Eye on the Sky

It’s All Relative

Humidity, dew point and comfort (or discomfort).

By Paul Wilkerson

Millions of temperate-climate dwellers have had this thought in the warmer months of the year—“Gosh it feels so humid out. Yuck!” For people living in the Turks & Caicos, humidity doesn’t seem to bother them as much, as they are likely acclimatized to the conditions. Once you have experienced enough hot and sultry days, your body naturally will adjust. On the other hand, travelers to the Turks & Caicos Islands, especially from drier climates, may be in for quite the shock as soon as the cabin doors are opened on the air-conditioned aircraft on which they just arrived.

Humidity is a function of the air temperature and the dew point. “Relative humidity” is basically how close the air is to 100% saturation. When we have 100% saturation of the air, the temperature and dew point are the same.  Any time the dew point is less than the temperature, you will see relative humidity values be lower as well.

Confused yet? Let’s talk a bit more about this dew point temperature. The dew point relates to how much water vapor is actually in the air. Water vapor is the gaseous form of water. As the dew point rises, so does the amount of water vapor in the air. As dew points decrease, the amount of water vapor in the air also decreases.

To understand this from a comfort perspective, we can look at this function in different climates. In the Islands, wind flow is always from the water, which transports moisture over the Islands, contributing to higher dew point temperatures. Contrast the Caribbean climate against the climate of western New Mexico and other high desert areas.

This lizards has the right idea for keeping cool!

In Caribbean climates, it is routine to see dew point temperatures of 74º to 82ºF, while air temperatures hover around 88ºF. As mentioned earlier, travelers will note upon arrival to TCI that the air feels sultry, and to a degree, wet. Doing activities outside in a Caribbean climate has a marked effect on the body as well. As you begin to sweat, the ability of your body to cool itself is degraded. In order for you to perspire properly and maintain comfort, it is imperative that your body is able to get rid of heat via perspiration effectively. When the air is already highly saturated, your body struggles to evaporate and add your perspiration to the already moist environment.

Contrast that with western New Mexico where the air temperature may be 93ºF and the dew point might be closer to 30º or 35ºF. Here, the air is very dry with lower amounts of water vapor. Just stepping outside in temperatures in the low 90s is usually still surprisingly comfortable. Start hiking and biking, doing any outdoor activity in this environment, and again your body will start to perspire to cool itself down. But there is a big difference. Remember that the lower the dew point, the less water vapor there is in the air. As a result, the relatively dry air can efficiently evaporate sweat from your body.  As this occurs, it is cooling your body by absorbing the heat via the process of evaporation. Therefore, when comparing climates, there are drastic differences in what the perceived comfort level of the air will be based on geographic location.

Finally, what makes a big difference in human comfort or discomfort when it comes to high humidity and high dew points, is the wind. The Turks & Caicos Islands are blessed to lie in a great spot, wind-wise. In general, the wind machine is usually on in the Islands. While the humidity may be high, when the winds are up, this will help with the cooling effect on the body. Even in a high humidity environment, the wind will evaporate some of the moisture from your skin as long as the wind continues to blow. At times, the wind dies off, especially overnight and into the early morning. It is at these times that it can be quite uncomfortable, as any perspiration your body produces will not be effectively removed. That is why it can literally feel “sticky” in very humid environments.

While the air may seem uncomfortable to us, it is important to know that this high humidity environment also serves as an important environmental condition for the Islands’ ecology. In the evening when the winds die off and the air cools, dew sometimes forms on surrounding plants and other objects such as cars. This dew does offer nourishment to plants that it forms on. While the dew may be in very small amounts, when this happens consistently over days or even weeks it can bridge the gap until the next rain falls.

Comfort and discomfort with regards to humidity levels is relative to each individual. On your next visit if you find the air uncomfortable, I challenge you to take a look at the flora and fauna and try to remember that it very well may be thriving thanks to those high dew points and humidity levels.

Paul Wilkerson is an American meteorologist and tourist who frequents the Turks & Caicos Islands. Along with his wife and two daughters, the Wilkersons stay actively engaged with Islanders throughout the year with his Facebook page Turks and Caicos Islands Weather Info.

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