The reason why the descending or sinking air in the eye of a hurricane is dry is due to the phenomenon of adiabatic warming.
In a hurricane, the eye is an area of calm and relatively clear skies, surrounded by the intense winds and rain of the eyewall. The sinking air in the eye descends rapidly, and as it does so, it undergoes compression due to increasing atmospheric pressure. This compression leads to an increase in temperature, which is known as adiabatic warming.
When air warms up due to compression, its relative humidity decreases. Warmer air can hold more moisture, so even if the actual moisture content doesn't change, the relative humidity drops. This results in drier air in the eye of the hurricane. Consequently, this dry air contributes to the distinct clear and calm conditions found within the hurricane's eye.
