Because you add 87 degrees to your body temperature. It is all about perspective. Those who live in a hot climate find it cold when the outside temperature is 60 degrees.

The human body is--among other things--a heat engine. That means that a flow of heat from the hot place to a cold place is able to power other kinds of energy, just as 1000-degree burning gasoline vapor in an engine turns chemical energy into mechanical energy in the tires and electrical energy in the alternator. BUT that 1000 degrees has to flow to a cooler place to do so, just as water in a water wheel has to go froma higher place to a lower place. The 1000 degree gasoline vapor has to flow to the 87 degree atmosphere. Well, so does the 98.6 degree chemical energy in your body, and it so happens that we feel most comfortable when there is about a 30 degree difference between the inside of our body and the outside. We can tolerate 20 degrees more or less, but the more it is, the less we like it.

we know that under this condition our body temp is higher than outside temp. it means ( according to "prinsip air terjun") that we will get rid of the heat although we feel hot. so now the question is : why do we feel hot? i think ( i'm not so sure myself) it's because the rate of heat flow going out of our body is slower when the difference between temp outside and inside our body is smaller (that is, in this case, by increasing the outside temperature). that's what makes our body retains the heat longer than usual. hmm, what do u think? does it make sense? ps: sorry, my english sucks....

1) "Several reasons. One is that sunshine warms the skin directly. Another is that the brain tells you to feel warm or cold not just based on the temperature difference between your body and the air, but based on special cells in the skin that signal the brain what the temperature is. The responses of these cells is not just based on skin temperature and air temperature, but in part on a prediction of your body's need to start behaviors that will help it get rid of heat building up inside. So when it's 33C outside, it is difficult for you to get rid of heat fast enough, even though the body is warmer than the air, so your brain tells you to feel hot, and to sweat, etc, etc." Source and further information: http://www.newton.dep.anl.gov/askasci/bio99/bio99284.htm 2) "We asked Dr. Matthew Kluger of the Medical College of Georgia. He says our bodies constantly generate a lot of heat because of our metabolism. So we have to constantly lose heat to maintain our normal temperature. Kluger: So the bigger the gradient between our body and the environment, the more rapidly we can get rid of that heat. So when it's hot outside, our bodies sweat and increase blood flow to the skin to cool down faster." "This may not be a question that you've thought about, but it tells us something important about both basic physics and the way our body works. If you put a bucket of warm water outside, and that warm water just happened to be 98.6 degrees Fahrenheit, but the outdoor temperature was 85 degrees Fahrenheit, the water would cool down. That's because the outdoor temperature, while still warm, is cooler than the temperature of the water. Heat naturally flows from warmer places to cooler places. The heat's "goal" is to reach equilibrium–a state where everything is the same temperature as everything that surrounds it. That's why a hot bowl of soup or a cold glass of soda will eventually reach room temperature if you leave them out long enough. The difference between you and a bucket of water (well, one of many differences) is that your body is constantly generating more heat. All that heat has to go somewhere, so it tries to escape through your skin. The greater the difference between the outside temperature and the temperature of your body, the faster that heat will escape. That's why you'll feel much cooler on a 60-degree day than on a 90-degree day. The sun is another factor to consider. When meteorologists measure the temperature outside, they measure it in the shade. However, if it's 90 degrees in the shade and you're out in the sun, you're absorbing additional heat from the sun. That makes your body have to work even harder to lose enough heat to keep you comfortable. If you were a cold-blooded animal, like a lizard, the rules would be different. These animals don't generate nearly as much internal heat as mammals do. (Generating your own body heat to maintain a constant temperature is called thermoregulation.) So if a lizard goes into the shade on an 85-degree day, its body temperature would get very close to 85 degrees. So a lizard is more like a bucket of water than you are. Isn't that nice to know?" Source and further information: http://www.sciencenetlinks.com/sci_update.cfm?DocID=250