This study presents a simple methodology to estimate diurnal patterns in dew point temperature/relative humidity on weekly basis from mean minimum temperature or the morning relative humidity under semi-arid climatic conditions of Hyderabad. The sinusoidal and exponential models for day time and night time temperature pattern have been utilized in working out the diurnal patterns of the relative humidity on weekly basis at Hyderabad. Diurnal variation in dew point has been found to have, by and large, a set pattern depending upon the morning dew point temperature. Diurnal relative humidity patterns have been worked out both from the estimated dew point/relative humidity and the actual recorded relative humidity. This model is expected to be quite useful for long term retrospective agro-climatological studies wherein daily relative humidity and/or diurnal patterns thereof are required as input.