That day, the National Hurricane Center (NHC) noted the potential that the system could eventually develop into a tropical cyclone, with its five-day development potential estimated around 20%.[2] By a day later, the NHC estimated a 50% chance that the wave would develop into a tropical cyclone within five days,[3] and increased the development potential to 90% by August 18. By that time, a distinct low pressure area developed within the wave, with rainbands located near the center, which were signs of a maturing weather system.[4] On August 20, satellite imagery revealed that the system developed a defined low-level circulation center (LLCC), with convection firing up around it. As a result, the NHC began issuing advisories on Tropical Depression Thirteen, while the system was located about 1,035 miles (1,670 km) east-southeast of the northern Leeward Islands.[5]