Hi Can You Advise Please. What May Be The Cause

Hi can you advise please. What may be the cause that hand tend to shake for a second or so when elbow is bent and arm is in a lifting motion as in lifting a cup to take a drink. It is fine any other time and once the arm gets past a certain point the shaking stops but always seems to happen and has just started lately thank you .. the shaking starts when arm is lifted about 6 to 8 inches and stops when raised another couple of inches if this makes sense