An extratropical cyclone developed on December 2 in the eastern Atlantic Ocean about 1430 miles (2300 km) southwest of the Azores islands. It moved northwestward, then turned to the north, and developed gale force winds on December 4 after turning to the northeast. Later that day, it turned into a frontal low pressure system. As high pressure existed across the northeast Atlantic Ocean, the storm turned to the southeast. The system turned to the south-southwest on December 7. Later that day, thunderstorms formed around the center, and it is said that the system organized into a subtropical storm late on December 7 while located 835 miles (1340 km) south-southwest of the Azores. The storm moved to the southwest over warmer waters, and the thunderstorms, or convection, around the storm continued to get stronger. The convection became near the center as rainbands developed around the center. Since the storm was gaining more strength, the National Hurricane Center declared the system Tropical Storm Peter on December 9 while located 980 miles (1580 km) northwest of Praia in the Cape Verde islands.