Winter continues to sweat on its journey to Calcutta this year, pushing up December temperatures to their highest mark in a decade.

The discomfort index soared on a cloudy Thursday as the minimum temperature shot up to 20.6 degrees Celsius, six points above normal and the highest for any December day in 10 years.

“The previous highest minimum temperature was 20.1 degrees Celsius, coincidentally recorded on December 11 two years ago,” confirmed G.C. Debnath, the director of the weather section at the Regional Meteorological Centre in Alipore.

But weather scientists insisted it was an aberration rather than a trend. “Sometimes we have cooler days in December, sometimes warmer,” said B. Bandopadhyay, the deputy director general of the India Meteorological Department (IMD) in New Delhi.

“We need to analyse decades of data to identify long-term trends,” he added.

Two remnants of low-pressure systems that migrated from the Mediterranean region earlier this month are said to be responsible for the unusually warm weather across eastern and northwest India.

“A western disturbance draws winds from the south that are relatively warm. But as it moves eastward, cold and dry winds from the northern latitudes move in and the temperatures drop,” Bandopadhyay said.

One such western disturbance was over Jammu and Kashmir on Thursday and another was over north Bengal.

So when will Calcutta feel a nip in the December air?

“As both disturbances move eastward, temperatures will drop. The weather should be colder by Sunday,” a Met official said.

The trajectory of the disturbance currently over Jammu and Kashmir will determine how long the cooler weather that is expected to set in by Sunday lasts in eastern India.

If the disturbance shifts southward along its eastward movement, it could get a bit warmer again and stay that way until the pattern changes.

The warm winter syndrome has not only left Calcuttans hot under the collar but made them disease-prone, too.

“Winter protects people from viruses. The warm weather over the past week has triggered diseases that usually strike only in summer and in the post-monsoon period,” said critical care specialist Subrata Maitra.

On the flip side, the incidence of “winter ailments” like arthritis has been low this December.

Doctors advocate extra caution for children under the current weather conditions. “A very high percentage of children are now suffering from mild to severe diarrhoea, which is a feature of summer and the first couple of months after monsoon,” said Apurba Ghosh, the director of the Institute of Child Health.

Paediatricians are also receiving a high number of patients with upper respiratory tract infections.

Occupancy rates of hospitals have increased since the beginning of the month, with most new patients being diagnosed with viral diseases that strike in warm weather.

“Most patients complain of sore throat, often accompanied by fever,” said Arunabha Sengupta, a senior ENT specialist at SSKM Hospital. “We had received 20 to 25 such patients a day during the same period last year. The number has increased to 50-60 this December.”

Doctors have advised people to drink plenty of fluids and avoid “sudden temperature fluctuations” like going in and out of an air-conditioned room.

“Wearing warm clothes when not required can cause harm, too. The person will sweat if he/she is wearing too much and that can lead to cold and cough,” a doctor said.