Vanakkam! It’s not time yet time to write an epitaph for the 2019 North-East monsoon, with even the India Meteorological Department (IMD) expecting the season to surprise weather watchers one more time. An extended weather forecast valid until December 18 has said that the South Bay of Bengal (around Sri Lanka and adjoining South Tamil Nadu) could throw up a low-pressure area or a depression during the coming week (December 12 to 18), though the probability of this happening is low.

The IMD's outlook for the southern parts of the country for the week is normal to above-normal rainfall as a weather-friendly positive phase of the Indian Ocean Dipole (where the western basin ocean warms up anomalously relative to the eastern basin) continues to rule the roost into December.

The expected low-pressure area/depression should be triggered by yet another peak in the seemingly endless storm activity in the upstream West Pacific/South China Sea to further East.

Cyclone number 9 ahead?

The US National Centers for Environmental Prediction-Global Ensemble Forecast System (NCEP-GEFS) model, too, has been hinting at development of a weather disturbance in the region in the form of an easterly wave that could likely go on to become a depression (or even an elusive ninth cyclone of the season) in the Arabian Sea and likely headed West-South-West towards the Somalian coast in East Africa.

Now, this would bear some watching! Otherwise, the weather would be most active in North and North-West India with a western disturbance, corollary to the easterly wave to the North from an opposite direction, setting up snow and thundershowers to warm up the region.

MJO influence

The IMD outlook is premised on the ground that the Madden Julian Oscillation (MJO) wave, the West to East moving moisture and convection band that periodically passes over the Indian Ocean, may have extended its stay over the Arabian Sea and the Bay of Bengal before getting active over the Maritime Continent (Indonesia, et al), though its amplitude would be less than the previous week.

This would favour enhancement of convective activity over the Arabian Sea and Bay of Bengal until December 18. MJO waves have been instrumental in the setting up of monsoon onsets, low-pressure areas/depressions or even cyclones as already evidenced during this season.

The rainfall data compiled by the IMD bears adequate testimony; +25 per cent above the long-period average (LPA) for the South Peninsula and +8 per cent for Tamil Nadu and Puducherry for the season as a whole till date (October 1 to December 4). But these figures, for the week November 28 to December 4, have been stupendous at +165 per cent above the LPA for the country as a whole; +238 per cent for the South Peninsula; and +323 per cent for Tamil Nadu and Puducherry!

Chennai: 50 per cent chance of rain!

On that note, let's look at the weather forecast for Chennai and Tamil Nadu this Tuesday. Rain maps show isolated thunderstorms active to the North-East of Chennai (in the Bay of Bengal, off the South Andhra Pradesh coast) and over Srikalahasti; to the North of Thiruvethipuram; between Polur and Thiruvannamalai; the Rasipuram-Vennathur-Tiruchengode belt; and a stream of rainy weather piping in from Puttalam in Sri Lanka across the Gulf of Mannar into Tirunelveli.

Given that the winds are northerly to north-easterly over Chennai, international weather models expect the thunderstorms off the South Andhra Pradesh coast to move in a West-South-West track, set up overcast conditions and hit Chennai with thundershowers during the day with an estimated 50 per cent chance! The temperature may peak to 29 degrees Celsius and winds should be north-easterly into the day at 15-25 km/h.

Chennai International Airport (MAA/VOMM) reported foggy conditions at 9.15 am, with the temperature at 27 degrees Celsius and calm (nil winds) with an average delay of five minutes in arrivals (reducing tendency) and eight minutes in departures (increasing tendency). Elsewhere, it would be partly cloudy over Puducherry; Salem; Tiruchirappalli; and Madurai; mostly sunny in Coimbatore; and mostly cloudy but with only a 20 per cent chance of rain in Thoothukudi.

Meanwhile, here’s a review of what social media had to say on the weather:

 

 

 

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