Tropical Storm Chris
Tropical Cyclogenesis Experiment
(940820I Aircraft 43RF)
| Scientific crew |
| Chief Scientist | H. Willoughby |
| Doppler Scientist | C. Samsury |
| Cloud Physics Scientist | S. Aberson |
| Dropwindsonde Scientist | J. Franklin |
| Workstation | J. Griffin |
| Observers | B. Burpee
D. Barram (Undersecretary of Commerce) |
This document is divided into 3 sections (Each section is written by the Chief Scientist):
Mission Briefing
In the morning of 20AUG94 tropical storm Chris was NE of Puerto Rico tracking NW. Over the preceding 24 h the forecasts had indicated an increasing northward component of motion so that we expected Chris to recurve, accelerate, and pass just to the east o
f a cold-core low centered near 30N 75-70W. The objective of the mission was to study the interaction between Chris and the low. We briefed for a takeoff at noon local time (1600 UT), and planned for a second sortie with takeoff at 2100 local (0100 UT). T
he intended flight tracks were the ``trefoil'' pattern of three 250 nmi equilateral triangles equally spaced about Chris' center. The aircraft were to maintain 500 mb PA throughout the flight.
Mission Synopsis
Departure from San Juan was delayed until 1724 UT to accommodate a VIP passenger. The approach to Chris was from the SW with an expected ETA of 1920 at the center near 25N 59W along a track that we expected to recurve to east of due north. At the IP 21N 6
2.5W, the aircraft encountered 20 kt wind from the SW, which continued until we reached 24N 59W at 1921. A mass of convection NW of track and banding in the low clouds indicated that we were SE of the center, and we turned toward the NW. The last fix from
the USAF reconnaissance confirmed that the center was in that direction. At 1948 we encountered a flight level wind center embedded in poorly organized convection near 25.5N 60.5W.
The outbound leg from the center continued the initial SW to NE leg to a point 240 nmi from the center. From there we turned W to a point 240 nmi NW of Chris' extrapolated center. During this part of the flight the meteorological situation seemed confused
, difficult to work with, and not at all like the target of the experimental design. These considerations led me to cancel the second sortie. The next leg of the pattern was from NW to SE. At 2224 near 26N 60W, a sudden strengthening of the wind and chang
e of direction from ESE to SW marked crossing shear line that Chris had become. The apparent center lay at the western end of an E-W band of convection. During the outbound leg toward the ESE we flew along to the line of convection, then turned northward
to a point 240 nmi E of the extrapolated center. The final E-W leg of the pattern traversed the line of convection in 45 kt southerly winds and apparently passed just south of a circulation center near 27N 59.8W at 0039 on 23AUG. Although the winds were w
esterly near the center, we encountered no northerly winds W of the center, and eventually the flight-level winds west of the center came from the south at less than 10 kt, consistent with the cold low's circulation. We continued the outbound leg along 27
N to 64.5W before turning southward to San Juan.
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 pas
s 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' i
ncorporation into the cold low.