On March 21, 2018, about 0524 eastern daylight time, a Gulfstream Aerospace Corporation G-V, N90JE, encountered turbulence while descending on approach to Miami International Airport (MIA), Miami, Florida. The two airline transport pilots and flight attendant were not injured. There were five passengers onboard, one sustained serious injuries, two sustained minor injuries, and two were uninjured. Night, instrument meteorological conditions prevailed, an instrument flight rules flight plan was filed. The flight was operated by Clover Aviation under the provisions of Title 14 Code of Federal Regulations Part 91. The flight departed Rio de Janeiro-Galeao International Airport (SBGL), Rio de Janeiro, Brazil, at 1050 eastern standard time. According to the SIC (second-in-command), while descending from 27,000 ft to 12,000 ft approaching MIA, the PIC (pilot-in-command) turned on the seatbelt sign. While descending to 9,000 ft the PIC cycled the seatbelt sign again and they began to encounter "light chop." The PIC noted red cells on his weather radar, the SIC did not note any cells on his radar. He suggested to the PIC they maintain their present course because he could see Miami's coastline behind a small layer of clouds. The PIC requested a left deviation from air traffic control (ATC), and they turned 20° left and entered clouds as they continued the descent to 4,000 ft; the PIC cycled the seatbelt sign for the third time. During the descent they encountered moderate chop and heavy precipitation. About 7,000 ft they instantly dropped 500-1,000 ft. The turbulence was moderate for a moment and ended at 5,000 ft. When they leveled off at 4,000 ft the flight attendant notified them some of the passengers may be injured. The crew notified ATC they had experienced moderate turbulence but did not notify them of the injured passengers. The three injured passengers did not have their seatbelts fastened at the time of the turbulence encounter. The weather conditions reported at MIA included wind from 290° at 9 knots, visibility 10 statute miles, temperature 22° C, dew point 19° C, and an altimeter setting of 29.87 inches of mercury. There were no Convective SIGMETs active for the event location at the event time. No lightning was detection associated with this convection.