Large-Scale Flow Patterns Conducive to Central American Extreme Precipitation Events during Autumn

Abstract:

The monthly frequency of daily extreme precipitation events (EPEs) over Central America during autumn is concentrated near enhanced terrain where upslope flow is highly favored. Based on the observed local synoptic features throughout autumn, EPEs are hypothesized to be largely driven by the combined effects of tropical disturbances, large-scale flow patterns related to the Caribbean low-level jet, and monsoon southwesterlies in the eastern North Pacific. An example of this flow pattern occurred in October 2018 with the passages of multiple tropical disturbances over Central America that led to major flash flooding and landslides. Extreme precipitation induced by the precursor disturbances and subsequent development of Tropical Cyclones (TCs) Michael and Vicente largely accounted for the extreme rainfall, with some areas such as Antalya, El Salvador, exceeding 500 mm of cumulative rainfall over a 7-day period. This study focuses on identifying synoptic patterns and precursor disturbances that govern the development of extreme precipitation events over Central America and places TCs Michael and Vicente into perspective relative to the climatological flow patterns observed throughout the region.

Given the relatively large contributions that tropical disturbances can have on monthly rainfall distributions in Central America, it is hypothesized that large-scale patterns similar to those associated with TCs Michael and Vicente are favorable for producing EPEs throughout autumn. An examination of the large-scale flow features related to the formation and evolution of EPEs will be performed through the use of PERSSIAN-CDR and ERA-5 datasets. Additionally, a climatology of EPEs from 1983–2018 will be objectively categorized based on the patterns associated with the frequency of their occurrence and overall percentile distribution. A time-lagged composite analysis of thermodynamic and dynamic variables (e.g., CAPE, integrated vapor transport, relative vorticity, and wind shear) will then be performed on binned EPEs to document the evolution of the dominate fields that generally lead to EPEs identified in the constructed climatology. Diagnostic fields used to investigate the evolution of EPEs will also be applied to TCs Michael and Vicente for consistency and comparison purposes.