While significant progress has been achieved in tropical cyclone (TC) track forecasting during the past three decades, prediction of TC intensity change often remains problematic. In order to make improvements, a better understanding of the mechanisms involved with intensification needs to be obtained. This can be accomplished by diagnosing storm structure as depicted by in situ observations from several platforms on different scales and relating analyzed features to intensification processes. One of the foremost goals of the Hurricane Landfall 2001 initiative of the U.S. Weather Research Project (USWRP) is to fully document the three-dimensional structure and temporal evolution of a mature TC and its environment throughout the depth of the troposphere and within 1000 km of the center over the course of two successive days. Ideally, the candidate storm would be undergoing a significant period of strengthening or weakening.

During 23-25 September 2001, the Hurricane Research Division (HRD) of NOAA Atlantic Oceanographic and Meteorological Laboratories under its annual Hurricane Field Program and NASA under CAMEX-4 conducted joint, multiple aircraft research flights into the inner core, rainband, and environmental regions of Hurricane Humberto over the Western Atlantic. These missions were part of the Coordinated Observations of Vortex Evolution and Structure (COVES) experiment. Five aircraft participated in COVES, including two NOAA WP-3Ds, a NASA DC-8, a NASA ER-2, and a NOAA Gulfstream-IV. During the first day of the experiment, Humberto was steadily strengthening and reached its peak as a Category 2 storm on the Saffir-Simpson scale; during the second day, Humberto weakened to a minimal Category 1 hurricane. On each of day of COVES, over 120 GPS-dropwindsondes were released from the research planes, accurately measuring winds every 0.5 s as they descended from flight level to the surface. A set of objective multi-scale, filtered analyses of these GPS-sonde observations, along with flight level and remote-sensed data, can be produced to obtain comprehensive snapshots of Humberto's kinematic structure. In particular, the distribution of the dropsonde observations allows for an unprecedented determination of the three-dimensional wind field in the rainband region. Preliminary results of wind analyses will be presented in Part 1 and related to the observed intensity changes.