In December 2023, Tamil Nadu, nestled in southern India, experienced an unprecedented onslaught of rain, triggering a sequence of unfortunate events.
This increase in rainfall was due to the active northeast monsoon (NEM) sweeping over the southern peninsula, a seasonal phenomenon known to last for about 70 days and affecting coastal Tamil Nadu and Andhra Pradesh.
December began with Chennai and neighboring regions witnessing notable downpours due to the onset of Cyclone Michaung. After a gap of almost 15 days, Tamil Nadu suffered overwhelming downpour, mainly on December 17 and 18.
This exceptional weather continued throughout the week, inundating several southern districts with extreme rainfall, resulting in the loss of 31 lives and causing widespread flooding.
Event severity
Between October and December, Tamil Nadu received 453.7 mm of rain, slightly exceeding the expected normal of 430.7 mm.
Some districts experienced rainfall almost equal to or above the annual levels predicted for the region.
According to the India Meteorological Department (IMD), the following three districts experienced significantly more rainfall.
| Districts | Seasonal rains for the period from October 1 to December 20 (2023) | ||
| Real (mm) | Normal (mm) | Departure (%) | |
| Tirunelveli | 1221.3 | 486.9 | 151 |
| Kanniyakumari | 1050.7 | 519.1 | 102 |
| Tootukudi | 809.4 | 422.9 | 91 |
The persistent damage caused the cancellation of about 15 trains and interruptions in flight operations, in addition to damage to infrastructure.
Revealing the catalysts
The IMD flagged a vigorous NEM over Tamil Nadu and its southern regions, with the The boy phenomenon that plays a fundamental role in its intensification.
He does not evenNoPart of the El Niรฑo-Southern Oscillation cycle, it involves sporadic warming of sea surface temperatures in the central and eastern tropical Pacific Ocean.
On December 16, a cyclonic circulation formed in the southwest Bay of Bengal. Gradually moving westwards, this system strongly influenced the NEM winds, which persisted across southern Tamil Nadu on 18-19 December.
Vineet Kumar Singh, a researcher at Jeju National University's Typhoon Research Center, emphasized that this circulation caused a substantial divergence in the upper atmosphere, resulting in a sharp increase in moisture-laden winds. These conditions created deep convective clouds with high rainfall rates (in the range of 60 to 70 mm/h), precipitating extreme precipitation due to the convergence of moisture-rich easterly winds.
Reflecting on historical parallels
Drawing parallels with the 2015 NEM, the occurrence of a similar event bound the intense floods in South India to the powerful El Niรฑo conditions and dominant easterly wave activity that supported the intensification of synoptic systems developing over the Bay of Bengal.
Experts believe that this current event, similar to the intense El Niรฑo events of 1982, 1997 and 2015, could be due to an extraordinary El Niรฑo occurrence.
With a view towards climate changeexpectations arise of more intense El Niรฑo episodes in the futurecombining a rise in temperatures and the appearance of El Niรฑo, amplifying the probability of extreme weather events conditions.
Challenges in prediction
The IMD red alert projected rainfall of more than 210 mm; However, Kayalpattinam in Thoothukudi district recorded a staggering 950 mm in a single day, eclipsing the district's annual average of 700 mm.
Experts highlighted that it is a relatively shallow system, which exceeds the expected intensity due to the greater humidity coming from the easterly winds.
Weather prediction models face challenges in predicting the scale of extreme rainfall events, leading to difficulties in accurately predicting outliers, in this case 950 mm of rain in one day, underscoring the need for Comprehensive satellite analysis and real-time data.
Forecast ahead
The latest IMD forecast does not predict any significant rainfall or warnings in Tamil Nadu. However, the outlook suggests the likelihood of light to moderate rain in certain parts of Tamil Nadu, Puducherry and Karaikal region till Friday due to a surge of easterly wind.
According IM D, Under the influence of a new easterly wave and the low pressure area mentioned above; Light to moderate rain at places is very likely over southern Tamil Nadu, southern Kerala and Lakshadweep from December 31, 2023 to January 4, 2024, with isolated heavy rain over Lakshadweep on January 2, 2024 .
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