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Tropical Storm Franklin Discussion Number   4
NWS National Hurricane Center Miami FL       AL082023
1100 AM EDT Mon Aug 21 2023

There are no lack of cold cloud tops associated with Tropical Storm 
Franklin this morning. The structure on satellite consists of a 
large bursting pattern, with cloud tops as cold as -90C close to and 
just east of the estimated center. However, it is unclear if any of 
this deep convection has resulted in structural improvement to 
the storm, with the most recent microwave imagery from a SSMIS F-16 
pass at 1007 UTC showing a chaotic structure, with evidence the 
center remains near the western edge of this large convective 
shield. The latest subjective satellite intensity estimates form 
TAFB is unchanged from earlier this morning. Thus, the initial 
intensity will remain 45 kt this advisory, which is also close to 
the latest D-MINT and D-PRINT estimates from UW-CIMSS. 

Franklin does appear to be slowing down a tad this morning while 
moving westward, with the latest estimate at 270/5 kt. The track 
forecast in the short-term is a bit problematic, with a large spread 
in model solutions even at 12 h, much higher than the climatological 
spread. This initial uncertainty may be related intensity 
differences in the global models, with some of the stronger guidance 
suggesting the tropical cyclone might reform further to the north 
and east over the next 12-24 hours. Thereafter, a large weakness to 
the north of Franklin, produced by a large mid-ocean trough draped 
across the Western Atlantic, should allow the storm to begin moving 
northward. A mid-latitude trough reinforces this weakness to the 
north in 60-72h, allowing the storm to begin moving northeastward. 
The most significant change in the guidance this cycle is the 
majority are quite a bit slower than the prior cycle, and the NHC 
forecast track was slowed down a bit, but not as much as some of the 
consensus aids.

Currently, Franklin is experiencing some moderate 15-20 kt westerly 
shear, which has paused its intensification for the time being. 
However, this shear is forecast to gradual decrease as it begins to 
move more northward, providing an opportunity for the tropical storm 
to strengthen as it approaches Hispaniola. Some weakening appears 
likely once the system moves over Hispaniola, especially if the 
storm moves over the highest terrain in the Dominican Republic. By 
Thursday, Franklin should be back over open waters in the Atlantic 
Ocean and has an opportunity to start strengthening again. However, 
the environment does not appear to be especially pristine, with the 
ECMWF showing more southwesterly vertical wind shear than the GFS. 
For now, its assumed this shear will not prevent slow 
intensification, possibly because the storm should be moving in the 
same direction as the shear vector, and the NHC intensity forecast 
will still show Franklin becoming a hurricane towards the end of the 
forecast period. This forecast is in best agreement with the HFIP 
corrected consensus approach (HCCA) but remains lower than some of 
the more aggressive regional-hurricane models (COAMPS-TC, HWRF).
 
 
KEY MESSAGES:
 
1. Heavy rainfall from Franklin is expected across portions of
Puerto Rico and Hispaniola through the middle of the week.  The
heavy rainfall may produce areas of flash and urban flooding as well
as river rises and mudslides.  Across Hispaniola, significant and
potentially life-threatening flash flooding is possible Tuesday into
Wednesday.
 
2. Franklin is expected to bring tropical storm conditions to
portions of the Dominican Republic and Haiti beginning on Tuesday
where Tropical Storm Warnings are in effect.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/1500Z 15.0N  70.1W   45 KT  50 MPH
 12H  22/0000Z 15.2N  70.5W   45 KT  50 MPH
 24H  22/1200Z 15.7N  71.0W   50 KT  60 MPH
 36H  23/0000Z 17.3N  70.9W   55 KT  65 MPH
 48H  23/1200Z 19.2N  70.6W   45 KT  50 MPH...INLAND
 60H  24/0000Z 21.2N  69.9W   45 KT  50 MPH...OVER WATER
 72H  24/1200Z 22.8N  68.4W   55 KT  65 MPH
 96H  25/1200Z 24.4N  65.2W   65 KT  75 MPH
120H  26/1200Z 26.4N  63.7W   75 KT  85 MPH
 
$$
Forecaster Papin
 
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