Control Winds states
You alter wind force in the area surrounding you. You can make the wind blow in a certain direction or manner, increase its strength, or decrease its strength. The new wind direction and strength persist until the spell ends or until you choose to alter your handiwork, which requires concentration. You may create an “eye” of calm air up to 80 feet in diameter at the center of the area if you so desire, and you may choose to limit the area to any cylindrical area less than your full limit....
Wind Strength: For every three caster levels, you can increase or decrease wind strength by one level. ...
My question is if a 10th level caster casts control winds, with the ambient wind being at moderate, can you instantly increase the wind speed by 3 steps (to windstorm) or do you need to "ramp up" the wind over the course of 3 turns/standard actions?
Follow up question. Assuming the ambient wind is moderate. Is the maximum force of wind that a 10th level casts could conjure would be Windstorm levels of wind even if they spent additional rounds concentrating trying to raise it higher?