India has so far witnessed four deep depressions—or cyclones—against the usual one or two in the ongoing monsoon season due to an increase in sea surface temperatures. La Nina, a phenomenon that leads to more monsoon showers in India and causes floods which is expected to emerge by the end of September or October is also contributing to it, according to meteorologists.
A deep depression can cause torrential rains and flooding. The frequency and intensity of low-pressure areas turning into depressions have increased over the past five-six years and meteorologists attribute it to climate change.
“The frequency and intensity of low-pressure areas and depression has increased over north Bay of Bengal due to warm up of SST (sea surface temperature). This is not a usual phenomenon. There’s typically a gap of a fortnight or 20 days between the formation of two depressions, but now we are noticing one after another low-pressure areas intensifying into depressions quickly,” said Mahesh Palawat, Vice president meteorology and climate change at Skymet, a private weather forecasting agency.
He attributed warming SST to climate change.
“Climate change is one of the factors because air temperature is rising and the capacity of air to hold moisture is also increasing. So, whenever such a weather system develops, it intensifies rapidly. This was not the case until the last decade. Since the past 5-6 years we have been noticing there is an increase in frequency and intensity of these weather systems,” Palawat informed.
“The deep depression over Gangetic West Bengal and adjoining areas is the fourth and probably the last one in this monsoon season. Usually, one or two depressions form during July and August, the rainiest months,” he added.
Notably, in the 2024 monsoon season (June-September) Cyclone Asna, an unusual event given its timing and location, was the first cyclone to form in August in the North Indian Ocean region since 1981 and the first in the Arabian Sea since 1976.
It originated from a deep depression over Gujarat, which intensified over the Arabian Sea. This rare occurrence is attributed to an unusual monsoon wind system, characterised by strong easterly winds and a significant monsoonal event known as the Boreal Summer Intra-Seasonal Oscillation.
Cyclone Yagi, the most powerful to hit southeast Asia this year, caused severe floods in Myanmar, resulting in at least 230 deaths and causing heavy showers in Delhi, Uttar Pradesh and Uttarakhand, carried by westerly winds.
The latest depression has formed over northeast Bay of Bengal and adjoining southeast Bangladesh coast. Due to this, eastern India has been receiving incessant rain since Friday.
West Bengal, Jharkhand and Bihar have recorded 658%, 449% and 114% surplus rain in the 24 hours ended 8 am Sunday. The country has recorded 857.5 mm or 8% above normal rain since the beginning of the Southwest monsoon.
The low-pressure area will likely retravel towards in a westerly direction across north Odisha, Jharkhand and north Chhattisgarh and turn into a depression.
There may be marginal weakening of the system as it travels to land area because moisture will be depleted. It is expected to maintain its intensity as a depression to north-east Madhya Pradesh and thereafter get regenerated into a well-marked low-pressure by Wednesday or Thursday and bring heavy to extremely heavy precipitation.
“Moreover, we are entering La Nina phase. When El Nino is there, monsoon rain in southeast Asia is less than normal, which we had seen last year. Now, we have already entered neutral phase, and La Nina is expected to emerge by October or November,” Skymet’s Palawat said.
In its monthly weather forecast, the India Meteorological Department said rain in September in the country is most likely to be above normal (>109 % of the Long Period Average, or LPA) and warned of flash floods, landslides, mudslides, and landslips in some regions.
