The forecast, issued after a meeting of experts from different disciplines at the met office, said the monsoon would move out of Bangladesh by the second week.
Rains are likely to be normal during October, the forecast said, adding that the rainfall was 16 per cent less than normal last month despite formation of a deep depression and a couple of low pressures in the Bay of Bengal, which moved away towards India.
The cyclone season in the Bay begins in October and runs until April. But cyclones in December are rare. The last cyclone in December was on December 15, 1965.
The most devastating cyclones took place on November 12, 1970, April 30, 1991 and latest on November 15, 2007, killing thousands, whipping up sea surges and high winds.