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The North-East monsoon may have officially drawn to a close. Still, the South Peninsula is witnessing a heavy rain spell triggered by an easterly wave with signatures of a passing Madden-Julian Oscillation (MJO) wave and the reigning La Nina in the tropical Pacific written all over it.
The MJO wave amplifies prevailing weather over the Indian Ocean during its regular transit from East to West. At the same time, warming of the West Pacific in a La Nina phase equips easterlies from the West Pacific/South China Sea with ample moisture as they blast into the Bay of Bengal.
Active easterly wave
India Meteorological Department (IMD) pointed to a trough running from the East-Central Arabian Sea off the Karnataka coast to South Madhya Maharashtra that prompts the easterlies associated with an active easterly wave from the Bay to guide their moisture content across the South Peninsula and into the trough.
The IMD has predicted scattered to fairly widespread precipitation accompanied with thunderstorm and lightning over the South Peninsula during next 4-5 days. Isolated heavy rainfall is likely over Tamil Nadu, Puducherry, Karaikal, Kerala and Mahe on Wednesday and Saturday; and over South Interior Karnataka on Wednesday.
Rains may last until January 12
The European Centre for Medium-Range Weather Forecasts said that the rains would last variously over the South Peninsula for a week or so. Extended forecast by the IMD until January 12 said that fairly widespread to widespread rainfall/thundershowers might lash Kerala, Mahe, Tamil Nadu, Puducherry and Karaikal. Isolated to scattered rainfall/thundershowers are likely over Maharashtra, Goa, Karnataka, Andaman & Nicobar Islands and Lakshadweep.
Chennai has received heavy to very heavy rainfall during the last couple of days after being swamped by the easterlies. Nungambakkam recorded 6.3 cm of rain during the 24 hours ending on Tuesday morning, only to be greeted by even heavier rain during the day.
Chennai sees a high post-2002
Chennai Airport observatory saw 4.5 cm during the same period, according to private forecaster Skymet Weather. The monthly total for Nungambakkam reached 6.8 cm till date (January 5), the highest rainfall recorded since January 2002 when the capital city clocked 9.1 cm.
The normal rainfall for Chennai for January is a mere 2.6 cm, and the city goes nearly dry in February and March, with an average rainfall of 0.34 cm and 0.45 cm respectively. But monthly normal escalates to double-digits in April (1.4 cm) with sporadic pre-monsoon showers.
More rain seen for Chennai
Heavy rainfall with lightning and thunderstorm is expected over the city suburbs in the next two days. Two-decade-old record of 9.1 mm in January 2002 may likely tumble in the process. A stream of easterlies is seen converging along the coast, particularly from Chennai to Karaikal.
Meanwhile, to the North-West of the country, an incoming active western disturbance parked over Afghanistan has generated a lot of weather over the hills and plains and adjoining Central India. Unseasonal rains are forecast even for Maharashtra over the next four days, especially over Madhya Maharashtra, Marathawada and Vidarbha but mainly due to what is happening over the South Peninsula, said Skymet Weather.
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