The Telegraph
Saturday , May 3 , 2014
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Rain for some, forecast for rest

- Storm strikes city but relief skewed

Rain played favourites on Friday evening but the forecast promises to be the leveller.

As parts of Calcutta soaked in the relief of a short but smart shower after a marathon dry spell, the rest of the city could do little but bemoan being on the wrong side of the rain divide.

The 38-day (54,965 minutes) wait for rain came to an end at 8.05pm in the form of a thunderstorm that lasted around 17 minutes in central Calcutta. Stronger spells of rain and thundershowers are forecast in the next few days, holding out hope for those who missed out on Friday.

The thundercloud that did the star turn on Friday originated in Jharkhand but weakened by the time it reached Calcutta, which is why the distribution of rainfall was skewed. Ultadanga and Palmer Bazar got 10mm and 6mm of rain respectively, while neighbourhoods in the south such as Ballygunge received only 3mm. Behala didn’t get any rain.

The places deprived of rain included Alipore, where the Regional Meteorological Centre is located. So when you look at Friday’s weather readings, don’t be surprised that officially Calcutta’s rainfall count is still 0mm.

The last time the weather office’s rain gauge came into play was on March 25, after which the city has been subjected to two spells of heatwave sandwiched between the usual sultry days that make up summer.

If the prayers of parched Calcuttans were partially answered on Friday, the real reward for surviving the hottest April in a decade is apparently yet to come. Weather scientists predicted that thunderclouds would develop regularly over the next three to four days.

According to the forecast, conditions look good for Calcutta to get a light spell of rain on Saturday. Between Sunday and Tuesday, the city is expected to get more intense squalls and rainfall.

“A cyclonic circulation over Bangladesh and a high-pressure belt over the Bay of Bengal are causing inflow of moisture into the air across the state. These systems are getting stronger, so thunderstorms are expected every day over the next few days,” said G.C. Debnath, director of the India Meteorological Department, Calcutta.

Rainfall would increase in quantity and be more widespread from Sunday, he added.

Friday’s storm, which was generated near Ranchi on the Chhotanagpur Plateau, delayed the first game of the India leg of IPL 7 in the Jharkhand capital and generated wind speeds between 35 and 45kmph in Jamshedpur.

By the time the storm hit town, the wind speed had fallen to 22kmph, less than half of the 45kmph required for it to meteorologically qualify as a squall.

“When a squall with a wind speed of at least 45kmph heads to the city from the Chhotanagpur Plateau, which is to the northwest of Calcutta, it is called a Nor’wester,” a weather scientist said.

Calcutta usually receives around five storms in April, most of them from that region. This year, there has been only one such storm, on March 25, with a rain count of 14.4mm.

Between then and Friday, the weather office had forecast rain or thundershowers at least on nine occasions. The last time the weather office had said that “thunderclouds would develop towards afternoon or evening” was on April 25, in the middle of a heatwave in the city.

The next day, the temperature did drop a little but there was not a hint of thundercloud over the city. This time, the weather office is convinced that the conditions are ripe for rain.

“We look for synchronisation of many factors for thunderstorms, which is why they are difficult to predict. The general perception is that heat and moisture are enough for Nor’westers to form, but wind also plays an important role. All these factors have come together now,” Debnath said.

Rain had been forecast earlier in the week but wind in the upper atmosphere blew the moisture north, triggering showers in north Bengal. The southern parts remained dry.

From Sunday onwards, the IMD expects favourable wind conditions and an abundance of moisture in the air across the state. Squalls are likely to be generated in the western districts of Bengal.

Rain is also expected to pull the temperature below normal. “We expect the maximum temperature to be around 34 degrees Celsius on Monday and Tuesday, which is why it is not going to be very uncomfortable despite high relative humidity because of moisture in the air,” a Met official said.

On Friday, the maximum temperature had dropped to 36.1 degrees Celsius, still a notch above normal, because of the partially cloudy sky. It was the coolest the city had been in 19 days.