Leveraging Subjective Dvorak Technique Cloud Patterns to Understand Tropical Cyclone Evolution

The subjective Dvorak technique is a multistep process for providing routine estimates of tropical cyclone intensity. After making a cloud system center fix, satellite analysts at tropical cyclone warning centers and the NESDIS Satellite Analysis Branch classify a system with a subjective Dvorak technique cloud pattern. These cloud patterns capture the overall convective organization and environmental interaction of the storm. Using visible or infrared geostationary satellite imagery, satellite analysts determine whether the cloud system exhibits a curved band, shear, eye, embedded center, or central cold cover. After this stage, satellite analysts follow the cloud pattern procedure to converge on a Tropical Number (i.e., “T-number”), which is the primary information used to determine the current intensity.

Until recently, the Dvorak technique cloud pattern used in making a current intensity fix was not recorded in the archived Automated Tropical Cyclone Forecast system’s fix data nor consistently commented on in text bulletins, and thus was not available for the tropical cyclone community to use to understand global tropical cyclones. Starting in the 2010s, satellite analysts started routinely recording the cloud pattern used while making the fixes. And, recent work shows that this byproduct of the fix process provides clues into modes of intensity forecast failure. This work, by following a similar strategy, provides an image-based climatology of global subjective Dvorak technique cloud patterns. Exploration of this climatology provides keen insights about the observed cloud patterns and their relationships to tropical cyclone centric brightness temperature variability and lightning activity. To complement the meteorological exploration, machine learning provides techniques to automate the detection of Dvorak cloud patterns. Automated techniques would then allow for more robust convective organization monitoring as some patterns like central cold cover only last for a few hours, which the typical operational fix the cadence misses.

Disclaimer: The scientific results and conclusions, as well as any views or opinions expressed herein, are those of the author(s) and do not necessarily reflect those of NOAA or the Department of Commerce.