BHUBANESWAR: Odisha has witnessed three cyclones in many years but it is Yaas that kept all guessing till the very end. It is perhaps the only summer cyclone in recent times that triggered floods in some rivers due to heavy rainfall in their catchment.
Although India Meteorological Department (IMD) claimed to have correctly predicted the landfall zone, its forecast on maximum sustained wind speed lacked precision.
The wind speed during landfall was less than the estimated 130 kmph to 140 kmph, which was corrected from 155-165 kmph gusting up to 185 kmph. The highest recorded wind speed was 45 knots (around 85 kmph) at about 8.30 am at Balasore.
Emeritus Professor at the School of Earth, Ocean and Climate Sciences of IIT-Bhubaneswar UC Mohanty said the strong vertical wind shear disturbed the system which lost strength due to a rise in central pressure resulting in less vaporization.
“It also came very close (around 40 km) to the coast unlike the last two cyclones and weakened before landfall leading to different predictions by different models. Like Aman, it brushed the Odisha coast before moving towards northwest thereby causing less devastation,” he observed.
Apart from the landfall zone, the wind speed was also less in Khurda and Cuttack. It was somewhere between 50 kmph to 65 kmph against the prediction of 80 km to 90 kmph gusting up to 100 kmph. There was neither any precipitation nor any gusty wind.
From the initial prediction of a large band of landfall area between Paradip and Sagar Islands, the IMD had narrowed it to the area between north of Dhamra and South of Balasore after making one more prediction of the storm hitting the coast around Balasore.
The cyclonic system behaved very peculiarly leaving everyone bewildered. Even after the landfall, it caused more damage in West Bengal than Odisha where it is said to have hit the coast and its impact lasted for nearly 12 hours. Interestingly, the image taken by Japanese satellite Himawari 8 indicated that the western edge of the system had already touched the land southwest of Dhamra by 5.30 am.
As the forecast continued to change, for some time, the government officials engaged in evacuation and contingency plans were confused too.
“Initially we were told to be prepared for Bhograi, but within 10 to 12 hours it was changed to Bahanaga. I have experienced at least four cyclones and closely monitored the systems for years but never had seen such suspense,” said a senior official.
When the cyclone was actually hitting the coast, the IMD bulletin issued at 8.30 am read: “The landfall process would commence during next couple of hours.” But the next bulletin after 45 minutes said the landfall process has commenced. Unlike the previous cyclones, the devastation was less in the landfall zone.
IMD Director General Mrutyunjay Mohapatra said, the national forecaster was spot on as far as the landfall of the system is concerned. “As predicted, the cyclone made landfall 20 km south of Balasore before moving northwestward. The devastation was less as the system had weakened and lacked intensity,” he said.
Wind speed, he said, is generally not equally distributed in all cyclones. It depends on the characteristics of the systems and topography. Since there was a fall in intensification, the estimated wind speed was around 130-140 kmph at the time of landfall, Mohapatra added.
The Joint Typhoon Warning Centre (JTWC) too changed the location of the landfall from Bhitarkanika to Budhabalanga estuary (Balaramgadi mouth), north of Chandipur. Its wind speed prediction (45 knots) after landfall was, however, almost accurate. The European model ECMWF had also projected a wide range of possible paths up to the Sagar Islands for the cyclone.
“Yaas was different from others. Its eye had not developed properly and the whole region was overcast. Its center was at one place and the clouds were at another place and it lost intensity after it interacted with the mangrove forest and the landmass,” pointed out Director of Centre for Environment and Climate (CEC) at SOA University, Sarat Chandra Sahu, who had predicted that the wind speed would be between 80 to 100 kmph while crossing the coast.
As per JTWC, the system charted a near-northerly course (355 degree and 350 degree) throughout Tuesday. This, in fact, resulted in the cyclone remaining in shallow water for longer periods thereby deriving less latent heat from vaporisation and condensation that provides the muscle to a cyclone.