Landfalling tropical cyclones in the Eastern Pacific. Part I: Case studies from 2006 and 2007

This study focuses on the structure and motion of tropical cyclones that developed during recent seasons and made landfall in northwestern Mexico: John, Lane and Paul (2006) and Henriette (2007). These events were associated with active episodes of convective outbreaks and heavy rainfall throughout the mountain ranges of the Baja California Peninsula and the Sierra Madre Occidental.

The interaction of the cyclonic circulation with the regional topography, that resulted in intense convection, is documented using satellite imagery (GOES and TRMM) and rain-gauge observations. The structure of incident cyclones is further documented, as QuickSCAT-derived winds were analyzed to estimate low-level convergence and vorticity while the patterns of geopotential heights, moisture advection and wind shear were derived from NCEP's gridded analyses. Additionally, surface temperature and sea surface height anomalies from Topex/Poseidon/Jason provided the oceanic conditions that prevailed during the developing period of the cyclones.

The selected case studies are set in the climatological perspective, using the best-track dataset and rain-gauge network records, from the period 1971-2005. Our historical analysis is limited to systems that made landfall over the peninsula or the mainland of northwestern Mexico. During this period, nearly 600 tropical cyclones developed in the eastern Pacific and about 10% of them moved into the area of interest. Some of the recent (2006 and 2007) storms, when compared with previous events, resulted in a substantial contribution to the total accumulations received by network stations in periods of 24-72 hours.