Cyclogenesis off the African Coast: The Case of Cindy in August 1999

Abstract

Using radar data from Dakar (Sengal), National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalyses, outgoing longwave radiation provided by the National Oceanic and Atmospheric Administration (NOAA) Television Infrared Observation Satellite (TIROS) satellite series as well as data from the National Hurricane Center (NHC), a cyclogenesis process leading to the birth of a tropical cyclone from a Sahelian mesoscale convective system (MCS) off the African coast of Senegal is described. The cause of this evolution seems to be the coincidence of the MCS with an easterly wave over a warm sea, the presence of a wide area of precipitable water vapor, strong convergence in the low and midtropospheric layers, and an easterly vertical shear of the zonal wind. As a result, a dynamically well organized convective system built up and the system rapidly strengthened. Before moving away from the African coast of Senegal, this perturbation, which became the tropical cyclone "Cindy," caused the wreck of more than a hundred fishing pirogues and the deaths of many fishermen because of the suddenness and speed of the phenomenon.

Radar characteristics of continental, coastal, and maritime convection observed during AMMA/NAMMA

“…Mesoscale convective systems (MCSs) are primary contributors of rainfall totals in West Africa (Le Barbé and Lebel, 1997;D'Amato and Lebel, 1998;Laurent et al, 1998;Mathon et al, 2002;Redelsperger et al, 2002;Fink et al, 2006), despite their small contribution to convective system population numbers (Mohr et al, 1999). Highly organized continental MCSs often take the form of squall lines (SLs) (Hamilton et al, 1945;Eldridge, 1957;Bolton, 1984;Houze et al, 1989), while systems in the adjacent east Atlantic region are often more stratiform in nature Houze, 2003, 2006;Fuentes et al, 2008), with a transitional region for systems exiting the West African coast (Sall and Sauvageot, 2005;DeLonge et al, 2010).…”

Regional comparison of West African convective characteristics: a TRMM‐based climatology

“…This instability leads to the formation and maintenance of (often intense) MCSs (Aspliden et al, 1976;Payne and McGarry, 1977;Houze and Betts, 1981;Barnes and Sieckman, 1984;Rowell and Milford, 1993;Hodges and Thorncroft, 1997;Mohr and Thorncroft, 2006;Nicholls and Mohr, 2010). These westward-moving systems generally exhibit a linear (squall line) morphology over the continent (Hamilton et al, 1945;Eldridge, 1957;Bolton, 1984), a non-squall (amorphous) morphology over the eastern Atlantic Houze, 2003, 2006;Fuentes et al, 2008), and a transition stage upon exiting the coast (Sall and Sauvageot, 2005;DeLonge et al, 2010).…”

The propagation and diurnal cycles of deep convection in northern tropical Africa

“…Yang and Slingo, 2001), which do not resolve the impact of some mesoscale systems. The interactions of mesoscale convection and easterly waves also present a challenge because they are not fully understood, yet they are critical to precipitation variability and they contribute to tropical cyclogenesis (Berry and Thorncroft, 2005;Sall and Sauvageot, 2005). Specific goals are to: (1) document the propagation characteristics of deep convection and compare those properties with those of other continents; (2) compute the mean diurnal cycle for sub-seasonal and seasonal periods; (3) identify large-scale dynamical influences on propagating convection; and (4) investigate the phase relationship of the episodes of deep convection and AEWs.…”