Mumbai heatwave alert: Health advisory issued as temperatures reach 38 degrees and AQI worsens

Mumbai is accustomed to humid October afternoons, but the city’s latest spell of unusually high temperatures has brought the heat firmly back into focus. 

With the mercury touching 37.6°C on Thursday and 38°C on Friday, the India Meteorological Department (IMD) has issued its first heatwave warning of the season for Mumbai and its suburbs.

The warning comes days after the southwest monsoon was officially withdrawn from the city on October 3, marking the transition to the post-monsoon season. Instead of a gradual easing into cooler weather, however, Mumbaikars are facing sweltering afternoons, high humidity and concerns over worsening air quality.

According to weather observations, Mumbai recorded a maximum temperature of 35.4°C on Wednesday, followed by 37.6°C on Thursday. The Santacruz observatory’s Thursday reading made it the hottest October day in eight years, with the station last recording a higher temperature of 38°C on October 28, 2018. The Colaba observatory, meanwhile, recorded 37.4°C.

The mercury is expected to touch 38°C on Friday, before easing to around 36°C on Saturday. Although the forecast indicates a gradual dip in temperatures over the following days, the immediate concern remains the intensity of the heat and its effects on people going about their daily routines.

The current spell is linked to a combination of atmospheric conditions that are preventing the city from cooling down as it normally would.

A prevailing anticyclonic circulation has contributed to subsidence, or the downward movement of air, which can suppress cloud formation and favour warmer conditions, as per the IMD. The delayed onset of the sea breeze is another important factor. Mumbai’s sea breeze plays a crucial role in bringing temperatures down, particularly during the afternoon. When this cooling mechanism is delayed, heat can persist for longer over the city.

The result is a combination of high daytime temperatures and humidity that can make outdoor conditions particularly uncomfortable.

The IMD’s heatwave warning signals the need for caution, particularly among people who must work outdoors, commuters, older adults, children and those with underlying health conditions. Heat exposure can cause dehydration, exhaustion and, in severe cases, heatstroke.

The rising mercury is also coinciding with a deterioration in Mumbai’s air quality, adding another layer to the city’s environmental concerns.

The city’s PM10 air quality index (AQI) reading stood at 120 on Thursday, placing it in the moderate category, compared with 91 on Wednesday. Monitoring stations recorded higher readings in several neighbourhoods, including Worli at 163, Deonar at 154, Colaba at 151 and Bandra-Kurla Complex at 130.

Experts have cautioned that the combination of heat, stagnant atmospheric conditions and limited circulation can influence the accumulation of pollutants. 

For people with asthma and other respiratory conditions, worsening air quality can add to the discomfort of hot weather. The combination underlines the importance of monitoring both temperature and pollution levels rather than treating them as separate concerns.

Doctors have advised residents to take the heat warning seriously and avoid unnecessary exposure during the hottest part of the day.

"People should drink water regularly, even before they feel thirsty, and carry oral rehydration solution or another suitable hydrating drink when required. Wearing loose, light-coloured cotton clothing, using an umbrella or hat outdoors and taking breaks in cool or shaded places can help reduce heat exposure. Anyone experiencing dizziness, unusual fatigue, headache, nausea or weakness should move to a cooler place and seek medical assistance if symptoms persist or worsen," says Dr Sarla Shah, a Mumbai based family physician.

Outdoor activity should be limited, where possible, between noon and 3 pm. People should also avoid strenuous exercise during peak heat and never leave children or pets inside parked vehicles.

While temperatures are expected to ease over the coming days, the current spell is a reminder that October can bring significant heat stress to Mumbai even after the monsoon has withdrawn.