Your MBA isn't overheating, or it would shut down. It's quite normal for parts of the body to become hot to the touch under heavy workloads.
If you're not already doing so, use
iStat Pro (free) or
iStat Menus ($16) to get accurate readings of your temps, fan speeds, etc., rather than relying on your sense of touch or sound. A forum member has posted a copy of iStat Pro that has been "tweaked" to enhance compatibility with recent OS X versions. You can download it
here.