By September 12, a central dense overcast developed and due to favorable conditions, the National Hurricane Center noted the possibility of rapid deepening.[6] Intensification continued at a quicker albeit less than rapid rate on September 12. Later that day, sustained winds reached 65 mph (105 km/h).[7][8] By early on September 13, convective banding wrapped almost completely around the center and cloud tops reached temperatures as low as −112 °F (−80 °C). However, because microwave satellite data could not determine if an eye had developed, Nadine's intensity was held at 70 mph (110 km/h) – just below the threshold of hurricane status.[9] The National Hurricane Center noted that "the window for Nadine to strengthen may be closing", citing computer model consensus of an increase in wind shear and little change in structure.[10] The storm then began experiencing moderate southwesterly wind shear on September 13, generated by a mid- to upper-level trough and a shear axis located a few hundred miles to the west of Nadine.