New Delhi: The prevailing weak monsoon pattern is likely to persist for five or six days, weather scientists said on Monday, attributing the monsoon's slow advance this year to the location of a global atmospheric disturbance called the Madden-Julian Oscillation (MJO).

The India Meteorological Department (IMD) said further advance of the monsoon was "not likely" during the next five or six days but has predicted "widespread rainfall" along the west coast, the Northeast and Bengal between June 23 and 25.

Scientists say storms from the Mediterranean region called "western disturbances" have also likely contributed to the stall in the monsoon's advance across the subcontinent.

The monsoon has covered the southern peninsular region and parts of eastern and northeastern India but is yet to move across Gujarat, Madhya Pradesh, Chattisgarh, Jharkhand, Bihar and eastern Uttar Pradesh which should have fallen under the monsoon line by June 15.

"The monsoon advances in pulses - we're now seeing a weak pattern, but expect to see movement next week," said D. Sivananda Pai, a senior scientist at the IMD Pune, who has examined how the MJO can influence the monsoon's advance over India.

The MJO is a large-scale eastward-moving atmospheric disturbance - marked by specific wind patterns - over the tropical region with a 30 to 60 day periodicity that strongly influences rainfall patterns over the regions of its influence as it circles the globe, moving at about 14kmph to 28kmph.

Two American meteorologists - Roland Madden and Paul Julian - discovered the MJO in the early 1970s while they were studying wind and pressure patterns in the tropics. They noticed regular oscillations in wind patterns between Singapore and Canton island in the west central equatorial Pacific, according to a paper on the MJO from the US National Oceanic and Atmospheric Administration. #Weather scientists have observed that the MJO's position influences the pace at which the monsoon advances across the subcontinent. Under the normal pace, the monsoon should cover the entire country in about 45 days - by July 15 - from the normal onset date of June 1.

"An active MJO over the equatorial Indian ocean, adjoining the Arabian Sea, or the Bay of Bengal is favourable for the monsoon's advance," said Mrutyunjaya Mohapatra, deputy director general at the IMD in New Delhi. But the MJO is currently active over central and eastern Africa.

Weather simulations suggest that the MJO will re-emerge over the equatorial Indian ocean in about five or six days, activating the monsoon's further advance, scientists said.

"This will seed the next pulse of the monsoon's advance - we expect this to start around June 25 and last for two weeks or longer, perhaps up to July 15," said Madhavan Rajeevan, a senior atmospheric scientist and the secretary in the Union earth sciences ministry.

But scientists point out that western disturbances - storms originating in the Mediterranean region and moving over the northern subcontinent, bringing thunderstorms - also have the potential to stall the monsoon's advance. Northwestern India has experienced such storms over the past week.

Senior IMD scientists say the monsoon had advanced over Kerala on May 30 and moved at its expected pace until between June 12 to 15 when the circulation pattern weakened.

Under a normal advance, the monsoon should have covered central India, Chattisgarh, Jharkhand and Bihar by June 15. But the monsoon's northern limit on Monday passed through Mumbai, Ahmednagar, Amravati, Titlagarh, Cuttack, Midnapore, Goalpara and Bagdogra.

Documented weather records suggest that the monsoon can cover the entire country up to about two weeks ahead or after the normal date of July 15.