Monsoon extends with more rainfall, cyclone likely in October

• 33% above normal rainfall in September
• 1-3 low pressures may develop in Bay of Bengal in October
• 1 low pressure may develop into a cyclone this month
• Till 12 October, there will be rain in Sylhet, Rajshahi, Mymensingh and Rangpur divisions
• Heavy rain likely in Chattogram, Barishal and Sylhet divisions till 4 October
• Landslide risk warning issued in Chattogram division

Bangladesh typically experiences its monsoon season from June to mid-October, during which the majority of rainfall occurs. Traditionally, July sees the highest rainfall, followed by a gradual decrease. 

However, this year's monsoon extends with unprecedented rainfall in August and September. Bangladesh faced 46% more rainfall than usual in August, and a further 33% above normal in September. 

According to the Bangladesh Meteorological Department (BMD), the monsoon may last longer than usual. In October, the country's East-southern part may face flooding again and also one Cyclone may occur. 

Meteorologist Mostofa Kamal Palash, a PhD researcher in meteorology and climate at the University of Saskatchewan, Canada, told TBS that Bangladesh has seen record rainfall at the tail end of the season due to an active monsoon. 

"The axis of monsoon troughs now runs through Uttar Pradesh, Bihar, West Bengal to Assam, crossing central Bangladesh. As a result, the rainfall may persist longer," he said.

BMD today issued a local warning signal no 3 for all seaports, including Chattogram, Cox's Bazar, Mongla, and Payra due to the continued formation of deep convective clouds over the North Bay of Bengal and coastal areas.

The forecast urged fishing boats and trawlers operating in the North Bay to proceed cautiously and stay close to the coast until further notice.

BMD also issued a warning of heavy to very heavy rainfall in three divisions- Chattogram, Barishal, and Sylhet in the next 48 hours from 6am Wednesday. The circular also warned about the landslide risk in the Chattogram division.

The Met Office reported that six low-pressure systems formed in the Bay of Bengal over the past two months, with four developing into depressions.

Meteorologist Muhammad Abul Kalam Mallik highlighted that a low-pressure area is expected to form over the North Bay on 4 October. He noted that compared to previous years, this year's monsoon is expected to last longer, with repeated low-pressure systems and more rainfall. 

"Climate change and shifting monsoon patterns are contributing factors to the excessive rainfall," Mallik added.

In its long-term weather forecast, Bangladesh met office says 1-3 low pressures may develop in Bay of Bengal in October and one low pressure may develop into a cyclone this month. 

Meteorologist Abul Kalam Mallik, analysing 133 years of October data, said since 1891, 51 cyclones have occurred in the Bay of Bengal, 43 of which were categorized as very strong. Of these, 11 severe cyclones crossed the Bangladesh coast, making October a historically active month for cyclones in the region. 

One of the deadliest was the cyclone of 31 October 1960, which killed over 500,000 people. The tidal surge reached 6.1 metres, with a flood height of 20 feet in Chattogram. More recently, on 25 October 2022, Cyclone Sitrang impacted Bangladesh, damaging 10,000 homes and affecting 6,000 hectares of crops.

While heavy rainfall is expected to cause short-term flooding in some northern, northeastern, and southeastern hilly areas, the Flood Forecasting and Warning Centre's Executive Engineer, Sarder Udoy Raihan, said the main rivers of Sylhet and Chattogram may rise over the next three days.

"Waterlogging in some areas, such as Cumilla, may worsen with continued rainfall, and parts of Chattogram could experience flooding if rains intensify," he added. 

However, the flood situation in the northern region has normalised, with no rivers currently above the danger level, he added. 

Meteorologist Mostofa Kamal Palash told TBS that heavy rains began in various parts of the country on Wednesday and are expected to continue until 6 October. Sylhet and Chattogram divisions are likely to experience flooding due to increasing rainfall, with landslide risks in Chattogram's hilly areas.