The Hindu Business Line : Arabian Sea ‘low’ may ramp up to depression status

Thiruvananthapuram, Nov. 8 The northeast monsoon has continued to be vigorous over Tamil Nadu, south coastal Andhra Pradesh and Kerala while being active over Rayalaseema during the last 24 hours ending Sunday morning.

A weather update from the Chennai Met Centre said that rainfall occurred at most places over Tamil Nadu, Kerala, south coastal Andhra Pradesh and Rayalaseema and at many places over Lakshadweep and at a few places over south interior Karnataka during this period.

Isolated rainfall occurred over north interior Karnataka, north coastal Andhra Pradesh and Telangana.

More in offing

Forecast for the next two days said that rain or thundershowers are likely to occur at most places over Kerala and at many places over Tamil Nadu, Puducherry, south coastal Andhra Pradesh and Lakshadweep and at a few places over coastal and south interior Karnataka and Rayalaseema.

Isolated rain or thundershowers are likely to occur over north coastal Andhra Pradesh, Telangana and north interior Karnataka.

A warning valid for the period said that isolated heavy to very heavy rain is likely to occur over Kerala and Lakshadweep. Isolated heavy rain is also likely over Tamil Nadu, Puducherry and south coastal Andhra Pradesh.

Meanwhile, the causative well-marked ‘low’ over Kanyakumari and neighbourhood has shifted north-northwest to lie over Lakshadweep on Sunday.

India Met Department (IMD) quoted numerical weather guidance to suggest that the gather further strength to concentrate into a depression around Tuesday even while moving north-northwestward largely over the seas.

Fairly widespread to widespread rainfall with isolated heavy to very heavy falls is likely over south peninsular India during the next two days. Subsequently, the rainfall belt is likely to extend into Maharashtra and Goa and adjoining Gujarat.

IN AGREEMENT

This IMD outlook is in line with what most international models have been suggesting over the past week or so.

More supportive guidance were available on Sunday with a majority indicating that the Arabian Sea weather system may track north-northeast track along an upper-air ‘highway’ facilitated by an eastward-bound disturbance (western disturbance) dipping low into the Arabian Sea.

This westerly system is expected to cross in from the northwest border during the next two days, the IMD said.

However, a couple of the international models begged to differ, saying that the system may propel north along the west coast to head into south Gujarat or even take a westward turn off the north Konkan coast into the open waters.

All others, including the European Centre for Medium-Range Weather Forecasts (ECMWF), the precipitation forecast model of the US National Centres for Environmental Prediction (NCEP) and the Climate Prediction Centre (CPC) of the US National Weather Services, were of the view that the system may wade into the Konkan coast and spread itself out thin over west-central India.

The NCEP is forecasting up to 600 per cent above rainfall for the week ending November 15 for a whole swathe of land from coastal and north interior Karnataka, adjoining Rayalaseema and Telangana, madhya Maharashtra, Marathwada and even Vidarbha.

Facilitating role

This is being attributed to the facilitating role of the western disturbance, which, while dipping low over the Arabian Sea, would set up a large trough encompassing most of the southeast and central Arabian Sea, peninsular India and southwest Bay of Bengal.

This pan-peninsular trough would wrap itself around the Arabian Sea depression and help wheel it along the upper air highway from over the coastal Karnataka-Konkan coast into the mainland where it would drop its contents.

Meanwhile, the CPC has hinted at the possibility of tropical cyclone development over the southwest Bay around Sri Lanka during November 10 to 16 under the combined impact of the eastward movement of the enhanced precipitation zone from west to east and above-average sea-surface temperatures over equatorial Indian Ocean.

This is in turn attributed to the strong MJO (Madden-Julian Oscillation) wave over the equatorial Indian Ocean, a periodical upper air wave transiting from the west to the east and which magnifies weather happening under its foot print.

The alternating dry MJO wave, which indicates suppressed rainfall regime, will kick in from around November 22, and would be active December 13, according to model forecasts.

The Forecast

Strong signal of rain-generating MJO wave over peninsular seas.

Well-marked ‘low’ over Arabian Sea may intensify into depression.

May cross Konkan coast and travel north-northeast to bring heavy rains over coastal and north interior Karnataka; adjoining Rayalaseema and Telengana, Madhya Maharashtra, Marathwada and Vidarbha.

Up to 600 pc above normal rains likely over these regions during week ahead.

Likely storm development in southwest Bay of Bengal basin during November 7-16, says US model.

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