A system that recently came off the coast of Africa is showing signs of development as it moves through the Atlantic Ocean and toward the Caribbean. According to the National Hurricane Center's latest forecast, the tropical wave is accompanied by a well-defined low pressure system and was located about 400 miles southeast of the southern Cabo Verde Islands at 8:00 a.m. Tuesday. N.H.C. said associated shower and thunderstorm activity continues to show signs of organization, and environmental conditions are conducive for a tropical depression to form during the next couple of days while system moves generally westward at about 15 mph across the eastern tropical Atlantic Ocean. N.H.C. gave the system a 70 percent chance of development in the next 48 hours, with the chances growing to 90 percent through the next five days, according to the forecast.…