Active monsoon spell from next week as Bay hosts back-to-back ‘lows’

India Meteorological Department (IMD) has hinted at the formation of back-to-back low-pressure areas in the Bay of Bengal during the ongoing week (September 2-8) and the subsequent one (September 9-15) as a monsoon-friendly but stalled Madden-Julian Oscillation (MJO) wave has strengthened over Equatorial Indian Ocean and resumes its eastward journey across the Bay into the Maritime Continent.

The wave could start its movement with a gradual increase in amplitude from the beginning of the second week (September 9 to 15) and enter the Andaman Sea by the weekend. Packed with clouds, moisture and precipitation, it will trigger formation of low-pressure areas in the Bay.

Model consensus on ‘lows’

The first ‘low’ is expected to materialise over North and adjoining Central Bay in the next three days (around Monday) while the exact dateline for the subsequent one has not been predicted. There is wide variation in location predicted by global weather models with respect to the place of their genesis.

But there is concurrence on the window of their formation and movement towards North Andhra Pradesh-South Odisha coasts, which appear to be the favourite landfall area for them during the second half of the monsoon. The first 'low' would intensify to being well-marked before moving inland.

In view of this, the IMD has forecast isolated heavy falls over East Gujarat, Uttar Pradesh, Bihar, Rajasthan, and Haryana, Saurashtra and Kutch on Friday. Rainfall over the South Peninsula, where some areas are still in deficit, may increase from Saturday.

Rains to return to South

Overall rainfall activity is forecast to be above normal for the whole week ending Wednesday next with welcome rains indicated for parts of Central and adjoining Northwest India which account for bulk of the overall deficit of nine per cent after there were not enough rains in August.

Fairly widespread to widespread rainfall activity and isolated heavy falls is forecast over Konkan, Goa, Coastal Andhra Pradesh, Telangana and Tamil Nadu for five days and over Karnataka, Kerala, Mahe and Marathwada for four days from Saturday, and over Madhya Maharashtra from Monday to Wednesday.

Isolated heavy to very heavy falls are likely over Konkan, Goa (including Mumbai) and Madhya Maharashtra on Tuesday and Wednesday. Rainfall activity over Central India is also forecast escalate from Sunday with fairly widespread rainfall and isolated heavy falls over Chhattisgarh until Wednesday.

A similar forecast is valid for Vidarbha and East Madhya Pradesh from Monday to Wednesday and over West Madhya Pradesh from Monday to Wednesday. Scattered to widespread rainfall may continue over East India during the next 4-5 days with isolated very heavy falls over the hills of West Bengal and Sikkim for today and over Assam and Meghalaya on Tuesday and Wednesday.

Another spell for Northwest

Isolated heavy falls is likely over Odisha for six days from Friday to Wednesday. Rainfall may increase with scattered to fairly widespread rains over most parts of Northwest India with possibility of heavy rainfall over Uttarakhand and Himachal Pradesh early next week.

In forecast for the subsequent week (September 9 to 15), the IMD said that the backbone monsoon trough will stay near to its normal or even south of its normal position, which is even more favourable, during most days of the week. As already indicated, this week will see genesis of a second ‘low’.

This would likely bring a second round of rainfall over Northwest and Central India while the intensity may be reduced over the South Peninsula compared to the first week. Fairly widespread to widespread rainfall with isolated heavy falls may lash North-West and Central India during most of the days.

Overall, above-normal rainfall is indicated for this week over Northwest, Central and East India; near-normal over the Northeastern States and below-normal to near-normal over the South Peninsula.

COMMENT NOW