The Hindu Business Line : Monsoon onset over Kerala by May 29: IMD

The special IMD bulletin did not say anything about the onset of the Bay of Bengal arm of the monsoon that hits the North-East around the same time.

Vinson Kurian

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Thiruvananthapuram, May 14 India Meteorological Department (IMD) announced late on Wednesday evening that the southwest monsoon would break over the Kerala coast on May 29, with a model error of four days.

In its initial forecast made last month, the IMD had said the season would ring in at least a week ahead of June 1, the normal date for onset. It is likely that a series of intervening storms in the Bay of Bengal and the neighbouring South China Sea have diverted the flows, creating a lag in the progress of the upstream Arabian Sea arm.

The special IMD bulletin did not say anything about the onset of the Bay of Bengal arm of the monsoon that hits the North-East around the same time as the rains reach the Kerala coast. The strengthening and deepening of winds and widespread rainfall had helped it advance into southeast Bay of Bengal, Andaman and Nicobar Islands and north Andaman Sea on 12 May, almost eight days in advance.

STORM ALERT

Meanwhile, an alert on possible cyclone formation off Myanmar coast put out by the US Joint Typhoon Warning Centre (JTWC) prompted close scrutiny of the prevailing “low” in the Bay of Bengal.

Earlier this month that Nargis, a rare Category-4 cyclonic storm originating in the Bay, had barrelled into the Myanmar coast, accounting for tens of thousands of lives and devastating South-East Asia’s “rice bowl”.

JTWC had cited a pronounced low-level cyclonic turning of convection at the `western end of the pan-Pacific monsoon trough’ although the convection had waned more recently somewhat in response to land interaction.

POOR CHANCE

According to an India Meteorological Department (IMD) update late on Wednesday, the “low” over east-central Bay and adjoining coastal areas of Myanmar persisted. This system may become more marked during the next 24 hours but chances of its intensification into cyclonic strength were poor.

Real-time simulation runs by the multi-hazard early warning system (EWS) at the Asian Disaster Preparedness Centre (ADPC) in Bangkok too had ruled out cyclone formation. Dr Jayaraman Potty, Climatologist at the ADPC-EWS, told Business Line that told model runs did not indicate that possibility just yet.

There is a “low” over the coast of Myanmar with a central pressure of about 1000 millibars. The central pressure has to wind down to 980 millibars and average wind speeds touch 62 km/h for the system to attain `tropical cyclone’ status. Southwesterly currents are getting stronger by the day in the Bay indicating the advance of monsoon circulation.

Proximity to land surface and short stay over the waters would combine to deny the system the elbowroom to kick up high winds or compress central pressure markedly. But the JTWC seemed to lay much store by the flooded tracks of Yangon to predict system strength.

Flooded topography allows the storm to rustle up a pace that nearly matches as when it glides over sea surface. The JTWC expected minimal system degradation, given the topography and fairly quick transit over the low-lying southern Myanmar coast.

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