Characteristics of mesoscale convection over northwestern Mexico, the Gulf of California, and Baja California Peninsula

Mesoscale convective systems (MCSs) are frequent, but understudied, components of the warm season climatology in northwestern Mexico. This study provides an update of previous research on convective development and examines MCS life cycle, structure, and motion from July through September. It focuses on a region south of the North American monsoon core and, from 2009 to 2018 satellite observations, on patterns of cloud tops higher than 10 km above sea level. The diurnal cycle of convection shows cells initiating in the early afternoon over the Sierra Madre Occidental mountains and becoming better organized over the next few hours. These features typically move westward, grow upscale to reach maximum vertical extent near local sunset, and weaken during the night. However, there is a distinct region of deep convection over and off the coast of Nayarit (20-23 degrees N), in the Pacific Ocean, that remains active through the night and into the early morning, producing heavy rainfall and frequent lightning. Occasionally, the inner structure of these MCSs can move across the Gulf of California and reach the southern Baja California Peninsula. One particular long-lived, fast-moving MCS from July 23 and 24, 2014 was selected for in-depth analysis, because it was associated with weather conditions that included unusual precipitation and extreme winds. The MCS caused damage from sustained winds of tropical-storm strength and an intense gust front in the Los Cabos area, in the southern tip of the peninsula. This extraordinary MCS developed in the most unstable and humid environment recorded during the 1976-2018 period, and was supported by a collocated upper-level, inverted trough and a lower-troposphere tropical wave. We also found that the 10 most unstable conditions have all occurred after 2011, possibly indicative of a trend toward more frequent and favourable environments to spawn MCSs over the Gulf of California entrance.