A general rule would be to calculate your Out of Ground Effect(OGE)+5% hover performance calculation or equivalent for your machine, and ensure you have that performance. Due to your movement across the ground you will not have In Ground Effect(IGE) performance i.e. ground effect benefits, when you are at zero airspeed therefore requiring OGE performance.
OGE +5% should allow you to hover in free air and overcome light turbulence without exceeding the power limits. Light turbulence is defined as updraughts and downdraughts not exceeding 2-300' per minute (met office). Therfore you should be able to climb vertically in still air in the hover and acheive a rate of climb of 300' per minute. Alternately you could increase your aircraft weight by 5% and maintain a hover but drift up and down with the turbulence.
If you haven't calculated OGE +5% then for SA342 a rule of thumb is 10% torque in hand before attempting the departure. Regards!