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Tropical Storm Marco Discussion Number 19
NWS National Hurricane Center Miami FL AL142020
400 PM CDT Mon Aug 24 2020
There has been little change to the structure of Marco over the past
few hours, with the deep convection and associated heavy rainfall
being sheared well to the northeast of the exposed center of
circulation. Based on earlier Hurricane Hunter aircraft and
scatterometer data, there was a small area of tropical-storm-force
winds in the strongest convection located about 50-75 n
mi offshore of the northern Gulf coast. Since the shower and
thunderstorm activity is persisting, it is assumed that these winds
are still occurring in that offshore area and the initial intensity
is being held at 35 kt.
The exposed vortex should continue to spin down as the center of the
cyclone reaches the southeastern Louisiana coast late this evening,
which would result in the coastal areas being spared from
experiencing sustained tropical-storm-force winds. The
official NHC forecast shows Marco weakening to a tropical
depression tonight, which is in agreement with the model guidance.
Strong vertical wind shear should strip away any remaining
convection associated with Marco at some point tonight, as indicated
by GFS and ECMWF simulated satellite imagery. When the convection
does diminish, most of the model guidance does not show any
significant new convection developing thereafter. So it is
anticipated that Marco will degenerate to a remnant low by Tuesday.
Marco's initial motion is northwest at 6 kt. As the cyclone
continues to weaken and degenerate to a remnant low, a turn to the
west-northwest is expected as the system becomes steered in the
low-level flow. The latest NHC track forecast is little changed from
the previous one, and is near the TVCN consensus track guidance.
1. Gusty winds, heavy rainfall, and lingering coastal flooding are
expected from Marco along portions of the Gulf Coast through this
evening. For information on these hazards see products from your
local National Weather Service office.
2. Tropical Storm Laura could bring dangerous storm surge, rainfall,
and wind impacts to portions of the U.S. Gulf Coast by the middle of
the week, and tropical cyclone wind and surge watches have been
issued for portions of the U.S. Gulf Coast.
FORECAST POSITIONS AND MAX WINDS
INIT 24/2100Z 29.0N 88.9W 35 KT 40 MPH
12H 25/0600Z 29.7N 89.9W 30 KT 35 MPH...INLAND
24H 25/1800Z 30.3N 91.8W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 26/0600Z 30.8N 94.0W 20 KT 25 MPH...POST-TROP/REMNT LOW