Kolkata: Rain relief on radar after driest July spell in 10 years

KOLKATA: The city’s driest July so far in a decade is set to end with a wet spell as a low pressure — set to form over Bay of Bengal close to the Bengal coast — is likely to trigger rain across south Bengal on Friday and Saturday. It could be preceded by thunderstorms on Wednesday and Thursday, which is expected to bring the mercury down. The seasonal rain deficit in Kolkata touched 66% till Tuesday, the highest since at least 2010. Kolkata recorded a maximum temperature of 35.2°C on Tuesday.
Following a 69% rain deficit in June, Kolkata has remained dry this month as well. With no rain-triggering systems forming, day temperature has been unusually high. But the intense heat and the sliding down of the monsoon trough from north Bengal have combined to turn the conditions favourable for thunderstorms this week. “The sky could remain cloudy and the city could be lashed by thunderstorms on Wednesday and Thursday. On Friday, a low pressure is set to form over Bay of Bengal close to the Bengal coast. It could have a significant impact on Kolkata and the whole of south Bengal. We expect moderate, if not heavy rain, to lash the region,” said Regional Meteorological Centre (RMC) director GK Das.
He added that this is set to be the first major rain-triggering system to form after the onset of monsoon that was delayed by around 10 days. While north Bengal has been soaked by heavy rain since June, south Bengal has remained exceptionally dry. “Unless we have frequent low pressures, rainfall will be scanty. This is what has happened this monsoon so far. But the trend may change,” said Das.
While July rain count in Kolkata has frequently been lower than normal over the last 10 years, this year’s deficiency has been the highest. Between 2010 and 2018, Kolkata had a July rain deficit six times. Last year, the deficit was 51%. This time, the seasonal stood at 66% till Tuesday while the city deficit, too, was more than 60%. Gangetic Bengal has a seasonal deficit of 55%. “This week’s rain will lower the deficit. But it is unlikely to wipe it out completely. In fact, the deficit could remain quite high despite the low pressure-triggered rain that is expected this week. We need at least a couple of more such systems to narrow the gap,” said a weather scientist.
Unless we have heavier showers more regularly, the mercury will remain high, said Das. “Monsoon rain is driven by low-pressure systems. The more they form, the more rain we will receive. They have been rare in the region so far. And the mercury has been climbing quickly in the absence of the dust-particle shield,” added Das.
“Even though the deficiency is very high so far this month, there is still enough time to make it up. August is also the peak monsoon period and it often rains heavily in September. So, the final count will depend on the number of systems that we have in the region in the coming weeks,” said Das.