NE monsoon in weak phase, but not over yet

Outlook for cyclones to the South of the Equator across the South Pacific and around the Australian region in the Southern Hemisphere may indicate that the North-East monsoon over South Peninsula is beginning to end its run, but model forecasts continue to suggest that the Bay of Bengal has not heard its last hurrah yet.

These models pin their hopes on yet another easterly wave consolidating along the Sri Lankan and Tamil Nadu latitudes immediately after mid-December, translating into light showers initially before getting better organised as heavier rain over both Sri Lanka and Tamil Nadu from around December 18.

The India Meteorological Department (IMD) said on Wednesday that cyclonic circulations had been persisting from overnight in vanguard positions to either side of the Peninsula, both over the Arabian Sea and the Bay of Bengal. But the same afternoon, the latter system had moved away from the Bay and become inconsequential.

Australian monsoon

Projected return of rains to the Bay is despite indications that a monsoon trough is getting formed over waters between Indonesia and the coast of North-West Australia around the Equator and to its South. This is normally taken as a signal that the North-East monsoon is preparing to leave the Bay as well as the Northern Hemisphere.

The Climate Prediction Centre of the US National Weather Service said that the passage of a monsoon-modulating MJO wave had aided the development of multiple tropical cyclones in the Indian Ocean basin since late November, the latest of which was ‘Burevi’ in the Bay of Bengal that made landfall on the East Coast of Sri Lanka and eventually dissipated across the Gulf of Mannar.

Weak Australian monsoon

The Australian Bureau of Meteorology (BoM) qualified the observations saying that the north-westerly monsoonal winds around a related trough are weak, and are confined to a small region over the waters. A monsoon trough is typically a favourable region for the development of tropical lows and tropical cyclones.

Its formation is associated with a pulse of the MJO that exited the Bay of Bengal and moved further to the East, in combination with other tropical atmospheric waves. These short-term climate influences are conducive to widespread rainfall and the development of monsoonal conditions over North Australia, the BoM said.