Strange ABS issue
 

Ok recently the ABS light has been illuminating and after checking the front pads they were low so they were replaced along with the rotors. Rears have about 50% left. Cleaned the sensors.
Now here is the weird thing, in dry hot warm days the ABS light will always come on as soon as the car starts rolling. although on days of rain the ABS light never comes on and ABS works fine.

What could this be? Its very odd and happens everytime rain and dry.

You didn't mention the model of vehicle, but try wiggling the sensor wires prior to rolling the car. The other likely possibility is the brake light switch. As soon as you release the brakes and the car starts rolling, the ABS light will come on if the switch is faulty. This can also be temperature dependent. It is on my C280.

Ekk, its a 1990 420 SEL.