Junior section students of Mahadevi Birla World Academy walk single file to their school bus after a short shower on Friday afternoon. Picture by Bishwarup Dutta
July had switched on the showers consistently for two days at the start to retain the “wettest month” crown but August has found firepower from the Bay to challenge the title.
The forecast on Friday says the first weekend of this month is set to be wet because of a cyclonic circulation brewing over the sea.
“A circulation has formed near the Odisha coast. It is likely to move towards Calcutta and bring steady rain from Saturday, for at least the next three days,” said Gokul Chandra Debnath, the director of the India Meteorological Department in Calcutta.
Met records say the city recorded an aggregate rainfall of 376mm in July, a tad above the normal range of 361mm based on figures between 1950 and 2000. “The figures suggest we got four per cent excess rainfall. Nineteen per cent rainfall on either side of the standard range is said to be normal in meteorological parlance,” a weather expert said.
The figures masked the truth that the rain distribution in the city was “heavily skewed” since as much as 190.4mm of rain was recorded in the first two days of July.
“Rain started on June 30 and continued till July 1. The figures for July 1 and July 2 are high because rainfall of the past 24 hours till 8.30am on a particular day is considered the total count for that day in meteorology the world over,” Debnath said.
July 1 got 91.8mm of rain, a tad below the 98.6mm of July 2.
The first half of August might turn out to be just as wet, riding the cyclonic circulation currently drawing moisture from the sea and expanding in mass.
The rainy start to July proved deceptive, though. The city received only 186mm of rain in the remaining 29 days of the month, which is a deficit of 44 per cent. The highest rainfall in 24 hours during the period was 42mm on July 3, followed by 18.6mm on July 15.
“The reason behind the scanty rainfall in the city throughout the month was the absence any depression over the Bay of Bengal. Although many relatively smaller formations such as cyclonic circulations and low-pressure areas did form, none went on to become a depression,” Debnath said.
“The Bay normally produces at least two depressions in July and these lead to widespread and uniform rainfall in the city. This July was relatively quiet and unproductive… no system had the strength to turn into a depression. Most of the circulations promised to deceive after landfall.”
A low-pressure area has atmospheric pressure lesser than its surroundings and draws air towards it. The stronger the system, the more air it attracts. On the seashore, it draws moisture-laden air and brings clouds and rain.
Like this year’s monsoon, the systems developing over the Bay had been weak thus far. “Hence, the spells of rain were short and rainfall was skewed,” a weather scientist said.
The weekly monsoon report released by the Alipore Met office said the city has been receiving deficient rainfall over the past few weeks. “Calcutta was recording excess seasonal rainfall of 13 per cent till July 16 but that turned into a 7 per cent deficit by the end of July,” the scientist added.
L.S. Rathore, the director general of IMD, Delhi, said the country has recorded a rain deficiency of 22 per cent till July-end. “We predict rain in most parts of the country in the next fortnight.”