Actually when the temperature rises, the human body feels hot and perspires. When the sweat is evaporated, it gives a feeling of cooling. During the pre-monsoon season which is very hot in North West India and the adjoining Pakistan, temperatures over 110 F are common. The human body survives this great heat because the season is exceptionally dry (with typical relative humidity in the afternoon as low as 10 percent). So the combined effect of very high temperature with very low humidity is that the apparent temperature or the heat index falls and according to the calculator developed by the National Weather Service, US, the index in this case is 104 F. It means that with an air temperature of 110 F and a relative humidity of 10 percent, the human body FEELS a temperature of 104 F. In other words it senses temperature 6 F lower than it actually is!
When the monsoon arrives in the Province of Pakistani and Indian Punjab, about the first week of July with its thick clouds and heavy rain, the temperatures fall sharply and within a matter of few days, when the monsoon is fully established, the typical midafternoon temperature of Lahore is 97 F with 60 percent relative humidity. Now when the same calculator, as mentioned above is consulted, it gives us the apparent temperature or heat index of 119 F! That is, the body feels as if the temperature outside is 119 F and not 97 F. It feels 23 degrees hotter it actually is. It feels highly uncomfortable. Consequently, heatstroke becomes very likely as human body is unable to cool itself.
The reason for this discomfort is that due to an increase in relative humidity of the air in the atmosphere, the air reaches near its saturation stage and is unable to take more moisture. So, as a result, rate of evaporations retards considerably. Now as human body cools itself by the process of evaporation of sweat from the body, it cannot cool itself properly and feels very hot and uncomfortable. If these high heat index conditions prevails for longer periods, severe threat to human health is highly likely.
So, in short, monsoon is a mixed blessing. On one hand, it brings cool wind and much awaited rain to North West India and adjoining Pakistan but on the other hand it increases the heat index to dangerous levels which is injurious to human health.