One of the simplest hypotheses to explain the onset of precipitation in tropical clouds is the existence of very large (> 20 micron diameter) wettable or soluble salt nuclei that, when carried through cloud base, can almost immediately begin to collect cloud droplets. According to the extensive measurements of Woodcock in Hawaii, giant salt particles can often occur in significant concentrations. Woodcock's observations in the presence of modest surface winds of 5-10 ms-1 show concentrations at elevations of cloud base (0.7-0.9 km) in the range of 100-1000 m-3 for salt particles with masses > 1 ng (corresponding to NaCl particles with diameters > 10 µm). In this talk, we will present measurements of particle size distributions as a function of altitude, wind direction and wind speed obtained in the Cape Canaveral region of Florida. The data were obtained by the NCAR C130, Wyoming King Air and French Merlin during numerous passes over the ocean and Florida mainland with several particle spectrometers during the Small Cumulus Microphysics Study (SCMS). Radar RHI sequences of the evolution of reflectivity are used to illustrate precipitation development. We then describe tests of the ultra-giant nuclei hypotheses using the Ochs and Yao parcel model. The data from the observations are used as input for the model calculations. Concentrations of cloud droplets produced in the model are compared with those actually measured during the Small Cumulus Microphysics Study and the computed model radar reflectivities are compared with the radar observed onset of precipitation based on Rayleigh scattering