a very severe cyclone in the Arabian Sea, driving the moisture away, instead of the expected monsoon onset. An exceptionally warm Arabian Sea, a weak monsoon onset, and favourable Madden Julien Oscillation conditions are favouring this cyclone,” tweeted Roxy Mathew Koll, climate scientist with Indian Institute of Tropical Meteorology. “Sea surface temperatures (SST) SSTs are 31-32°C, 2-4°C above climatological mean. This is clearly the climate change link, as Arabian Sea warming is favoring more intense cyclones… A strong monsoon means southwesterly winds in the lower atmosphere and northeasterly in the upper. This vertical wind shear is now weaker than usual in the Arabian Sea, which means a weak monsoon. This helps the cyclone to develop vertically,” Koll added in another tweet.
“The long-term Indian Ocean warming and the developing El Niño – both has the potential to weaken the monsoon. Are we having frequent delayed onsets? We don’t know yet,” he said in a third.
“If the cyclone heads towards Oman/Yemen as shown currently by global models, the monsoon progress may get hampered and monsoon will stall for few days. If it goes north initially, as currently shown by IMD and Joint Typhoon Warning Centre, then initially it will help monsoon onset. After that when it heads northwest (as shown by global models) then monsoon progress likely to be impacted,” explained Vineet Kumar Singh, researcher, Typhoon Research Center, Jeju National University, South Korea.
Apart from rainfall, another criterion for declaring the onset of the monsoon has also been hit.
“The problem is that the cloud cover over Kerala has reduced due to the development of this depression over Arabian Sea. It is one of the criteria that should be met. We are hoping that the onset criteria are met during the next two days. When the developing cyclone moves away from the Indian coast it can pull the monsoon current along with it leading to very weak progression of monsoon over the Indian mainland. That can impact sowing of crops. We are carefully watching the system now,” said Mahesh Palawat, vice president, climate and meteorology at Skymet Weather, a private weather forecaster.
Skymet has forecast “below normal” rainfall during the monsoon season between June and September, attributing the deficiency to a strengthening El Nino phenomenon.
Models are not providing consensus on the landfall location of Biparjoy, officials said. “This is an intense cyclone and the Arabian Sea is very warm. It will intensify over the ocean but we haven’t provided any landfall location because there is no consensus. Sometimes these cyclones also recurve,” added the IMD official cited in the first instance.
But there is also a minority expert view that the cyclone could help the monsoon. “Some monsoon vortices develop in to a cyclone. It’s rare but does happen. In 1979 there was a monsoon vortex that intensified into a cyclone and moved over Gujarat. So, it can happen. This cyclone also developed from a monsoon vortex, a kind of low-pressure system forming on the northern edge of the monsoon flow. Rarely they can intensify like in the case of this cyclone. My reading based on the models is the cyclone will help our monsoon during the onset phase bringing good rains to the west coast. What happens thereafter will have to be monitored depending on the track of the cyclone,” said M Rajeevan, former secretary, ministry of earth sciences. Onset vortices occur over the Arabian Sea where the sea surface temperature spikes just before the onset of monsoon.
Read here: Number theory: How have El Nino and delayed onset affected monsoon in the past
The deep depression over southeast and adjoining east-central Arabian Sea moved nearly northwards with a speed of 4 kmph during last six hours, intensified into a cyclonic storm Biparjoy on Tuesday evening over east-central and adjoining southeast Arabian Sea about 920km west-southwest of Goa, 1,050km southwest of Mumbai, 1,130km south-southwest of Porbandar and 1,430km south of Karachi.
It is likely to move nearly northwards and intensify gradually into a severe cyclonic storm over east-central Arabian Sea during next 24 hours.