Engine inlet temperature is measured by the T1 Probe. The T1 probe is heated to prevent icing. When in icing conditions or rain, the cooling effect (or latent heat transfer or whatever the scientists want to call it) on the probe causes an error in the measurement of temperature, possibly due to the cooling effect overpowering the anti-ice heating capability. This will cause the Max N1 limit or Max EPR limit to change.
I demonstrated this effect to a Rolls Royce engine representative in flight on an A330 with Trent engines through the tops of tropical cloud about 10 years ago. His eyebrows bounced off the overhead panel! RR eventually said that the EEC computed max thrust change caused by the incorrect temperature reading was safe. So don't expect anything from Mr Rosemount's deficient probes to change soon!