The Hindu Business Line : Bay warming up as monsoon hits South-East Asia

Thiruvananthapuram April 30 The upper air cyclonic circulation over the south Andaman Sea (southeast Bay of Bengal) is tipped to descend to lower levels to set up the first pre-monsoon `low' by Tuesday.

This will happen as a result of the waxing-and-waning motion of the northward-migrating Inter Tropical Convergence Zone (ITCZ), the global band of low pressure, which tracks the movement of the Sun into the northern hemisphere.

But the evolving `low' may not impact the mainland's weather (except widespread rain for the Bay Islands) since it would move north-northeast towards Bangladesh/Myanmar as predicted by several weather models.

ONSET FEATURES

Further onward movement of the ITCZ into the south peninsular-Sri Lankan latitude triggers the onset of monsoon over the mainland, which is sometime away. The onset over the Andaman Islands, India's outpost in the territorial waters far into the southeast, precedes this by 10 to 12 days.

Meanwhile, widespread clouds revealed by satellite shots over Southeast Asia are indicative of the early phase of the monsoon setting over this region, say meteorologists. The build-up, as evidenced in the looming cloudiness, is strong, according to Dr K. J. Ramesh of the Department of Science and Technology.

ITCZ MOVES IN

A vital facilitator of the larger monsoon ensemble, the ITCZ has already moved into the Malaysian latitude. It needs to move only slightly further north to trigger the Indian monsoon.

Mr Jim Andrews of AccuWeather.com also agreed with the outlook saying that the rising observations of rain, lowered high temperatures and the widespread clouds suggest that the monsoon is setting over Southeast Asia. This is rather normal for the start of May.

According to Dr Ramesh, the next important cyclical feature to be looked forward to is the strengthening/deepening of the segment of southwesterlies concurrently prevailing over Malaysia, and its gradual migration to the northwest to impact the Bay of Bengal.

ANTI-CYCLONE FORMS

A helpful anti-cyclone has formed in the upper levels of atmosphere, which should aid the northwesterly progress of the core of winds. This is what results in the Bay of Bengal arm of the monsoon developing first. The Bay has warmed up sufficiently in anticipation of the development.

Thundershowers will henceforth become a more regular feature along the Kerala and Karnataka coasts (up to Mangalore), the latent heat of condensation from which will warm up the atmosphere further. This will in turn boost its moisture-carrying capacity, and help build the westerly flows in due course.

HEAT WAVE

Heat wave conditions continued to prevail over some parts of Rajasthan, Punjab, Haryana, Delhi, West Madhya Pradesh and Vidarbha where the day temperatures were above normal by 4- to 6 deg C.

However, possible dust storms/thunderstorms expected over the next 2-3 days might just be able to bring marginal relief to these areas. Marginal, because no dip of mercury below 40 deg C-mark is seen, said Mr J.V. Singh of the National Centre for Medium Range Weather Forecasting .

Isolated to scattered rain/thunderstorm activity will continue over east India during next 48 hours with increase thereafter. Consequently day temperatures are likely to remain below normal over the region.

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