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This loop of GOES-8 6.7 micron IR (water vapor) imagery shows no evidence of the low-level mesoscale vortex over the western North Atlantic Ocean (centered near 31 N latitude, 73 West longitude) on 15 September 1998. The weighting function of this GOES IR channel peaks in the middle to upper troposphere (normally between about 500 and 300 hPa). Colder brightness temperatures (-32 to -62 C) are given a white to blue enhancement.
The first image (at 11:45 UTC) shows the 12:00 UTC ETA model 400 hPa wind streamline analysis. The ETA model showed that an upper-tropospheric cyclonic feature was located to the southeast of the low-level vortex; this cyclonic feature was revealed well by the water vapor imagery, and remained nearly stationary while the low-level vortex propagated westward. An upper-level anticyclone was situated to the northeast of the low-level vortex. This pattern resulted in an easterly flow aloft over the vortex region.