An unusual weather system called “mesoscale vortex” over north Mumbai and a low-pressure area in eastern Madhya Pradesh explain the record rain over Mumbai and Konkan, a senior meteorologist has said.

The weather office at Santa Cruz in north Mumbai recorded 94.4 cm of rain over the past 24 hours ? 2.5 times higher than the last record of 37.5 cm in 1974. But Colaba in the southern tip of the city registered only 7.3 cm.

This significant difference in rainfall within the city may be explained by a vortex ? a whirling mass of air and moisture that sucks everything near it towards its centre. A mesoscale, or small-scale, vortex triggered by strong winds would suck enormous moisture into the atmosphere and lead to heavy rains, said Basab Bandopadhyay, a senior scientist at the Indian Meteorological Department (IMD).

However, Bandopadhyay added, a well-marked low-pressure zone in eastern Madhya Pradesh is the cause of heavy rains across the Maharashtra and Konkan regions. It is normal for such low-pressure zones to form during the monsoon months.

Such low-pressure areas usually form in the Bay of Bengal and move westward over peninsular India. The southwest sector of such a low-pressure area usually gets plenty of rainfall, he said.

In its daily monsoon forecast issued on Wednesday, the IMD said the ongoing rainfall along the west coast is likely to continue over the next 48 hours.

Gujarat is also likely to receive increasing rain over the next two days.

G.S. Mudur