This paper addresses a variation of the ITU-R P.838-3 rain attenuation estimation method to obtain an estimation of the rain rate based on the actual observed attenuation of a microwave radio link. The radio link is 18 kilometers long and uses the 5 GHz U-NII unlicensed band for this purpose. The experiment takes place in the tropical city of Guayaquil, Ecuador. The results are later evaluated by comparing them with the actual average rain rate given by four rain gauges installed along the propagation path. In addition, this research adapts the Synthetic Storm Technique for the use of multiple rain gauges in a region with a considerable level of rainfall spatial diversity to obtain preliminary calculations of radio link attenuation due to rain.