Marco is sheared apart in the northern Gulf of Mexico

August 24th, 2020 |

GOES-16 Low-level Water Vapor Infrared imagery (7.34 µm), half-hourly from 0116 thorugh 1316 UTC, 24 August 2020, overlain with GOES-16 derived motion wind vectors at 250-350 mb (red) and Surface-900 mb (blue) (Click to animate)

Tropical system Marco (formerly a category 1 Hurricane) was weakened by shear overnight and early morning on 24 August (as forecast).  The half-hourly animation above, of GOES-16 Band 10, i.e., infrared “low-level” water vapor (7.3 µm), overlain with derived motion winds at upper (red) and lower (blue) levels (Click here to see only the water vapor animation;  here is the shear analysis from the SSEC Tropical website; Note in the animation how the number of low-level vectors increases greatly at the end of the animation as visible imagery becomes available at sunrise.  Also:  the shear in the eastern part of the domain, over the Florida Straits, suggests a favorable environment for Tropical Cyclone Laura, approaching western Cuba from the east) shows the effect of shearing.

Low level easterlies and upper-level southwesterlies mean that the vertical structure of the storm was interrupted:  the low-level circulation decoupled from the upper-level.   That is, the low-level circulation moved to the west as the mid- and upper-level parts of the storm moved north and east.  Result:  By sunrise, visible imagery (0.64 µm) showed the low-level swirl of the elongating near-surface circulation southeast of the mouth of the Mississippi River, and south and west of the main convection over and offshore of the northwest Florida panhandle.

GOES-16 Visible Imagery (0.64 µm) from Mesoscale Sector 2, 1129-1328 UTC 24 August 2020 (Click to enlarge)

For more information on Tropical Storm Marco, refer to the pages of the National Hurricane Center.

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