A common mistake on a muggy day: someone looks at the forecast, sees 34°C, and shrugs. That same 34°C with 70% humidity has a feels-like value of 48°C, well past the danger threshold for prolonged outdoor activity, according to Mausam Online’s weather glossary.
The feels-like temperature, also called apparent temperature, is one number meant to capture how air actually registers on a human body. A thermometer measures only the air. The body responds to a mix of air temperature, sweat rate, evaporation, wind and direct sun.
Two formulas, two seasons
Above roughly 27°C, the calculation adds humidity through the heat index. Below roughly 10°C, it adds wind through the wind chill formula. The heat index is the US National Weather Service formula, built from temperature and relative humidity, and it is used for public warnings. Wind chill is the North American formula built from temperature and wind speed. A windy 5°C feels colder than a calm 5°C.
Mausam Online takes a different route. Its feels-like figure is the apparent temperature from Open-Meteo, a single formula combining air temperature, humidity, wind speed and solar radiation. The glossary notes that standard heat-index formulas assume shade, while direct sun can add up to 8°C to perceived heat.
Why humid heat is worse
Sweat cools the body only when it evaporates. At 85% humidity it does not evaporate efficiently, so cooling becomes very inefficient even at a “moderate” 35°C. Body temperature climbs while the thermometer stays put, and the risk of heat stroke rises.
That is why Mumbai feels hotter than Delhi at the same reading. Mumbai in May averages 70% relative humidity; Delhi averages 33%.
South Asia’s gap
During the summer monsoon, the glossary says, feels-like temperatures in South Asia often run 6 to 10°C above the air temperature. It lists some examples.
On the coast between May and September, Mumbai at 32°C actual feels like 42°C, a 10°C gap. Karachi at 35°C feels like 45°C at the peak of summer. Inland and dry, the picture changes. Delhi at its May peak reaches 44°C actual and 46°C feels-like. Sukkur in Pakistan goes from 47°C to 49°C. Relative humidity in those inland cities is often below 30%, so the heat-index formula adds little. In coastal cities, humidity of 70 to 85% disrupts evaporative cooling.
For coastal cities at the height of summer and monsoon, feels-like values routinely pass 45°C for hours at a time, which puts the whole population in the “Danger” zone. Outdoor workers, the elderly, children and people without air conditioning face the highest risk.
Not the same as wet-bulb
Wet-bulb temperature is a physical measurement: the lowest temperature reachable through evaporative cooling. Climate scientists use it. A wet-bulb reading of 35°C is considered the human survivability limit, and the glossary says even healthy adults face heat-stroke risk within hours at that level. Feels-like, by contrast, is a regression formula calibrated to perceived heat. Roughly, a feels-like of 54°C corresponds to a wet-bulb near 32°C, about the upper limit for safe outdoor exertion.
