An India Meteorological Department (IMD) update on Thursday said that the rain-driving upper air cyclonic circulation over north Bihar and neighbourhood persisted from overnight.
A trough from this system ran down to south Bay of Bengal, the IMD added.
According to the National Centre for Medium Range weather Forecasting (NCMMRWF), the system is expected to move towards sub-Himalayan West Bengal during next 24 hours before moving further east to over Assam.
An NCMRWF outlook cited model predictions suggesting the formation of a cyclonic circulation over east-central Bay of Bengal and adjoining area around October 10. The system is likely to intensify, the forecast added.
The IMD has forecast fairly widespread rainfall with isolated heavy to very heavy falls over sub-Himalayan West Bengal and Sikkim during the next 24 hours and over the north-eastern States during the next two days.
Weather is likely to remain mainly dry over west and central India and plains of north-west India.
Satellite images on Thursday showed convective clouds over parts of south-east Bay of Bengal, south Andaman Sea, sub-Himalayan West Bengal, Sikkim and the north-eastern States.
A warning valid for the next two days said that heavy to very heavy rainfall is likely at a few places over the north-eastern States.
Isolated heavy to very heavy rainfall has been forecast over sub-Himalayan West Bengal and Sikkim during the next 24 hours.
A short-term forecast for three days ending October 13 said that scattered rainfall activity is continue over the north-eastern States and extreme south peninsular India.
The IMD expected the monsoon is likely to resume withdrawal from the remaining parts of northwest India and some parts of east and central India during this period.
As of now, the withdrawal line is stuck across the eastern fringes of northwest and central India.
WINTER RAIN OUTLOOK
Early forecasts from the European Centre for Medium-Range Forecasts (ECMWF) suggested deficit rains for northwest India during October-November-December. But normal rains from winter monsoon (northeast monsoon) are indicated for the south peninsula.
November-December-January may set off a sustained trend for normal to excess (in isolated cases) winter rains for the north-west even as benign weather conditions are indicated for the peninsula. West-central Maharashtra, Vidarbha and Orissa are about the only exception.
December-January-February would turn out to be even better for the north-west as an extension of what is likely to be exceptionally good showers over the Middle-East, Afghanistan and Pakistan.
North coastal Andhra Pradesh, Orissa and Gangetic West Bengal are also seen gaining in tandem.
January-February-March is forecast to be slightly bad for the peninsula but the reasonably good run over the northwest is forecast to continue.
In its end-of-season report for the 2009 monsoon, the IMD said that for the country as a whole, the rainfall was 77 per cent of its long period average (LPA).
Seasonal rainfall was 64 per cent of its LPA over north-west India; 80 per cent over central India; 96 per cent over the south peninsula and 73 per cent of its LPA over the north-east.
Monthly rainfall was 53 per cent of LPA in June; 96 per cent in July; 73 per cent in August; and 79 per cent in September.
Like the last two years, there has been a delay in the withdrawal of monsoon due to rainfall over north India associated with the mid-latitude westerly activities (western disturbances).
The withdrawal from west Rajasthan started only on September 25, amounting to a delay of more than three weeks. The normal date of withdrawal from extreme western parts of Rajasthan is September 1.
Subsequently, the system has withdrawn from most parts of the north-western states and from the northern parts of Gujarat by September 28, the IMD said.
The operational forecast for monsoon onset over Kerala was correct, which is the fifth consecutive correct forecast for this event since issuing this forecast started in 2005.
The long range forecast for rainfall over the country as a whole and over four homogeneous regions except south peninsula have not been accurate, the IMD said.
The forecast for August rainfall over the country as a whole also was not accurate. All these amounted to a case of overestimation of the eventual rains that fell on ground.
However, the forecast for seasonal rainfall over south peninsula and that for July rainfall over the country as a whole were more or less on target.