Signs of Rapid Intensification as Depicted in the Microwave Imagery

This paper examines patterns in the microwave imagery that can help distinguish the differences between tropical cyclones (TCs) intensifying at faster versus slower than normal rates. Findings of the second author from an earlier study for rapidly intensifying TCs found different characteristic intensification rates depending upon the initial intensity of the TC. In addition, characteristic patterns in the EOF in the NCEP reanalysis fields were found for rapidly intensifying TCs. This study examines these cases for distinctive patterns in the microwave imagery. Operational forecasters have many empirical methods to determine whether a particular storm will intensify rapidly; however, these methods are often more reliable to determine whether a TC will intensify at all rather than provide any guidance towards intensification rates. Besides from having favorable environmental conditions such as warm sea surface temperatures and minimal vertical shear, it seems apparent that the degree of initial convective organization in the developing TC is next most important feature. This paper looks at 85 and 37 GHz microwave imagery for patterns in convective banding which are similar to those shown in the Dvorak technique. In addition, pre-eyewall features are examined which do not exist in the Dvorak technique. Finally, a comparison is made for any distinctive features that can be observed in the microwave imagery between rapid versus slowly intensifying TCs.