The Hindu Business Line : ‘Low’ ramps up to just below cyclone strength

Thiruvananthapuram, Sept 16Monday’s ‘low’ over the north Bay of Bengal became well-marked the same evening, intensified into a depression on Tuesday morning and further into a deep depression (one notch below tropical cyclone).

The system was bracing to cross the Orissa coast near Chandbali, the build-up having earlier prompted the US Navy’s Joint Typhoon Warning Centre to issue a tropical cyclone alert. The India Meteorological Department too expected the system to intensify further before crossing land.

Widespread rainfall with scattered heavy to very heavy falls and isolated extremely heavy falls have been forecast over Orissa during the next two days. Fairly widespread rainfall with isolated heavy to very heavy falls is likely over north coastal Andhra Pradesh and Chhattisgarh. Fairly widespread rainfall with isolated heavy fall is likely over Gangetic West Bengal and Jharkhand as well.

The other weather-maker, an upper air cyclonic circulation over Gujarat, too persisted from overnight. Under its influence, fairly widespread rainfall activity with isolated heavy to very heavy falls is likely over north Konkan and Gujarat over the next three days.

PROXIMITY TO LAND

Squally winds speed reaching 55-65 km/h are likely along and off Orissa and West Bengal coast during next 24 hours. Sea conditions are very rough to high along and off these coasts. Fishermen are advised not to venture into the sea.

Dr Akhilesh Gupta, Senior Adviser to the Department of Science and Technology, observed that proximity to land may not allow the deep depression to intensify as a cyclone. He expected it to wash ashore by Wednesday and move west-northwest.

Coastal Andhra Pradesh, Chhattisgarh and Madhya Pradesh are in line to get hammered as the system waded into the interior, weakening to some extent in the process. It would later be accosted by a western disturbance of moderate strength over northwest, halting its further progress.

This interaction will typically cause heavy to very heavy precipitation over northwest India and adjoining central and east India. Uttar Pradesh and Uttaranchal are expected to come in for heavy battering from this late-season burst of monsoon rains.

Parts of Rajasthan (save the extreme west), entire Punjab, Haryana and Delhi are also expected to get good rainfall. Indications are that the monsoon trough would retreat to the Himalayan foothills after the session gets over with to bring weak monsoon conditions.

FOLLOW-UP SYSTEM

The weakening flows over the Arabian Sea and the Bay should lead to this denouement, according to Dr Gupta, although the European Centre for Medium-Range Weather Forecasts has maintained its outlook for another ‘low’ to spin up over the Bay early next week.

Two successive rain-making systems are normally separated by a gap of seven to 10 days, since the pelting rains would have cooled down the sea-surface. Lower sea-surface temperatures (SSTs) cap the formation of systems, but the month of September could prove an exception.

This is because tropical seas all around the globe are the warmest during this month and host powerful systems whose remnants can travel to adjoining seas where they grow as ‘low’s.

This is unlike in July when the weather is driven by ‘in-situ’ (of local genesis) systems in the seas.

September is also the month when the monsoon withdraws from the landmass under the influence of a huge anti-cyclonic circulation pushing its way from the northwest border.

This leads to weakening of the monsoon flows, but freak systems taking shape in the Bay can rally them overnight to bring back monsoon conditions over land.

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