For the first time in five years, Coimbatore has experienced a winter with average night temperatures returning to their long-term normal level. Data reveals that the city's average night temperature this winter season settled at 19.4 degrees Celsius, a figure considered standard based on three decades of climatic records.
The Return of the Nip in the Air
The period from 2021 to 2024 saw a gradual increase in nighttime temperatures during winter, deviating from the established norm. However, December 2025 brought a significant change, with residents experiencing distinctly chilly weather between 11 PM and 5 AM. According to N K Sathyamoorthy, professor and head of the Agro Climate Research Centre at Tamil Nadu Agricultural University (TNAU), the normal winter night temperature of 19.4°C is calculated using data from the last 30 years.
"Since 2021, the winter temperature has been above normal," Sathyamoorthy stated. He added that the mercury dipped to a low of 14.5°C on two occasions in December 2025, which is within the expected range. For context, the region recorded a much lower 12°C back in 1990.
The Scientific Driver: Madden-Julian Oscillation
Explaining the meteorological reasons behind the temperature drop, Coimbatore weather expert Santhosh Krishnan pointed to the influence of the Madden-Julian Oscillation (MJO). The MJO is a major intraseasonal climate pattern in the tropical atmosphere, characterised by an eastward-moving pulse of clouds, rainfall, winds, and pressure across eight defined phases.
"Phases 1-3 generally shift to the Indian Ocean, while phases 6-8 reach the Western Pacific and beyond," Krishnan explained. "The higher the phase number, the stronger the winter. Currently, the Indian Ocean region is under phases 6-7, leading to wind sinking and high pressure. This results in strong cold winds descending from the polar regions towards the Himalayas."
He further noted that the absence of cloud cover aided the cooling. The weatherman predicted that temperatures are likely to decrease again only by late January, as the MJO shifts to phases 2-3, bringing moisture back to the region.
Health and Agricultural Impacts
The sudden and prolonged chill has had tangible effects on the city's residents and its hinterlands. A retired government doctor from Coimbatore reported a spike in weather-related ailments.
"Many people have complained of sinus issues, wheezing, cold, and flu due to the sudden drop," he said. He highlighted that about 50% of fever cases arriving at clinics now present with a prolonged cough. While winter coughs and colds typically last a week, this season has seen symptoms persisting for three weeks or more for some patients. Doctors expect relief only when temperatures rise.
Agriculture has also felt the bite of the cold. Farmer R Periyasamy from near Thondamuthur reported delays in crop yield and harvesting due to the low temperatures.
"Both extremes, hot and cold, impact the plants' flowering stage," Periyasamy said. "Even banana stems are not sprouting properly this time. I have planted cauliflower on four acres, which is also impacted by the current winter conditions." The dip, while a return to climatic normalcy, underscores the delicate balance between weather patterns and daily life.
