What Precipitation Properties are Most Critical for Tropical Cyclogenesis? Evidence from a Multi-satellite Investigation of Developing and Nondeveloping Disturbances

Motivated by Bob Houze’s decades-long dedication towards understanding the organization of mesoscale convective systems, and in one application its involvement in tropical cyclone (TC) intensification, this study will analyze the precipitation properties observed during the formation stage of TCs. While organized convection has been identified as a favorable condition for tropical cyclogenesis for decades, the relative importance of deep convection versus stratiform processes towards genesis continues to be debated among observational and modeling studies. This research complements other observational studies by analyzing precipitation organization during the TC genesis stage using a comprehensive collection of satellite observations from multiple passive microwave sensors, including the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI), as well as the TRMM Precipitation Radar (PR). The case sample consists of 11 years (2003-2013) of developing and nondeveloping disturbances in the Atlantic, East Pacific, and Central Pacific, as well as West Pacific and Indian Ocean basins (nondeveloping cases are only available between 2009 and 2013 for the latter two). Nondeveloping disturbances are identified as those disturbances that do not exceed an “invest” classification by the operational centers.

This presentation will offer a detailed analysis on the organization and structure of precipitation (e.g., aerial coverage, distance from the developing circulation center, convective v. stratiform, as well as the depth, or intensity, of convection) multiple days before genesis. This analysis offers an opportunity to determine whether the properties of precipitation at, and just prior to, genesis are unique compared to previous days of the pregenesis stage.  Analyses of individual precipitation features (PF) within the broader precipitating area will also be shown, with the goal of quantifying how the size distribution of PFs evolves as genesis nears, to describe to what extent larger-scale, organized MCSs contribute to the total precipitating area versus smaller-scale, individual convective cells (particularly those that are deep and intense), and compare how the PF size distributions differ between developing and nondeveloping disturbances.