Nadine threatened the Azores while moving northeastward and then northward between September 18 and September 19, though a blocking ridge prevented the storm from approaching further toward the islands. Its closest approach to the Azores was about 150 miles (240 km) south-southwest of Flores Island on September 19.[1] The storm then re-curved east-southeastward on September 20, after the ridge weakened and the mid- to upper-level trough deepened.[1] By late on September 21, much of the remaining deep convection was composed of only a ragged convective band with warming cloud tops.[22] Operationally, the National Hurricane Center re-classified Nadine as a subtropical storm at 2100 UTC on September 21, mainly because it had a larger than average and asymmetrical wind field, as well as the development of an upper-level low pressure area near the center.[23] However, post-season analysis concluded that Nadine degenerated into a non-tropical low pressure area three hours earlier.[1]