Sunday, July 24, 2005

During the overnight flight (N43RF) T.D. #7 was upgraded to Tropical Storm Gert. Gert was positioned in the southern Bay of Campeche, but in the 11 AM EDT advisory NHC indicated the possibility of two centers, one located just north of the coast and the other located further north and west, possibly the one sampled by the overnight flight and tied to the overnight convective development. The plan called for a final follow-on P-3 mission to occur during the afternoon of July 24. At the time of takeoff on 17 UTC Gert was about 100 nm southeast of Tampico, Mexico, and was moving west- northwest at about 9 kt. It was hoped that the P-3 would be able to reach Gert before it made landfall, so that it could sample the west side of the storm.

The flight track called for a butterfly pattern intended to provide maximum azimuthal resolution to this weak system (Fig. 29). By the time the storm was reached most of the concentrated deep convection from the previous night had decreased in areal coverage, leaving some convection on the north and east side of the storm. Flight-level (not shown) and dropsonde data from the mission (Fig. 30) showed a complex pattern. Multiple wind shifts and pockets of winds at flight level suggested the possibility of multiple centers. The drops appeared to have captured the primary vortex at the surface, but this vortex center seemed displaced from the centers at 700 and 850 mb (850 mb not shown). It appeared that the surface circulation center was further east than the 700 and 850 mb center. The drops were unable to capture the multiple centers, but that is not surprising considering their coarser resolution. The flight-level data showed two, possibly three centers: one at about 21 N 97.2 W, one at 21.7 97.5 W, and perhaps a third inland at about 21.4 N latitude. The pattern seemed to indicate a broad circulation pattern that is fairly well-defined with an inner-core characterized by these multiple centers. The pattern was only captured east of the broad vortex, but the pattern was able to capture all or some of the smaller-scale vortices within this broader circulation. It will be interesting to compare these data with the data from the previous nightÕs mission to try to establish continuity with the small-scale vortices.

Rob Rogers
HRD Field Program director