The Hindu Business Line : Build-up for northeast monsoon apace

Thiruvananthapuram, Oct 9 The rain activity in east and northeast India has reduced in intensity in what is considered a slow but sure build-up for monsoon transition from southwest to northeast.

The Centre for Ocean-Land-Atmosphere Studies based in the US says that the rain belt will become increasingly insignificant over east India and hitch a ride on the Inter Tropical Convergence Zone (ITCZ) to jump south.

The ITCZ is a seasonally migrating global band of low pressure that tracks the movement of the sun into both the hemispheres and crucially decides the fate of the prevailing monsoon – southwest during summer and northeast during winter.

The ascending motion of air complete with evaporation and condensation of the seawaters provides the fertile ground for weather-driving tropical systems to spin up over the peninsular seas.

TURNING DIRECTION

The WXMAP model of the US Navy’s Fleet Numerical Meteorology and Oceanography Centre says that the low-level winds will start turning easterly-to-northeasterly over extreme south peninsula from Friday morning. The pattern will establish to the north along the Tamil Nadu coast and across the peninsula into the Arabian Sea in phases.

Meanwhile, lingering circulations from the southwest monsoon are emptying whatever available residual moisture they hold through thunderstorm activity over parts of the southern peninsula.

This is forecast to continue till such time as the winds turn direction, as per predictions by international models. This may happen decisively from October 13, according to the Global Forecast Model (GFS) of the US National Weather Services.

The European Centre for Medium-Range Weather Forecasts sees the West Indian Ocean and adjoining southwest Arabian Sea witnessing some storm activity during the early stages of what could be the northeast monsoon, 2008.

But the Paul Roundy model assesses that both the peninsular seas may be priming to see some unsettled weather during the weeks ahead. The Climate Prediction Centre of the US National Weather Services has already put the Bay of Bengal under watch in this context.

WESTERLY TROUGH

The arrival of a westerly trough around mid-October will be watched with interest, especially for implications for build-up in the Bay. It is shown to squeeze the monsoon easterlies to be concentrated over extreme south peninsula where they would be wringed of their moisture.

The resulting rain cover will progress westward from the southeast Tamil Nadu coast into the interior and further west into adjoining Kerala.

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