Atmospheric conditions are known to affect the Received Signal Level (RSL) in commercial microwave links (MWLs), that operate at frequencies of tens of GHz. Study of these effects is of great importance both for communication engineers and for environmental monitoring. In this paper we study the phenomenon of a wet antenna. During periods of high relative humidity (RH), a thin layer of water may collect on the outside cover of the microwave units, resulting in increased signal attenuation. Here, we focus on the estimation of the signal power loss caused due to this phenomenon. We used a generalized likelihood ratio test (GLRT) to detect transient signal loss of unknown arrival time and duration, based on existing measurements from a network of commercial MWLs, used in for cellular backhauling. The results indicate the ability of the proposed algorithm to detect and estimate the signal loss of antenna moistening. Beyond its value for commercial microwave networks design, this information holds potential for the detection of dew, which is of great environmental importance.