Why Bangladesh seeing so much rain in October?

Although October is typically a month of retreating monsoon with clearer skies, heavy rainfall has continued across Bangladesh throughout the month, raising questions about how normal such weather is.

Typically, rainfall decreases towards the end of the monsoon season, which usually ends by 15 October. However, in recent years, late-season rainfall has increased, a trend attributed to global climate change.

According to the Bangladesh Meteorological Department (BMD), Dhaka recorded 152 millimetres of rain in the first nine days of October, while the nationwide total reached 5,739 millimetres. Forecasts suggest rain may continue until mid‑October.

Meteorologists said the main cause of this month's rainfall was a deep depression that formed over the Bay of Bengal at the beginning of October. However, showers have persisted even after the system weakened.

Md Shahinul Islam, a meteorologist at the BMD, told The Business Standard that the analysis of the past five years shows October rainfall cannot be considered abnormal. "So far, this year's rainfall is within the usual range. In fact, some rain may also occur in November and December," he said.

Senior meteorologist Md Bazlur Rashid noted that rainfall in early or mid‑October is common, as the monsoon typically withdraws during this period. "We must remember that even in December 2023, there was significant rainfall," he said.

BMD records show that October rainfall has varied widely in recent years: Dhaka recorded 297mm in 2022, 326mm in 2023, and 258mm in 2024. Nationwide totals ranged from 8,642mm in 2021 to 19,011mm in 2024.

On 1 October this year, Dhaka also saw its highest 24‑hour rainfall of 2024, with 206mm recorded.

Rashid further said, "Rainfall patterns in Bangladesh have shifted over the past decade. A few years ago, June usually received normal or above‑normal rainfall after the monsoon began, and rain would decrease toward the end of the season.

"But over the past 8–10 years, more rain has been occurring at the end of the monsoon. This year, rainfall has been continuous throughout the season, higher than normal."

He added that while heavy downpours in short bursts have been rare this year, frequent intermittent rain has continued throughout the monsoon, putting early winter crops at risk of loss.

According to the BMD data, this monsoon had more rainy days than usual, damaging roads and crops. July and August saw above‑normal rainfall, with July recording nearly 24% more rain than average, while Dhaka experienced 45% above‑normal rainfall. September, however, was drier than usual.

Meteorologists expect rainfall to decrease over the next few days, though a new low‑pressure system may form over the Bay of Bengal later this month, potentially extending rains into November.