Erstwhile super cyclone Amphan, which crossed the West Bengal-Bangladesh coast Wednesday evening/night as a very severe cyclone, retained cyclonic strength even after 15 hours into Thursday morning. India Meteorological Department (IMD) located the system to 270 km north-north-east of Kolkata; 150 km south of Dhubri; and 110 km south-south-east of Rangpur (Bangladesh).
The IMD had expected the system to weaken as a deep depression in the morning itself while moving to the north-north-east, and further into a depression in the afternoon. The rugged terrain of North-East should have wrestled the system into submission, but there was still a lot going for it, thanks mainly to the moisture supply from a warm north-east Bay of Bengal.
Heavy rain for North-East
Despite the very heavy rain that it brought forth, sea-surface temperatures ranged from 30 to 31 degrees Celsius closer to the Myanmar coast from where the remnant Amphan was sourcing moisture. It allowed the cyclone to build clouds around, and keep itself more or less in shape. The IMD said in a noon bulletin on Thursday that it expected it to wind down as a deep depression in three hours’ time.
Amphan could trigger heavy to very heavy rainfall with extremely heavy falls at isolated places over the western districts of Assam and Meghalaya; heavy to very heavy rainfall at isolated places over Arunachal Pradesh; and heavy rainfall at isolated places over the hills of West Bengal, Sikkim, Nagaland, Manipur, Mizoram and Tripura until Friday. Squally winds (speeds reaching 50-60 km/hr and gusting to 70 km/hr) may prevail over West Assam and Meghalaya into this evening before easing.
Circulation off Kerala coast
Meanwhile, a cyclonic circulation has sprung up over the South-East Arabian Sea off the Kerala coast, which has been pulling in moisture-laden south-westerly winds towards the coast. It set up monsoon-like conditions over South Kerala with a steady drizzle right from Thursday morning and cloudy conditions. This came as a surprise since Amphan’s passing was expected to lead to shift in the direction of winds and higher temperatures.
The circulation may not last long, likely breaking down as early as on Friday, as the Arabian Sea breeds an unfriendly high-pressure region to its north-west. This will let in drier north-westerlies into Kerala until May 30, when, as per IMD projections, a fresh circulation may form off the Kerala coast. Its behaviour would bear watching for implications for the impending monsoon onset. The IMD had earlier said that the seasonal rains would arrive delayed by four days around June 5, with a model error of +/- four days.
Delay in Sri Lanka?
The US Climate Prediction Centre is of the view that a regime of rain may start building over the south-east Arabian Sea during May 27-June 2, but not quite precipitating the classical monsoon onset over Kerala. An indication to the slight lag in the sequence may be available from projections from Sri Lanka to the immediate South.
The Sri Lanka Meteorological Department expects the seasonal rains to consolidate from May 27 along its South and West coasts. The normal onset of monsoon over the island is May 22. Sri Lanka is the penultimate pit-stop for the monsoon before it reaches Kerala. Normally, it takes a week for the monsoon to advance from Sri Lanka to Kerala.