No Rain Please!
In the rain even advanced drivers tend to revert back to the safe, but slow, practice of doing all of their braking in a straight line. Momentum is hampered in most of the slower turns when you drive this way. Keep the same approach and any attempts at increasing corner entry speed eventually result in under steer. Constantly needing to throttle steer through the corner leaves the driver with the impression that trying to go any faster at turn in is fruitless and only causes the car to push. In the rain traction is always the limiting factor, but additional grip can be given to the front tires if the braking is carried just past turn in. With the car pitched forward you can now combine a fair amount of turning with braking. The car is able to enter the corner at a better yaw and ultimately carry more speed. In fact for slower corners in the rain you may need to keep some load transferred forward for an even greater portion of the corner than you would in the dry. Since most drivers' tendency is to revert back to straight line braking carrying the brakes even deeper than you would in the dry is not an easy thing to do. As I bleed off the binders I sometimes use a heel/toe type technique in transferring my foot from the brake back to the throttle. I am not talking about shifting but rather momentarily using some gas and brake simultaneously as I roll my foot solely onto the gas pedal. If the brakes are carried deeper, the transition from brake to gas needs to be smoother.
Most if not all of the slow corners require at least one downshift and that offers an additional option. If you are very experienced with trail braking, and can heel/toe downshift very smoothly, you might also try to delay the last downshift until just before corner entry. However, this time blip the throttle just a bit less than you normally would so that the RPMs are just shy of a perfect match for the given gear change. As the clutch is released the rear of the car is then "braked" slightly by the engine. Like a brake bias adjuster might this in effect proportions more braking to the rear tires, but just at the given corner. When done well this type of "brake" allows the front tires to do more of the turning work while the rear tires slow the car and keeps the weight transferred to the front tires for additional steering grip. Rotation takes place allowing a straighter line and stronger acceleration to track out, an ideal situation in the rain. Smooth inputs are essential and are quite difficult since the cockpit is quite busy. A lot is going on in a very compressed period of time. Most often we like to do all of our downshifts in a straight line and with good reason. It is much easier to initiate a spin when braking and/or downshifting in a corner, be careful!
In wet fast corners exceeding the front tire's grip is not as much of an issue. Entering the corner under braking is usually not advised since transferring load is really not needed to get the car to turn. In fact, you may find that slightly increasing the length of your braking zone on wet fast sweepers allows you to time a smooth release of the brakes right before the turn in, and at the exact speed you need.