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Tropical Storm Marco Discussion Number  12
NWS National Hurricane Center Miami FL       AL142020
400 AM CDT Sun Aug 23 2020
 
Thunderstorm bursts continue to fire near the center of Marco, then 
weaken an hour or two later due to persistent shear. Overall, the 
storm's appearance hasn't changed with nearly all of the deep 
convection very near or northeast of the center. Although the 
satellite presentation is somewhat lacking at the moment, the 
earlier Air Force Reserve Hurricane Hunter mission found believable 
SFMR values to 60 kt, so that value remains the initial wind speed. 
 
The intensity forecast remains tricky with Marco due to its small 
size and marginal environment.  There are some models that briefly 
relax the shear today, which will likely be enough of a change to 
allow Marco to reach hurricane strength.  Later on, while the 
cyclone is near the coast of Louisiana, the shear is forecast to 
increase, but it is unknown exactly how close to landfall this will 
occur.  Our best forecast at this time is that the strongest winds 
will be confined to the coast, and that Marco will then weaken 
faster than most hurricanes do over the swamps of Louisiana due to 
the shear.  No significant changes were made to the intensity 
forecast, which is very close to the model consensus.  The new 
forecast necessitates the issuance of hurricane warnings for 
portions of southeastern Louisiana.
 
Marco continues moving north-northwestward or 335/11 kt.  This
general track and speed is likely today, with a turn to the
northwest and decrease in forward speed expected as the storm
weakens late Monday.  While the track forecast is essentially
unchanged from the previous one, there is still a fair bit of
spread in the model guidance, likely tied to the intensity
forecast.  The stronger guidance is near or northeast of the new
model consensus, due to the upper-level flow, and the NHC forecast 
leans in that direction, close to the previous official prediction.


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 next 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  23/0900Z 23.7N  87.0W   60 KT  70 MPH
 12H  23/1800Z 25.3N  87.6W   65 KT  75 MPH
 24H  24/0600Z 27.3N  88.6W   65 KT  75 MPH
 36H  24/1800Z 29.0N  89.7W   65 KT  75 MPH
 48H  25/0600Z 29.9N  91.5W   45 KT  50 MPH...INLAND
 60H  25/1800Z 30.5N  93.1W   30 KT  35 MPH...INLAND
 72H  26/0600Z 31.0N  95.0W   25 KT  30 MPH...INLAND
 96H  27/0600Z...DISSIPATED
 
$$
Forecaster Blake
 
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