Observations of inner-core moisture evolution during periods of pre-rapid intensification

Rapid intensification (RI) of tropical cyclones has become an active area of research due to its potential threat to coastal regions. Previous numerical simulations of unorganized, immature tropical low pressure systems have shown the necessity to pre-moisten the lower-to-mid levels of the troposphere via detrainment and precipitation from convective towers. A sufficiently moistened inner core produces conditions favorable for vortex intensification via asymmetric convection, vorticity anomaly production, axisymmetrization, and merger processes. These conditions have been demonstrated to aid cyclogenesis in numerical simulations, but have yet be documented prior to rapid intensification more mature tropical cyclones. The objective of this study is to examine the characteristics and evolution of low-level, inner core moisture observed in the pre-rapid intensification (pre-RI) environment (up to 24-h in advance of an RI event) in order to elucidate common moisture signatures unique to the ramp-up to RI.

This study utilizes an extensive flight-level dataset collected during repeated aircraft penetrations of the low- and mid-levels of Hurricane Wilma (2005) over a 10-day period, including several RI events. Estimates of the relative humidity and radial convergence are derived from ~50 unique figure-four penetrations/circumnavigations within ~250 km of the center of circulation. The azimuthal and radial distribution, magnitude, and evolution of moisture are evaluated with respect to the 200-850 hPa vertical shear vector for pre-RI, RI, and non-RI periods. A synopsis of our preliminary results and an expansion to other storms will be presented at the conference.