Here's why:

* Sound is a vibration that travels through matter. The molecules in the matter vibrate and pass the energy along.

* Higher temperatures mean faster molecule movement. At 30 degrees Celsius, the molecules in the air are moving faster and bumping into each other more frequently.

* More frequent collisions mean faster energy transfer. This faster energy transfer allows the sound vibrations to travel through the air at a higher speed.

In general, the speed of sound increases with temperature.