KOLKATA, July 11 — A forecast for July 12, 2026, indicates that the city of Kolkata will experience a relatively mild actual air temperature of 28°C. According to meteorological data, the expected relative humidity stands at 95%, a level that significantly alters how that temperature is experienced by the human body. The heat index, a metric formally developed by researcher Robert G.
Steadman in 1979, provides a more accurate measure of thermal comfort than air temperature alone. It is widely used by agencies such as the National Weather Service (NWS) in the United States.
The index combines air temperature and relative humidity to calculate the “apparent temperature”—what the weather actually feels like. For Kolkata on July 12, the combination of 28°C and 95% humidity yields a heat index of 34°C. Officials note that this figure, while elevated, remains below the threshold at which the NWS typically issues formal heat advisories.
The NWS, according to its established protocols, issues such advisories when the heat index is forecast to exceed 40.6°C (105°F) for at least two consecutive days. The underlying mechanism is a matter of human physiology.
At 95% humidity, the air is nearly saturated with moisture. This saturation makes the body’s primary cooling system—the evaporation of sweat from the skin—highly inefficient. When sweat cannot readily evaporate, the body struggles to dissipate heat, which increases the risk of heat-related illnesses.
The account indicates that these risks include heat exhaustion and, in more severe cases, heat stroke. While Kolkata’s projected heat index of 34°C does not approach the advisory threshold, the combination of moderate heat with extreme humidity still places a strain on the body, particularly for vulnerable populations such as the elderly or those engaged in outdoor labour.
Regional Context and the Steadman Scale
The Steadman model, now standard in many national meteorological services, was a significant departure from earlier, simpler measures of heat. By factoring in humidity, it accounts for the fact that a hot, dry day is often more bearable than a cooler, humid one. For residents of South Asia, where monsoon conditions frequently produce the kind of high-humidity environment forecast for Kolkata, this distinction is not merely academic.
State and international reports have long documented that the region’s heat-related health burdens are often underestimated when only the raw temperature is reported. The heat index provides a more realistic picture of the stress placed on the cardiovascular and respiratory systems.
What to Watch
Looking ahead, the forecast for July 12 remains below the NWS advisory level. However, the broader pattern of humidity in the region bears watching. As the monsoon season continues, similar conditions—moderate temperatures paired with near-saturation humidity—could recur.
Whether local authorities in Kolkata or elsewhere in West Bengal issue their own advisories based on local thresholds remains to be seen, but the underlying physiological risks are well-established in the scientific literature.
Sources
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