Dan Satterfield is the Chief Meteorologist for WBOC TV in Salisbury Maryland.
People across India are anxiously awaiting for the summer monsoon to kick in. It will bring flooding rains, but it will also cool the temperatures down to near 91°F (33°C) instead of the 117°F (47°C) they saw in some spots earlier this week.
The recent extreme heat is only part of the story, though. The dew point — a measure of humidity — reached up to 81°F (27°C). That is a combination of heat and humidity that almost no part of the U.S. has ever seen. That is deadly heat, even in the shade. With that much moisture in the air, the temperatures do not drop at night. There is little relief unless you have air conditioning, and many in India would consider that an unaffordable luxury.
Our bodies cool themselves with evaporational cooling — when we sweat the moisture cools our skin as it evaporates. You can measure how much cooling you will get by placing a wet cotton wick on the bulb of a thermometer, swinging it for about 45 seconds, and looking at the temperature. This is the wet bulb temperature, and from it you can derive the dew point and the relative humidity. Think about this though, if the wet bulb gets much above 90°F (32°C) degrees, your body is going to get very little cooling and it will actually start to heat up. The wet bulb has been near or above 30°C (86°F) on parts of India, approaching the level of deadly heat.
Now, think about this: if India warms like the rest of the land masses over the next several decades, then it is very possible, we will start to see wet bulb temperatures over 90°F before the summer monsoon arrives. That is literally too hot for most humans.
The summer monsoon is already arriving in India with rain over the southern parts of the sub-continent. The map below from the India Weather Service shows the expected dates that the Monsoon will arrive across the rest of the country. It will be very welcome.
Here is the view from the Terra satellite on Tuesday afternoon. Note the thunderstorm activity over southern areas of India. There’s also smoke and haze over northeast India, which is pretty much a constant due to cooking fires and automobile pollution.
Note: You might say that Death Valley regularly sees temperatures of nearly 125°F (52°C), but the air there is very dry. If you’re in the shade, with water, you can survive that type of heat because your sweat will help cool you due to the low wet bulb temperature.
This originally appeared on The AGU Blogosphere.