Observations by the NOAA WP-3D of a persistent mesoscale convectively generated vortex well displaced from the center of Tropical Storm Karen (2013)

On the afternoon of 4 October 2013, the NOAA Aircraft Operations Center WP-3D was conducting a Tail Doppler Radar data collection mission on behalf of the NCEP Environmental Modeling Center (EMC) and the AOML Hurricane Research Divison (HRD) into Tropical Storm Karen in the Gulf of Mexico.

During the third pass toward the center, inbound through the southeastern quadrant at a distance of approximately 75 nautical miles from the center, the crew observed an unusual mesoscale convective feature which contained a circulation that, for a surprisingly large spatial expanse, overwhelmed the larger sclae primary vortex. This feature also contained maxima of temperature and thera e along with minima for extrapolated surface pressure, geopotential height, and flight level winds. A dropwinsonde released into this feature recorded a wind profile that in no way resembled what would be expected 75 miles southeast of the center of a tropical cyclone.

This convective feature persisted (separately from the center of TS Karen) for the next 66 hours, well after the center of Karen moved ashore in Louisiana and NHC advisories on the storm were discontinued on the early morning of 6 October. Remnants of Karen became involved in a strong mid latitude trough and frontal system that swept eastward across the Gulf of Mexico. The mesoscale convective feature became embedded in this baroclinic zone and did not make landfall until the afternoon of 7 October in the Big Bend Region of the Northern Florida Gulf Coast.

Subsequent aircraft reconnaissance missions flown by both the NOAA WP-3D as well as the USAF Reserve 53rd WRS WC-130J continued to show flight level evidence of this feature until such flights ended late in the afternoon of 5 October. Land based radar as well as satellite imagery clearly show what aappears to the same discrete barotropic vortex associated with deep convection embedded within the larger scale high shear baroclinic environment of the eastern Gulf of Mexico from the afternoon of 6 October through landfall in Florida about 24 hours later.