A comparison will be made between a tropical depression that developed into a Hurricane (Dolly 1996) and a tropical depression that failed to reach tropical storm intensity (Tropical Depression #5 1997) using a unique dataset collected by NOAA P-3 aircraft during a tropical cyclogenesis experiment conducted by NOAA/AOML/HRD. Data used in this study includes Doppler radar data, dropsondes, scatterometer, and flight level data collected by the P3 aircraft in addition to 1 degree latitude/longitude ECMWF model output. Since tropical cyclogenesis is dependent upon several different scales of motion this study will be multiscale in its approach. Data from the two P3 aircraft will be used in conjunction with radiosondes, dropwinsondes and global model fields to examine interactions between the different scales of motion and show how they influence the process of tropical cyclogenesis.
An examination of the data collected during the formation of Hurricane Dolly (1996) showed that the transformation of the pre- Dolly disturbance to a tropical depression occurred as it interacted with an upper-tropospheric trough-ridge couplet. Mesoscale analyses created with the P3 Doppler data show that the tropical depression was composed of several different closed circulations that existed contemporaneously. The interaction of the depression with the upper-tropospheric flow pattern likely created an environment favorable for the existence of persistent, deep moist convection and aided in the intensification of the tropical depression to Hurricane Dolly.
Tropical Depression #5 (1997; hereafter TD5) formed in a similar manner to Dolly. At the onset of development, the synoptic-scale flow favored the existence of persistent, deep moist convection associated with TD5. The system slowly developed over the next two days, but then entered an unfavorable environment. Mesoscale analyses created with the P3 Doppler data showed the existence of mesoscale cyclonic circulations within TD5. It is hypothesized, however, that those cyclonic circulations were unable to intensify due to the existence of an environment unfavorable for synoptic-scale ascent and persistent, deep moist convection within TD5.