At the time, Hugo had been deepening rapidly for 12 h. The maximum flight-level tangential wind was 89 m s-1 at a radius of 12.5 km, however, the primary vortex peak tangential wind, derived from a 100-s filter of the flight-level data was estimated to be 70 m s-1, also at 12.5 km radius. The primary vortex tangential wind was in approximate gradient wind balance and characterized by a peak in angular velocity just inside the radius of maximum wind and had an annular vorticity structure slightly interior to the angular velocity maximum.
The EVM along the aircraft's track was roughly 1 km in diameter with a peak cyclonic vorticity of 1.25 10-1 s-1. The larger circulation center, with a diameter >15 km, was observed within the eye and exhibited an average orbital period of 19 minutes. This period is about the same as that of the angular velocity maximum of the axisymmetric mean vortex, and in reasonable agreement with recent theoretical and model predictions of a persistent trochoidal wobble of circulation centers in mature hurricane-like vortices. This study is the first with in-situ documentation of these vortical entities, which were recently hypothesized to be elements of a lower tropospheric eye/eyewall mixing mechanism that supports strong storms.