India Met Department (IMD) has upgraded the weather outlook in the Arabian Sea to a tropical cyclone, with a preparatory well-marked low-pressure area over the East-Central basin (closer to the West Coast of India) showing signs of fresh traction. The expectation is that the well-marked 'low' would intensify into a depression by tomorrow (Thursday) - though earlier timelines for the event may have passed - and further into a depression by Friday.


After freeing itself from the clutches of a weakening western disturbance from the opposite direction that would keep pushing it closer to India's coast until Friday, the 'low' would later move away and intensify as a cyclone heading likely for Oman.  The IMD's outlook for a tropical cyclone brewing in the Arabian Sea is being supported by global weather models, led by the Climate Prediction Centre (CPC) of the US National Weather Service.

Pointing to a 'broad area of low pressure over the Arabian Sea,' the CPC said GFS (Global Forecast System) and the ECMWF (European Centre for Medium-range Forecasts) models are in excellent agreement that it would develop into a depression and a cyclone.


Source: Climate Prediction Centre of the US National Weather Service

It would move away from the West Coast of India while rapidly intensifying as it tracks west across the Arabian Sea. There are increasing chances that this tropical cyclone approaches Oman or Yemen early during the week October 23-November 5, the CPC said.

Based on the predicted evolution of the weather-boosting Madden-Julian Oscillation (MJO) wave, model guidance, and climatology, moderate confidence exists that another depression forms in the South-West Bay of Bengal as well, the CPC said.

According to the IMD, the well-marked 'low' lay on Wednesday afternoon over the West-Central Bay of Bengal off the Andhra Pradesh coast. It is very likely to move to the North-North-West towards the North Andhra Pradesh coast.

Rain moves north

Under the influence of the above systems, the IMD has forecast fairly widespread to widespread rainfall with isolated heavy to very heavy falls likely over Konkan, Goa, Coastal Karnataka, Odisha and Coastal Andhra Pradesh during the next two days.

Extremely heavy falls are forecast for Konkan, Goa and Coastal Karnataka on Friday, as the heavy rain belt moves away from the familiar terrain - and a typically North-East monsoon playground- of Kerala, Karnataka and Tamil Nadu, 

The sudden change in the dynamics had prompted the Met Department to withdraw the 'red alerts' declared in Kerala for today (Wednesday) and limit the 'orange alerts' after the state saw heavy to very rain on Tuesday.

The North-East monsoon was expected to fire away on the strength of the two 'engines' ('low's) but the scenario always the runs the risk of one getting undermined by the other since no two 'low's can normally coexist in a single monsoon system. 

In the instant case, the 'low' in the Bay began to redirect some of the flows from the Arabian Sea to itself and intensify, delaying the calibrated growth of its counterpart in the Arabian Sea.

Once the Bay system crosses Andhra Pradesh coast, its cousin in the Arabian Sea would be able to breathe free and intensify, even as it makes a U-turn back to the open waters where it would intensify as a cyclone.

An IMD outlook from October 28 to 30, however, said that fairly widespread to widespread rainfall may return to South India with heavy falls at isolated places over Kerala, Tamil Nadu, and Puducherry.

May return soon

It would be scattered to fairly widespread over Odisha, Chhattisgarh and Maharashtra and isolated to scattered over Madhya

Pradesh, Gujarat and North-East India.       

The CPC says the North Indian Ocean (comprising both the Arabian Sea and the Bay of Bengal) are apparently drawing strength from the periodical West to East-moving Madden-Julian Oscillation (MJO wave) from Africa to the Pacific across the Indian Ocean.

The MJO wave passes periodically from Africa to the Pacific across the Indian Ocean, represents a low-pressure band packing moisture, clouds and rainfall, and is known to boost weather under its footprint - be it monsoons, low-pressure areas, depressions or cyclones.

Already, the western basin of the Indian Ocean (and by extension the adjoining Arabian Sea) is under the influence of a monsoon-booster positive Indian Ocean Dipole (IOD), that warms up the ocean and escalates convection (cloud-building).

According to the CPC, the strong positive phase of the Indian Ocean Dipole continues to be a major factor in anomalous tropical convection and storm building across the Indian Ocean. 

Dynamical models continue to have difficulty in how much the MJO weakens as it begins to destructively interfere with the positive IOD during the next week (May 23-November 5) since it encounters cooler seas over the East North Indian Ocean (Bay of Bengal).

Based on the predicted evolution of the MJO wave, model guidance, and climatology, moderate confidence exists that another depression forms in the South-West Bay of Bengal as well, the CPC said.