Driving in the rain or through a puddle, you may notice the brakes feel slightly off for the first stop - a bit weak, then normal again. This is normal wet-brake behavior. Here is why brakes feel different in the rain.
Water on the rotor
When the rotors are wet, a thin film of water sits between the pad and the rotor surface on the first application. That film reduces friction briefly, so the very first stop in the wet can feel slightly weaker until the pads wipe the rotor dry - usually within one light brake application.
The self-drying effect
The moment the pads touch the spinning rotor, they squeegee the water off and grip returns to normal. This is why a light tap on the brakes after driving through a puddle is a good habit - it dries the rotors so the next real stop is full strength; see how disc brakes work.
Rust bloom after wet nights
After rain or a humid night, rotors can form a light flash of surface rust that makes the first few stops feel grabby or noisy until it wears off - this is normal and clears within a mile; it is not the same as a warped rotor or brake fade; see what is brake fade.
When wet braking is a real problem
Persistent weak braking in the wet, pulling, or long-lasting noise points to worn pads, glazed rotors, or a sticking caliper - not normal wet behavior; see when to replace pads. Keep good grip with quality pads and hardware.