Data from: Documenting the progressions of secondary eyewall formations

Intense tropical cyclones can form secondary eyewalls (SEs) that contract
towards the storm center and eventually replace the inner eyewall, a
process known as an eyewall replacement cycle (ERC). However, SE formation
does not guarantee an eventual ERC, and often, SEs follow differing
evolutionary pathways. This study documents SE evolution and progressions
observed in numerous tropical cyclones, and results in two new datasets
using passive microwave imagery: a global subjectively labeled dataset of
SEs and eyes and their uncertainties from 72 storms between 2016–19, and a
dataset of 87 SE progressions that highlights the broad convective
organization preceding and following a SE formation. The results show two
primary SE pathways exist, No Replacement, known as Path 1, and
Replacement, known as the Classic Path. Most interestingly, 53% of the
most certain SE formations result in an eyewall replacement. The Classic
Path is associated with stronger column average meridional wind, a faster
poleward component of storm motion, more intense storms, weaker vertical
wind shear, greater relative humidity, a larger storm wind field, and
stronger cold air advection. This study highlights a greater number of
potential SE pathways exist than previously thought. The results of this
study detail several observational features of SE evolution that raise
questions regarding the physical processes driving SE formations. Most
importantly, environmental conditions and storm metrics identified here
provide guidance for predictors in artificial intelligence applications
for future tropical cyclone SE detection algorithms.