It strengthened rapidly; by the time position fixes could be taken, Nancy was nearly a super typhoon, on September 8.

Moving gradually westward, Nancy explosively deepened and reached wind speeds equivalent to a Category 5 super typhoon (Saffir–Simpson Hurricane Scale) on September 9.

Shortly after reaching peak intensity, Nancy approached the Ryūkyū Islands and began turning.

Nancy made landfall as a strong typhoon on September 16 as it passed directly over Cape Muroto.

The typhoon rapidly traveled up the length of the island as it continued accelerating, eventually reaching a forward speed of 65 mph (105 km/h; 56 kn).

[2] On Okinawa, low-lying areas experienced heavy flooding, which did significant damage to agriculture and structures.

Although the exact number may never be known, the Stars and Stripes reported in late September 1961 that over 1,056 ships and fishing vessels were sunk or blown ashore, and that many more were damaged.

A reconnaissance aircraft flying into the typhoon near its peak intensity on September 12 determined Nancy's one-minute sustained winds to be 185 knots (213 mph; 343 km/h).

[10] In 2016, reanalysis of Hurricane Patricia noted that the storm had the same sustained winds as Nancy, the highest on record in the Western Hemisphere.