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Tropical Storm MARCO

Tropical Storm Marco Discussion Number  13
NWS National Hurricane Center Miami FL       AL142020
1000 AM CDT Sun Aug 23 2020
Deep convection with cloud tops of -75 to -80 degrees C has 
persisted over the center of Marco for the past several hours. An 
Air Force Reserve Hurricane Hunter aircraft currently investigating 
the cyclone measured winds equivalent to 62 kt both with the SFMR 
and in a dropsonde in the northeastern eyewall. However, the 
aircraft reported peak 850-mb flight level winds of only 64 kt. 
Based on a blend of these data it appears that Marco is on the cusp 
of becoming a hurricane, but is not quite there yet. Therefore, the 
initial intensity remains 60 kt.
Based on the SHIPS guidance, Marco has about a 12-24 hour window to 
intensify in an environment characterized by moderate southwesterly 
shear, very warm waters, and plenty of atmospheric moisture. After 
that time, the vertical wind shear is expected to increase and this 
should begin to dominate the cyclone's environment. The latest NHC 
intensity forecast is unchanged from the previous one, forecasting 
Marco to become a hurricane later today, and maintaining hurricane 
intensity up until landfall in agreement with the latest LGEM 
intensity guidance. While it is possible that Marco will weaken just 
prior to landfall due to the increasing shear, there is little 
difference in the impacts between a 60 and 65 kt system. 
Marco is moving north-northwestward or 340/12 kt. Although the 
overall guidance has not changed much since the previous advisory, 
there remains considerable spread in this guidance by the time Marco 
reaches the northern Gulf coast. This spread could be attributed to 
the varying ways the models handle the system as it encounters the 
more hostile environment near the coast. Since the track consensus 
aids have changed little through 36 h, the official forecast is 
essentially the same as the previous one through that time. The 
model guidance has shifted a little northward beyond 36 h, so the 
official forecast was nudged to the north during that time as well. 
Key Messages:
1. Hurricane conditions, life-threatening storm surge, and heavy
rainfall are expected from Marco along portions of the Gulf Coast
beginning on Monday, and Hurricane and Storm Surge Warnings have
been issued. 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.

INIT  23/1500Z 24.7N  87.3W   60 KT  70 MPH
 12H  24/0000Z 26.4N  88.1W   65 KT  75 MPH
 24H  24/1200Z 28.2N  89.1W   65 KT  75 MPH
 36H  25/0000Z 29.5N  90.4W   55 KT  65 MPH...INLAND
 48H  25/1200Z 30.5N  92.1W   35 KT  40 MPH...INLAND
 60H  26/0000Z 31.2N  93.8W   30 KT  35 MPH...INLAND
 72H  26/1200Z 31.8N  95.4W   25 KT  30 MPH...INLAND
 96H  27/1200Z...DISSIPATED
Forecaster Latto