The rainfall is hard to forecast and varies considerably but scientists say climate change is making the monsoon stronger and more erratic.
At least 55 people have been killed and more than a million affected by two weeks of torrential rains causing floods and landslides in southeast Bangladesh, officials said Sunday, reports The Hindu.
Administrators of four of the worst-hit districts said floods and landslides since August 1 killed 21 people in Cox's Bazar, 19 in Chittagong, 10 in Bandarban and five in Rangamati.
"These are some of the heaviest rains in recent years," Bangladesh Meteorological Department chief Azizur Rahman told AFP.
He said 312 millimetres (12 inches) of rainfall was recorded on August 7 alone.
Officials said heavy rains lashed the region until August 11, triggering flash floods that caused rivers to burst their banks and inundate hundreds of villages.
It was only possible to confirm how many were killed after the floodwaters began to recede.
The summer monsoon brings South Asia around 80% of its annual rainfall, as well as death and destruction due to flooding and landslides.
The rainfall is hard to forecast and varies considerably but scientists say climate change is making the monsoon stronger and more erratic, while deforestation and building on hillsides has made flash floods worse.
"In Cox's Bazar some 600,000 people were affected by the floods," district administrator Shaheen Ibrahim told AFP.
Bangladesh is home to one million Rohingyas who fled a military crackdown in Myanmar and now live in some three dozen camps built on cleared forest and hill slopes in Cox's Bazar.
"At least 21 people were killed", Ibrahim said.
Refugee commissioner Mizanur Rahman said four Rohingyas were killed, including a child and her mother who were buried under a landslide.
"We have relocated around 2,000 people to safe places who are at risk of landslides in the camps," he told AFP.
Hundreds of villages were swamped in Chittagong, Bangladesh's second-largest city and home to its biggest port, in what residents said was some of the heaviest flooding in decades.
"The flood damaged at least 5,000 thatched houses," district administrator Abul Bashar Mohammed Fakhruzzaman told AFP.
"At least 19 people have died from the floods. We recovered some bodies from the Sangu river after floodwater receded in the past few days. Some 450,000 people were affected by the floods."
Transport between Chittagong and Cox's Bazar was cut for a few days and newly laid railway tracks were damaged, he said.
The rains also triggered a major flash flood in the hill district of Bandarban, where administrator Shah Mujahid Uddin said at least 10 people were killed.
Five people were killed in the Rangamati hill district, where heavy rains cut off some 23,000 people, administrator Mosharraf Hossain said.
Bangladeshi authorities have sent food and relief to the worst-affected region, said Shahina Sultana, a senior government official in Chattogram region, the new name for Chittagong.
Five people were still missing, she said.
"The government is doing everything in its power to support people," she said.