During arrival, there was a thunderstorm and lightning over the airport, so the aircrew held for about 7 to 10 minutes. After a Beech Baron had landed, they began an ILS approach. An 8 to 10 degree crab was needed to compensate for the wind on final approach. The first officer was flying the aircraft. He reported that wind shear was encountered at about 50 to 100 feet AGL, but only slight rudder was required to straighten the aircraft. After a normal touchdown, speed brakes and reverse thrust were used. The aircraft veered left and the reverse thrust was cancelled. The first officer reported that rudder and brakes were applied, but braking was nil. He tried reverse thrust again. Subsequently, the aircraft went off the right side of the runway. While scrubbing marks were found from about 1300 to 3500 feet down the runway. The runway was not grooved. Also, the runway had less than the 1 percent gradient that was recommended by FAA Circular, AC No: 150/5325-2C.