N-E monsoon ready to exit as parent cloud band dips to Southern Hemisphere 

The India Meteorological Department (IMD) has assessed that conditions are becoming favourable for cessation of the North-East monsoon rain over Tamil Nadu, Puducherry & Karaikal, Kerala & Mahe, and adjoining areas of Coastal Andhra Pradesh & Yanam, Rayalaseema and South Interior Karnataka around Monday, right after Makar Sankranti. 

It also more or less coincides with the conventional end of the peak winter-time fog season over North-West India, Central India, and East and North-East India. The peak season lasts almost a month from December 15 to January 15. On Friday morning, the IMD forecast dense to very dense fog to prevail over these regions from West to East over the next four to five days. A couple of moisture-laden western disturbances are expected to call in over the region during this period.

• Also read: South Peninsula makes smart rain gains as year turns

ITCZ heads southwards

Meanwhile, satellite maps focussing on the tropics showed the Inter Tropical Convergence Zone (ITCZ), which houses the monsoon trough and tracks the movement of the Sun across the tropics, as having exited the North Indian Ocean region (the Bay of Bengal and the Arabian Sea) and transiting to the Southern Hemisphere. It will soon trigger the next big monsoon mainly over Australia. It’s from here that the ITCZ swings back to the Northern Hemisphere to set up India’s South-West monsoon by June.

The ITCZ is a belt of low pressure encircling the Earth found generally near the equator where trade winds from the Northern and Southern Hemispheres meet. It is characterised by convective activity which generates vigorous thunderstorms over large contiguous areas and sets up monsoon onsets over disparate regions, apart from tropical disturbances including cyclones.

Tracks Sun’s movement

As mentioned already, the position of the ITCZ varies seasonally because it follows the Sun; it moves to the North during the Northern Hemisphere summer (bringing the monsoon to India, among other countries) and to the Southern Hemisphere during the Northern Hemisphere winter. In this manner, the ITCZ is responsible for the wet and dry seasons in the tropics.

The monsoon is due in Australia by December-end but has been delayed by close to a fortnight this year. It was held back over South India and Sri Lanka by westward moving waves/troughs bringing year-end extreme rains over the region. The Australian Bureau of Meteorology said, as of January 9, the monsoon was yet to arrive across northern Australia, its first port of call.

Heat wave over Australia

Typically, it descends over the region by December 28/29 in Darwin; the latest known date of arrival is January 25, 1973. The lack of monsoonal weather has resulted in build-up conditions across the Tropical North of the country/continent, with heatwave conditions being in some locations. The monsoon trough is lately forecast to potentially arrive by this weekend.

The Bureau has predicted the February to April rainfall is likely to be below the median for most of Northern Australia, western parts of West Australia, and parts of southern Australia. Maximum and minimum temperatures are very likely to be above the median for most of Australia during this period. They are at least two times more likely than normal to be unusually high for much of Australia, in the backdrop of strong El Niño conditions prevailing over the Equatorial Pacific to the North and East. 

COMMENT NOW