 Hurricane Debbie in 1969 provided the best opportunity to test the underpinnings of Project Stormfury . In many ways it was the perfect storm for seeding : it did not threaten any land ; it passed within range of seeding aircraft ; and was intense with a distinct eye . On August 18 and again on August 20 , thirteen planes flew out to the storm to monitor and seed it . On the first day , windspeeds fell by 31 % . On the second day , windspeeds fell by 18 % . Both changes were consistent with Stormfury 's working hypothesis . Indeed , the results were so encouraging that " a greatly expanded research program was planned . " Among other conclusions was the need for frequent seeding at close to hourly intervals . 
