Re: Marco seems to be going toward FL Panhandle
Posted by
Chris in Tampa on 8/25/2020, 4:17 pm
I think Marco was being steered in part by the winds that were sheering it. The low level circulation was able to head toward the west, pretty devoid of convection, once it decoupled from the rest of it that was getting sheered.
By definition, a tropical cyclone has deep convection. At some point after it no longer had that, the NHC would say it was post-tropical.
Tropical Cyclone:
"A warm-core non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters, with organized deep convection and a closed surface wind circulation about a well-defined center. Once formed, a tropical cyclone is maintained by the extraction of heat energy from the ocean at high temperature and heat export at the low temperatures of the upper troposphere. In this they differ from extratropical cyclones, which derive their energy from horizontal temperature contrasts in the atmosphere (baroclinic effects)."
From: https://www.nhc.noaa.gov/aboutgloss.shtml#TROPCYC
Some other definitions from that page:
Post-tropical Cyclone:
A former tropical cyclone. This generic term describes a cyclone that no longer possesses sufficient tropical characteristics to be considered a tropical cyclone. Post-tropical cyclones can continue carrying heavy rains and high winds. Note that former tropical cyclones that have become fully extratropical...as well as remnant lows...are two classes of post-tropical cyclones.
Remnant Low:
A post-tropical cyclone that no longer possesses the convective organization required of a tropical cyclone...and has maximum sustained winds of less than 34 knots. The term is most commonly applied to the nearly deep-convection-free swirls of stratocumulus in the eastern North Pacific.
Extratropical:
A term used in advisories and tropical summaries to indicate that a cyclone has lost its "tropical" characteristics. The term implies both poleward displacement of the cyclone and the conversion of the cyclone's primary energy source from the release of latent heat of condensation to baroclinic (the temperature contrast between warm and cold air masses) processes. It is important to note that cyclones can become extratropical and still retain winds of hurricane or tropical storm force.
Extratropical Cyclone:
A cyclone of any intensity for which the primary energy source is baroclinic, that is, results from the temperature contrast between warm and cold air masses. |
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