Secondary eyewall dynamics as captured by an unprecedented array of GPS dropsondes deployed into Edouard 2014

We discuss secondary eyewall formation and eyewall replacement cycle dynamics as captured by an unprecedented array of GPS dropsondes deployed into Edouard (2014). Hurricane Edouard (2014) evolved from a storm with a single eyewall on 9/15 to one with a secondary eyewall on 9/17. After reaching its peak intensity on 9/16, the storm weakened quickly at a rate of 20 m s^-1 per day as an eyewall replacement cycle took place.

We present an analysis based on a total of 136 GPS dropsondes with two periods of study. We denote the first period of study as the “secondary eyewall formation” period. This period was sampled with 49 GPS dropsondes deployed from 3 NOAA aircraft (2 P-3 Orions and the G-IV jet) in a span of ~5 hours, from 14:13 UTC to 19:20 UTC on 9/15. The domain of this period spans 310 km radius from the storm center and extends from 10 m to 3 km altitude. In this period we focus on the boundary layer and diagnose the secondary eyewall spinup and related dynamics. The second period of study is denoted as the “decaying double-eyewall” period. In this period we analyze the 87 GPS dropsondes deployed from about 55,000 ft, by the Global Hawk aircraft. The domain of study for this period spans 640 km radius and extends from 10 m to 18 km altitude. The decaying double-eyewall period lasts ~18 hours, from 13:57 UTC on 9/16 to 16:53 UTC on 9/17. We show the evolution of the decaying storm during the observation period and diagnose ongoing physical processes. We discuss implications of our analysis into the current knowledge of tropical cyclone dynamics in general and of secondary eyewall formation and eyewall replacement cycles in particular.