Hurricane Franklin Discussion Number  31
NWS National Hurricane Center Miami FL       AL082023
500 AM EDT Mon Aug 28 2023

Franklin has continued to improve in organization during the 
overnight hours. The eye noted in the previous advisory has 
occasionally cleared out on infrared satellite imagery, with the 
cold eyewall temperatures surrounding it cooling to between -65 to 
-75 C in a thick region around the center. Subjective Dvorak 
classifications were both T5.5/102 kt from TAFB and SAB, while 
UW-CIMSS ADT estimates are now as high as T5.7/107 kt. The initial 
intensity was raised to 100 kt at 06 UTC, and that will remain the 
intensity at 09 UTC. While this may be slightly conservative, 
earlier aircraft data showed that the maximum winds were lagging the 
satellite presentation and minimum pressure of the hurricane. This 
intensity still makes Franklin the first major hurricane of the 2023 
Atlantic hurricane season. Another Air Force Reconnaissance mission 
will be in the hurricane this morning to provide an updated 
assessment of the storm.

The hurricane continues to make a gradual turn northward, with the 
latest motion estimate still north-northwest at 335/7 kt. Over the 
next 48 hours the hurricane should continue to turn northward and 
then north-eastward as it rounds the western periphery of a 
subtropical ridge, and very little change was made to the NHC track 
over this time period. After 48 hours, there continues to be 
significant spread, especially in the along-track direction, related 
to how much a mid-latitude trough ejecting out of Canada is able to 
capture the hurricane. The big change this forecast cycle is that 
the ECMWF has come on board showing a trough capture, though it 
still remains slower than the majority of the guidance suite. The 
latest NHC track forecast has thus been adjusted a bit north and is 
quite a bit faster after 48 hours, but is not quite as fast as the 
TCVN and HCCA consensus aids over this period. 

Some additional intensification is anticipated today, as Franklin 
remains in a low shear environment and is over warm 29-30 C 
sea-surface temperatures. The latest intensity forecast still peaks 
Franklin as a Category 4 (115-kt) major hurricane. However, 
inner-core changes, such as eyewall replacement cycles, could occur 
at any time, making it somewhat tricky to pinpoint exactly when 
Franklin will reach peak intensity. After 24 hours, the broadening 
wind field and relatively slow storm motion could make the hurricane 
prone to some local upwelling. In addition, some northwesterly 
shear may also begin to affect the storm. Toward the end of the 
forecast period, more dramatic weakening is possible as the storm 
gets swept up in the mid-latitudes. The latest forecast shows the 
storm becoming a post-tropical extratropical cyclone in 120 h, 
though this could occur sooner than forecasted if the faster 
solutions, like the GFS, pan out.  

The current forecast shows the core of Franklin passing west and 
north of Bermuda in about 60 h, but a tropical storm watch may still 
become necessary later today as its expanding 34-kt wind field to 
the southeast does get close to the island after 48 hours. 

FORECAST POSITIONS AND MAX WINDS

INIT  28/0900Z 27.2N  70.8W  100 KT 115 MPH
12H  28/1800Z 28.3N  71.1W  110 KT 125 MPH
24H  29/0600Z 29.8N  71.0W  115 KT 130 MPH
36H  29/1800Z 31.6N  70.2W  105 KT 120 MPH
48H  30/0600Z 33.2N  68.6W   95 KT 110 MPH
60H  30/1800Z 35.0N  65.7W   90 KT 105 MPH
72H  31/0600Z 37.0N  62.0W   85 KT 100 MPH
96H  01/0600Z 42.0N  53.0W   75 KT  85 MPH
120H  02/0600Z 48.0N  44.0W   65 KT  75 MPH...POST-TROP/EXTRATROP

$$
Forecaster Papin