India Meteorological Department (IMD) has on Tuesday hinted at the formation of a cyclonic storm in the Bay of Bengal by this weekend or early next week, after a low-pressure area in the making intensifies in phases, taking advantage of the helpful atmospheric and oceanic features. The low-pressure are itself is likely to form over the South-East and adjoining East-Central Bay around the Andaman and Nicobar Islands in the next two days. It is likely to concentrate into a depression by Saturday morning and undergo another round of intensification as a deep depression, before going on to become a cyclone over the West-Central Bay from where the coast of Andhra Pradesh would be the closest on view.

No consensus on landfall

The IMD has not taken a call on where the prospective cyclone is headed, of which even the global models have not been able to arrive at a consensus. They tend to take the storm towards an arc along the entire East Coast from Andhra Pradesh to Odisha to West Bengal. The track of movement would depend on the location of the seasonal anticyclone over North-West India, packing helpful easterlies to its southern flanks as also any incoming western disturbance which can swing the cyclone away to the Odisha, West Bengal or even Bangladesh coasts.

The US National Centres of Environmental Prediction/Global Forecast System take the storm away to Odisha, while the Canadian Met Centre guides it towards Myanmar/Bangladesh; the Japanese Meteorological Agency and the US Navy Global Environmental Model point towards Tamil Nadu/Andhra Pradesh as a landfall area; and the UK Met Office, at Odisha. An early outlook from the IMD’s numerical models suggests the cyclone may be headed towards the Andhra Pradesh coast for landfall by Diwali day (Monday), subject to plotting/ verification on a day-to-day basis.

Ocean warmth spreads

On Tuesday afternoon, the above-normal warmth of the ocean waters to the North of the Bay (up to 30 degrees Celsius) had spread to the West-Central parts where the cyclone is expected to form. Wind shear values, or the change of wind speed and direction with height, are favourable at the genesis of the ‘low’, but show a tendency to increase slightly when it gathers strength to become a cyclone. This will have the effect of capping the system’s strength, since higher values of wind shear (such as during peak monsoon) may not allow the storm to build mass and intensity beyond a point.

Large rain surpluses so far

The ongoing monsoon transition period (South-West to North-East) from October 1 to 17 has generated a large surplus of 82 per cent until Monday evening, with North-West India topping the chart with a massive +277 per cent, followed at quite some distance by Central India (+92 per cent); the South Peninsula (+52 per cent); and East and North-East India (+41 per cent). Uttar Pradesh, which faced big rain deficits for most part of the prevailing South-West monsoon, received the highest amount of rain during this period. The meteorological subdivision of West Uttar Pradesh was pounded with a huge surplus of +703 per cent, while East Uttar Pradesh recorded +402 per cent, India Meteorological Department (IMD) statistics revealed.

Other big surpluses

The next biggest gains occurred over Haryana, Chandigarh and Delhi (+391 per cent), followed by snow and avalanche-hit Uttarakhand at +355 per cent. Over adjoining Central India, West Madhya Pradesh topped with +313 per cent, while East Madhya Pradesh received +187 per cent rainfall. The rest of the surplus rain falling across the country was in double-digits, while at least five meteorological subdivisions have returned deficits. The largest deficits are in Saurashtra and Kutch (-52 per cent) and West Rajasthan (-51 per cent), two border areas from where the South-West monsoon exited first.

Rain-deficit areas, too

Other deficit sub-divisions are Lakshadweep (-42 per cent)and Kerala and Mahe (-35 per cent) over the South Peninsula, and Nagaland-Mizoram-Manipur-Tripura (-24 per cent) over North-East India. These areas proved beyond the reach of the rain-generating western disturbances moving across North-West, or cyclonic circulations/ troughs extending from the Arabian Sea or the Bay of Bengal to the North Peninsula, Central or North-West India, either by themselves or by way of mutual interactions. The withdrawal line of the South-West monsoon has advanced to the North Peninsula and East India, which will confine rain to the South Peninsula, where the North-East monsoon is due to arrive.