The Inflow to Tropical Cyclone Humberto (2001) as Viewed with Azimuth–Height Surfaces over Three Days

Abstract The deployment of 228 global positioning system dropwindsondes (GPS sondes), over three consecutive days in Tropical Cyclone Humberto (2001), allows for the creation of azimuth–height (ϕ–z) surfaces from sea level to 3-km altitude at 0.25° and 0.5° latitude distance from the storm center. The authors estimate the radial flow along these ϕ–z surfaces to diagnose the mass flux through said surfaces as Humberto deepens from 1000 to 983 hPa from the first to the second day, then fills to 992 hPa by the third day. As the tropical cyclone (TC) intensifies the width, depth, and rate of inflow increase. The inflow remains a wavenumber-1 pattern throughout the three days. The center of the inflow rotates clockwise over this period following the expected forcing due to both the tropical cyclone motion and deep layer shear vectors. Net vertical mass flux, based on continuity within a given volume, is correlated with TC intensity only for the inner 0.25° ϕ–z surface. Slightly farther from the center, at 0.5° radial distance, the net mass flux is much larger but is not correlated with intensity. The rainbands that exist between the 0.25° and the 0.50° rings are ineffective at either creating or maintaining a warm core and lowering the surface pressure. The authors speculate that the warming associated with convective bands at larger radii is more easily eroded by the strong wind shear; convective bands nearer the center produce a more complete wind field that protects the warm core.