Calcutta is caught between the demon and the deep sea days before Durga Puja — an active monsoon trough that is up to mischief and a make-or-break low-pressure area near the Andamans that promises to weaken it but could itself become a threat.
The city received a dunking on Monday afternoon, the trigger for the thunderstorm being an intense monsoon trough over central Bengal that has been drawing moisture from the Bay to land.
Several parts of north and central Calcutta were waterlogged, traffic went haywire and a city looking forward to festivity was left wondering whether this Puja would be remembered more for rain than revelry.
The only relief in sight is the low-pressure area about 1,000km from Calcutta, which has started a slow journey north. Weather scientists said the formation might suck in the strong monsoon trough, marking the end of the current spell of rain.
That is the good part. The not-so-good prospect is of the low-pressure area intensifying and coming very close to the Bengal coast, in which case Calcutta could be lashed by another spell of heavy rain right in the middle of Puja.
The only way the city can stave off this threat is pray that the low-pressure area veers towards the Andhra coast, as Mamata Banerjee suggested on Monday.
“Ma, anek brishti holo, aar na (Ma, there has been enough rain, please let there be no more),” the chief minister said while inaugurating minister Aroop Biswas’s Suruchi Sangha puja under an overcast sky.
Parts of north Calcutta had already gone under water by then.
“You can’t go pandal-hopping holding an umbrella over your head,” Mamata said.
Before leaving for the puja venue, she had called up the weather office to enquire about what’s in store. “They said there would be isolated rain, which means if it rains in Tollygunge, it might not rain in Jadavpur. Today, rain has flooded north Calcutta and it is still drizzling in the south,” the chief minister said.
Met officials said sporadic rain could continue for the next two days but there was little chance of daylong rainfall.
Sashthi on Thursday is likely to be dry but what happens after that depends on how atmospheric conditions influence the low-pressure area.
“The low-pressure area is more than 1,000km away from the Bengal coast at the moment and should reach the northern part of the Bay within three days if it travels at normal speed. By Sashthi, it should be able to pull the trough away,” said a senior official of the India Meteorological Department, Calcutta.
Till Monday evening, the northward movement of the low-pressure area looked more or less certain. It’s the behaviour of the system after this that would decide whether it rains in Calcutta or not.
“The low-pressure area would be very powerful by then. It could at this juncture travel to the Andhra coast or come towards the Bengal-Odisha coast. If it does come this way, the last phase of Puja, Navami and Dashami, could be very wet in Calcutta,” the official cautioned.
One of the characteristics of any low-pressure zone is to pull matter towards itself because the atmospheric pressure within the system is lesser than that of the surroundings.
“Such systems draw moisture from water bodies to cause rainfall or cold winds to bring chill, as the case might be. By the same principle, a larger, more powerful zone can pull a smaller zone towards itself,” the weather scientist said.