Tropical Storm Debby
Tropical Cyclogenesis Experiment
(940910I Aircraft 43RF)

Scientific crew
Chief Scientist F. Marks
Doppler Scientist H. Willoughby
Cloud Physics Scientist R. Black
Dropwindsonde Scientist J. Franklin
Workstation J. Griffin
Observers Fremmel (Radian Corp.)
One IMAX individual
One Mexican AF Meteorologist

This document is divided into 3 sections (Each section is written by the Chief Scientist):

Mission Briefing

N43RF was the synoptic mapping aircraft for the Tropical Cyclogenesis Experiment (TCGX). The nominal mission involved flying a figure-4 centered on Tropical Storm Debby with 300 nmi radial legs oriented along cardinal compass directions at 500 hPa. We int ended to deploy 8 dropsondes-at the midpoints and ends of the radial legs. Satellite imagery showed an exposed low-level center west of a mass of deep convection. We had an accurate forecast of the center's position and expected to be able to see the cent er if our flight track passed within 50-100 nmi of it.

Mission Synopsis

N43RF departed Opa-Locka at 1819 UT on 10SEP94. We had an 800 nmi ferry to an initial point (IP) at 19.5N 68W. We reached the IP at 2109 and tracked south-southeast through the Mona Passage between Puerto Rico and Hispaniola toward the forecast center. Co nditions at flight level were clear with widely scattered cumulonimbus and a broken stratocumulus undercast within 1-2 km of the surface. The wind was from the east-northeast at 7-10 m/s. By 2045 UT a mass of convection with abundant lightning appeared ah ead and to the left of track. We altered course to pass near the convection. At 2204 we flew over a swirl in the stratocumulus that marked the low level center at 15.5N 66W. We continued south-southwest to 12N 67E in the same flight conditions with wind f rom the north at 5 m/s. From this southernmost point we flew northwestward along the diagonal of the figure four to 15.5N 72W, nominally due west of the center, and turned eastward. By this time it was dark. The flight-level wind had been from the northea st along the diagonal leg, as expected, but the winds veered to from the south-southeast along much of the approach to the center from the west. Near the center, the wind finally backed from the north. Although the moonlight was too dim the reveal the low -level center, frequent lightning flashes from the nearby convection enabled us to locate it at 0057 UT on 11SEP94 near 15.6N 66.9W. In the convection on the east side of the center, the wind first blew from the north, then shifted from the south. As we c ontinued eastward, the flight-level wind veered, eventually blowing from the south at 10 m/s by 0224 UT when we reached the end of the leg at 15.5N 60W. Despite the complicated shifting of the flight-level wind, dropsonde winds showed a broad cyclonic cir culation at 700 hPa and below. N43RF recovered in Barbados at 0307 UT on 11SEP94.

Mission Evaluation and Problems

Poor communications and the bad initial guess for Chris' center position made the situation early in the flight seem more difficult than it was. In retrospect, we should have launched the second sortie. It was clear by the time we began the final E-W pass that Chris had been elongated along a N-S axis into a shear zone, possibly with multiple convectively induced centers arrayed along it. The E-W leg was in exactly the right place and, in combination with the low-level USAF data, should document Chris' in corporation into the cold low.