As expected, gains from a variously successful North-East monsoon for Tamil Nadu and Kerala have extended into the first week of the New Year as moist easterlies set up a steady stream into the southern parts speeding through the Palk Strait and Gulf of Mannar before heading apparently with a purpose into the Laccadive Sea and adjoining South-East Arabian Sea/Lakshadweep, culminating in the formation of helpful troughs/circulations.
Unusual low pops up
The turn of the year also witnessed the formation of an unusual low-pressure area over the South-East Arabian Sea that intensified a round. Later, it weakened into a cyclonic circulation and hovered over the area for sometime, setting up sporadic rain accompanied by lightning and thunderstorms over parts of Kerala and Tamil Nadu, prompting coloured alerts (yellow/orange) from India Meteorological Department (IMD) about the possibility of moderate to heavy rain.
More rain for South Peninsula
On Monday, the IMD predicted light to moderate rain for Tamil Nadu, Puducherry & Karaikal, Kerala and Lakshadweep for next 4-5 days. Isolated heavy rainfall is likely over Tamil Nadu, Puducherry & Karaikal for three days until Wednesday. Squally weather with wind speeds of 40-45 km/hr gusting to 55 km/hr may prevail over along and off the Tamil Nadu-Puducherry coasts, adjoining South-West Bay, the Gulf of Mannar and adjoining Comorin area. Fishermen are advised not to venture into these areas. The 24 hours ending Monday morning witnessed heavy to extremely heavy rain over many parts of Tamil Nadu, especially to the South and Central parts of the state. Stations recording above 20 cm rain during this phase included Sirkali (24); Chidambaram (23); Velankanni (22); Tiruvarur and Nagapattinam (21 each), the IMD said. The immediate cause has been a trough that lies extended from South of Sri Lanka to the West-Central Bay off South Andhra Pradesh. This line of lower pressure is attracting weather-hungry easterlies blowing perpendicular across the Bay.
Huge rain gains
The first week of the New Year (January 1 to 7) saw the South Peninsula broke out of the pack to witness a record-breaking cumulative rainfall of +181 per cent above normal. This is despite deficient/scanty or even no rain recorded in Telangana (-100 per cent); Coastal Andhra Pradesh & Yanam (-99 per cent); Rayalaseema (-82 per cent); and Andaman & Nicobar Islands (-50 per cent) from January 1 to 7. Elsewhere, recorded surpluses ranged from +4,487 per cent in Coastal Karnataka; +3,383 per cent in Lakshadweep; +1,989 per cent in Kerala & Mahe and +1,338 per cent in South Interior Karnataka, though comparably much lower at +161 per cent in Tamil Nadu, Puducherry & Karaikal and +82 per cent in North Interior Karnataka.
Shortfall towards North
In comparison, three other homogenous geographic areas of East and North-East India (-81 per cent) and North-West India (-91 per cent) have been in deficit while Central India was above-normal at +11 per cent. West Madhya Pradesh (+235 per cent); East Madhya Pradesh (+101 per cent); and Konkan & Goa (+25 per cent) recorded large surpluses, which saved the blushes for Central India. Movement of western disturbances, a low-pressure area/trough over the Arabian Sea, and opposing easterlies from the Bay conspired to set up productive interactions resulting in sporadic rain along the West Coast and parts of Central India.
More rain forecast
US models suggest light to moderate rain may continue with localised peaks (especially over Kerala, Coastal and Interior Karnataka and adjoining parts of Tamil Nadu as well as Goa) for another week, almost in line with the IMD outlook. The European Centre for Medium-Range Weather Forecasts (ECMWF) sees enhanced prospects of rain/thundershowers for the South Indian Peninsula at least until January 17. Some of the heaviest falls may be recorded over North Coastal Tamil Nadu region around Chennai and adjoining interior with a narrow spike showing up over the South (Tirunelveli-Tenkasi belt). This is at variance with the US models which point to the possibility of the heavier rain falling over areas further to the West.