Tropical Storm Marco Special Discussion Number  18
NWS National Hurricane Center Miami FL       AL142020
100 PM CDT Mon Aug 24 2020

Marco continues to weaken as the deep convection has been stripped 
away from the center since this morning. An Air Force Reserve
Hurricane Hunter aircraft currently investigating the system has 
reported peak 925 mb flight level winds of 38 kt. Although 
there have been a few recent higher SFMR measurements that are due 
to rain contamination, a recent ASCAT overpass revealed only 
a small area of 30-35 kt winds.  Based on these data the initial 
intensity is being lowered to 35 kt and a special advisory has been 
issued to update the short-term intensity forecast and discontinue 
warnings for the Gulf coast. 

The showers and thunderstorms generating the tropical storm force 
winds to the northeast of Marco's center are forecast by most 
models to gradually dissipate through this evening. Based on how 
quickly the vortex has been spinning down and the anticipated 
decrease of convection, it is reasonable to assume that sustained 
tropical storm force winds will no longer reach the northern Gulf 
coast. Therefore, all wind and surge warnings for the Gulf coast 
associated with Marco have been discontinued. Shortly after the 
cyclone reaches the Gulf Coast later tonight it should degenerate to 
a remnant low, with this low dissipating inland within a couple of 
days. The latest intensity forecast was adjusted downward through 12 
h, but remains the same as the previous NHC forecast thereafter. 

Marco has been moving slowly all day, and an initial motion 
estimate is now 320/5 kt. There is no change to the forecast track 
reasoning. As the cyclone continues to weaken and degenerates to a 
remnant low, a turn to the west-northwest is expected as the system 
becomes steered in the low level flow. The latest forecast track 
was adjusted slightly northward through 12 h, but remains the same 
as the previous one until the system dissipates.

This special advisory package replaces the 100 PM CDT (1800 UTC) 
intermediate public advisory.

Key Messages:

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 
and warnings could be issued for portions of the U.S. Gulf 
Coast later today. 

FORECAST POSITIONS AND MAX WINDS

INIT  24/1800Z 28.7N  88.6W   35 KT  40 MPH
12H  25/0000Z 29.4N  89.3W   30 KT  35 MPH...INLAND
24H  25/1200Z 30.0N  91.3W   30 KT  35 MPH...POST-TROP/REMNT LOW
36H  26/0000Z 30.5N  93.6W   30 KT  35 MPH...POST-TROP/REMNT LOW
48H  26/1200Z 30.9N  95.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
60H  27/0000Z...DISSIPATED

$$
Forecaster Latto