Why was Met forecast way off the mark?
The special bulletin that Bangladesh Met Office issued on Monday morning had warned that Cyclone Sitrang would make landfall anytime between Monday midnight and Tuesday morning.
Based on the prediction that remained almost unchanged till Monday afternoon, the state minister for disaster even came up with a specific time of the cyclone hitting the coast -- 6:00am.
However, it started moving over land around 9:00pm on Monday, much ahead of the weather office's predicted time.
By the time the Met office issued its updated bulletin at 9:00pm announcing the cyclone's landfall, Sitrang had already started sweeping the country.
The incorrect predictions sparked uproar on the social media, with netizens questioning the country's weather prediction mechanisms.
Some even pointed out that such misinformation may cause further disasters during a cyclone.
But why were the predictions inaccurate?
Experts say it was because the Met office lacks sufficient equipment to measure the meteorological variables.
Speaking to The Daily Star, Mohan Kumar Das, executive director of the National Oceanographic and Maritime Institute, said, "Bangladesh does not have sufficient buoy or ship observation data to measure the meteorological variables in the north Bay of Bengal."
He added that the tropical Cyclone Sitrang travelled through the north Bay and it was found there was almost six to seven hours of time gap in the forecast given by the BMD and various numerical models in their 48-hour forecast.
A similar error was also found in the 48-hour forecast by the Regional Specialized Meteorological Centre, he said.
He further said almost all the radar systems of Bangladesh are non-functional.
"Coastal radar and radar data utilisation are very essential for the accurate forecast of tropical cyclones with sufficient lead time."
Das, also joint secretary of South Asian Meteorological Association, said time and location-specific cyclone predictions require a continuous synoptic time scale (every three hours); ocean observation (buoy, ship) monitoring system; a modern functional radar system; qualified and capable scientists; and Ocean Forecasting Research initiatives.
He said forecasting tropical cyclones is a complex procedure.
"Regional cooperation, and sophisticated Ocean Forecasting research initiative is necessary."
BMD officials, however, said they predicted the cyclone almost accurately although there were some time gaps in the landfall prediction, which occurred due to the cyclone's unpredictability.
Md Bazlur Rashid, meteorologist of BMD, said, "This cyclone was exceptional as it continuously changed its directions from the beginning. As it was a nominal [small] cyclone, its volatility was high and so was the uncertainty [in its behaviour]. That's why there was some time gap [in the predictions]."
Asked whether they analysed the open-source data and other available models, he said they considered all the information, but it took some time for them to make a concrete decision.
He, however, said they had made the correct prediction as it was said the wind speed could be 62-88kmph and the BMD recorded the highest to be 75kmph.
"So, our prediction was right."
Asked about buoy observations in the ocean, meteorologist Abdul Mannan said, "Yes, we don't have any instrument in the ocean. If we did, we could have observed the situation more intensely and accurately."
SITRANG'S UNIQUE FEATURES
Met officials said Sitrang's distinct feature was its wide area coverage of heavy rainfall and fast movement.
"In our recent history with cyclones, we did not earlier find any that covered such a wide area with heavy rainfall. In many places the average rainfall was more than 200 millimeters," Mannan said.
According to the BMD, Barishal division witnessed the highest rainfall -- 324 millimeters, while Dhaka recorded 255 millimeters.
He added that the cyclone was so fast that it took only nine hours to cross the Bangladesh border from south to north.
"Usually, the lifespan of a cyclone is around five to seven days," he said, adding that Sitrang's was only three.