Changes in the speed of the Galileo probe caused by zonal winds created a small but measurable Doppler effect in the probe relay carrier frequency. Analysis of the probe relay link frequency allows direct measurements of the speed of Jupiter’s zonal winds beneath the cloud tops, The deep winds were prograde and strong, reaching a sustained 190 to 200 meters per second at an altitude marked by a pressure of 24 bars. The depth and strength of the zonal winds severely constrain dynamic modeling of the deeper layers and begin to rule out many shallow weather theories.