Natural Disasters

‘Dynamic system’: Why Mocha is a storm with a difference

A careful analysis shows that the prediction of the storm’s wind speed has been modified several times in the past 3 days  

By Jayanta Basu
Published: Saturday 13 May 2023
Photo: @WMO / Twitter

Cyclone Mocha, which is all set to make landfall at noon on May 14, 2023, has always remained a step ahead of prediction.

A careful analysis of India Meteorological Department (IMD)’s bulletins in the past three days shows that the prediction of the storm’s wind speed has been modified several times. 

Initially, IMD had predicted the formation of a ‘very severe cyclonic storm’, which was later upgraded to ‘extremely severe cyclonic storm’ and now a super cyclone is on the cards.

In its Bulletin number 3 issued at 9.15 am on May 10, IMD only predicted a very severe cyclonic storm and predicted, for the first time, the landfall speed of a maximum 130 kilometres (km).

The maximum sustained speed was calculated to be in the range of 140-150 km per hour (kmph). Over the next three days, IMD continued to predict stronger cyclones and modified the maximum sustained speed six times and the speed at landfall by five times.

On May 13, 2023, at 10 pm, IMD predicted in its Bulletin 29 that the maximum sustained speed of Mocha can reach up to 210-220 kmph with gusting at 240 kmph. The landfall speed was pegged at 180-190 kmph, with gusting at 210 kmph.

At 4.45 pm, IMD had predicted in its Bulletin 27 that the maximum sustained speed of Mocha can reach up to 200-210 kmph with gusting at 230 kmph.

The landfall speed was pegged at 170-180 kmph, with gusting at 200 kmph. The bulletin immediately before predicted the same wind speed.

Barely four hours back before the Bulletin 27 was issued, at 12.30 pm, the Department predicted in Bulletin 25 that the maximum sustained speed of Mocha could reach up to 190-200 kmph, with gusting at 220 kmph. The landfall speed was pegged at 150-160 kmph, with gusting at 175 kmph.

Clearly, the intensification has occurred over the last three days far too rapidly compared to prediction.

The speed, both during the path and landfall, increased around 40 per cent, compared to initial prediction: 150 to 210 kmph in maximum gusting while on cyclone course and 130 to 200 kmph at landfall.

However, the predicted landfall point has remained constant over the predictions.

“It is a dynamic system and we keep on upgrading as it happens; you cannot be fully accurate in prediction; but we continue to upgrade the prediction early enough so that the damages can be minimised,” Mrutyunjay Mohapatra, director-general of IMD told this reporter on May 13 evening.     

‘Super Cyclone’

“It (Mocha) is very likely to move north-northeastwards and cross the southeast Bangladesh and north Myanmar coasts between Cox’s Bazar (Bangladesh) and Kyaukpyu (Myanmar), close to Sittwe (Myanmar) around noon of 14th May, 2023 as an Extremely Severe Cyclonic Storm with maximum sustained wind speed of 170-180 kmph gusting to 200 kmph,” Bulletin 27 read.

A senior IMD official pointed out that a system is called ‘super cyclone’ when the maximum sustained speed crosses 221 kmph; which is barely higher than the presently predicted speed.

“At this point we only say that am extremely severe cyclone will be formed with a wind speed as predicted but further intensification is possible by tonight,” Mohapatra said.

“One cannot rule out the possibility of a super cyclone; but whether it technically crosses the super cyclone threshold or not clearly the devastation will be significant … whether super cyclone or very severe cyclone; area of about 150 km from the landfall will receive significant damage,” said an IMD official.

Raghu Murtugudde, an earth scientist and weather expert attached to Indian Institute of Technology Mumbai and University of Maryland, pointed out that “further rapid intensification is possible as the Bay is warm and cyclone is moving slowly over the ocean and gaining lots of energy; and just before hitting the land it may reach super cyclone category”.

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