Dewpoint temperature is the point at which the relative humidity falls to zero, the point at which the air hits 100% relative humidity, has nothing to do with relative humidity, is the point at which:
a. Water vapor condenses into liquid water; Criteria: Condensation, Saturation.
b. Atmospheric pressure is at its maximum; Criteria: Barometric pressure, Weather patterns.
c. Cloud formation begins; Criteria: Nucleation, Cumulus clouds.
d. Air temperature reaches its minimum; Criteria: Frost formation, Temperature inversion.