[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 240858
TCDAT4

Tropical Storm Marco Discussion Number  16
NWS National Hurricane Center Miami FL       AL142020
400 AM CDT Mon Aug 24 2020

Marco is clearly weakening tonight.  Data from an Air Force Reserve
Hurricane Hunter mission showed that flight-level and SFMR had
decreased along with a substantial rise in central pressure.  In
addition, GOES-16 1-min satellite data show the surface center well
displaced from the deep convection, and it appears that Marco is
decoupling from its mid-level circulation to the northeast.  The
initial wind speed is set to 50 kt, and that could be generous.

Some large changes have been required on this forecast. Considering
the shear is only forecast to increase, there is no significant
chance that Marco re-intensifies to a hurricane, and the hurricane
warnings have been replaced with tropical storm warnings.
Furthermore, now that the storm is losing vertical coherence, the
intensity forecast has been decreased as well, and is fairly
consistent with the model consensus and almost every model.

Marco has turned northwestward this morning at about 9 kt. The
storm should gradually turn westward as it approaches southeastern
Louisiana due to the shallower cyclone feeling the low-level ridge.
Marco will likely dissipate in a couple of days near the
Texas/Louisiana border due to continued strong shear.  Guidance has
come into better agreement on the track going slightly inland or
just brushing the Louisiana coast, and the track has been nudged
southward on this advisory.  It should be noted that the heaviest
rain and strongest winds will likely be northeast of the center, so
users should not focus on the exact track of the cyclone.


Key Messages:

1. Gusty winds, dangerous storm surge, and heavy rainfall are
expected from Marco along portions of the Gulf Coast beginning
later today. Interests in these areas should follow any advice given
by local government officials.

2. Tropical Storm Laura could bring additional storm surge,
rainfall, and wind impacts to portions of the U.S. Gulf Coast by the
middle of the week. This could result in a prolonged period of
hazardous weather for areas that may also be affected by Marco.
Interests there should monitor the progress of Marco and Laura and
updates to the forecast during the next few days.


FORECAST POSITIONS AND MAX WINDS

INIT  24/0900Z 27.6N  88.2W   50 KT  60 MPH
 12H  24/1800Z 28.6N  89.2W   45 KT  50 MPH
 24H  25/0600Z 29.2N  90.8W   35 KT  40 MPH...INLAND
 36H  25/1800Z 29.5N  92.7W   30 KT  35 MPH...OVER WATER
 48H  26/0600Z 29.4N  94.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  26/1800Z...DISSIPATED

$$
Forecaster Blake
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