La Niña to return in September, may continue till winter
La Niña conditions associated with cooling of Pacific waters is likely to return in September, according to India Meteorological Department (IMD). Global meteorological phenomenon of La Niña is linked to very cold and harsh winters in India and above normal monsoon rains.
While above average rains are likely in August and September when La Niña conditions set in once again, IMD scientists said it was too early to give specific forecasts. La Niña conditions prevailed from August-September 2020 to April 2021. In India, La Niña was associated with an above normal monsoon last year, early winter onset as well as a harsh winter.
According to IMD Pune’s El Niño Southern Oscillation (ENSO) bulletin for July, currently, neutral ENSO conditions are prevailing over equatorial Pacific region. The latest Monsoon Mission Coupled Forecasting System (MMCFS) forecast indicates neutral ENSO conditions likely to continue up to July-September season, and August-October onwards cooling of temperatures over equatorial Pacific is likely to enhance and to reach to the La Niña threshold.
National Oceanic and Atmospheric Administration’s Climate Prediction Centre said on July 8 that La Niña is likely to emerge during the September-November season and last through the 2021-22 winter (66% chance during November-January).
“Our MMCFS model shows a high probability of La Niña developing from September. It is associated with good rains during the southwest monsoon season and because of clouding associated with rains, below normal temperatures are also expected. But we can’t tell yet what its impact will be on monsoon in August and September. IMD will soon issue a forecast for monsoon in August. La Niña has a negative impact on the northeast monsoon over peninsular India. That also needs to be monitored,” said O P Sreejith, head, climate monitoring and prediction group, IMD.
DS Pai, who heads IMD’s climate research and services, said La Niña conditions will develop at the end of monsoon so there are less chances of any adverse impacts like flooding etc. “We normally see cooler temperatures during La Niña years mainly due to cloud cover,” he added.
La Niña conditions developing in September will coincide with the post monsoon cyclone season. “While there is no direct correlation, a lot of studies have indicated that La Niña affects the track of cyclones developing over Bay of Bengal, they are more likely to move west wards,” said Sunitha Devi, in charge of cyclones at IMD.
Due to La Niña, the atmospheric circulation patterns change. The frequency of cyclone formation increases but slightly to the north from its normal position. So, you may see more cyclones forming near Odisha, West Bengal, Bangladesh and they have a higher chance of recurving as opposed to cyclones forming near Tamil Nadu or south Andhra Pradesh coasts during non-La Nina years, Pai had said last year.
A paper published in International Journal of Meteorology in 2019 on impact of ENSO on the Bay of Bengal tropical cyclone (TC) activity during post-monsoon (October–December) season for a period of 44 years (1972–2015) found that La Niña years are characterised by more frequent and intense cyclonic events compared with El Niño years.
There is 1% deficiency in monsoon rain since June 1 with 26% excess rain over Peninsular India; 3% excess over Central India; 17% deficiency over east and northeast India and 11% deficiency over northwest India.
IMD warned of an intense wet spell over northwest India from July 26 to July 30. The western end of the monsoon trough at mean sea level is running along its normal position while its eastern end runs close to the normal position. The western end is likely to shift northward during next 24 hours bringing widespread rains to the western Himalayas.
A cyclonic circulation is lying over North Bay of Bengal and neighbourhood at mid and upper tropospheric level. Under its influence, a low-pressure area is likely to form over North Bay of Bengal and neighbourhood around July 28.
Widespread rainfall activity with isolated heavy to very heavy rain is likely over Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Punjab, Haryana, Chandigarh and Uttar Pradesh till July 29 and reduction thereafter. Isolated extremely heavy rain (over 20cm) is also likely over Himachal Pradesh and Uttarakhand on July 27 and 28 and over northwest Uttar Pradesh on July 27.
Widespread rain with isolated heavy falls very likely over Konkan, Goa, ghat areas of Madhya Maharashtra during the next three days and increase to isolated heavy to very heavy rai over the region from July 29. Enhanced rainfall activity with heavy to very heavy rain is also likely over east and adjoining Central India (Odisha, Gangetic West Bengal, Jharkhand and Bihar) from July 27 onwards.