 Robert Simpson became its first director , serving in this capacity until 1965 . There were several guidelines used in selecting which storms to seed . The hurricane had to have a less than 10 percent chance of approaching inhabited land within a day ; it had to be within range of the seeding aircraft ; and it had to be a fairly intense storm with a well @-@ formed eye . The primary effect of these criteria was to make possible seeding targets extremely rare . 
