[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 242048
TCDAT3

Tropical Storm Franklin Discussion Number  17
NWS National Hurricane Center Miami FL       AL082023
500 PM AST Thu Aug 24 2023

Since the prior advisory, Franklin's appearance has not changed
appreciably, with deep convection continuing to pulse near and to
the east of the low-level circulation center. The last few center
fixes from the earlier Air Force Reserve Reconnaissance mission
showed the tropical storm has continued to turn eastward, though
some of this motion might also be a reflection of the center being
dragged in the general direction of the persistent convective
bursts. The initial intensity for this advisory remains at 50 kt,
out of respect of the earlier aircraft data, and is also close to
the latest UW-CIMSS ADT estimate. Another reconnaissance mission
will be in the storm tonight to provide an updated assessment of
Franklin.

As mentioned above, Franklin is now moving east-northeastward,
estimated at 060/6 kt. This relatively unusual motion for a tropical
cyclone in late August at such low latitude is a byproduct of a
large weakness still parked north of Franklin. This weakness is
thanks in part to a longwave trough, allowing the storm's motion to
be more influenced by a mid-level anticyclone currently located to
its south over the Caribbean Sea. After the next 24 hours or so, the
ridging begins to build in more to the east of the storm, resulting
in both a slowdown and sharp turn north or north-northwestward
between 24 to 48 hours. From there, Franklin takes a much more
climatological motion northward and then recurves
north-northeastward as it is steered between the subtropical ridge
to its west and a amplifying mid-latitude trough digging into the
Great Lakes region by the end of the forecast period. While there
remains some cross-track spread in the track guidance solutions as
Franklin makes its turn northward, both the latest ECMWF and GFS
solutions have closed the gap between their tracks, and the latest
NHC track only needed minor adjustments compared to the prior cycle.

As discussed this morning, Franklin is expected to slowly intensify
for the next 24-36 h as moderate vertical wind shear is expected to
be somewhat offset by warm 29-30 C sea-surface temperatures. After
Franklin makes its turn northward, a cutoff low is expected to drop
southwest of the storm, placing it in a more favorable upper-level
difluent flow pattern. The guidance this cycle is showing a bit
faster rate of intensification early on, so the intensity forecast
was raised slightly from 48-72 h, still showing a peak intensity
just shy of major hurricane intensity. This forecast is now in good
agreement with the HCCA corrected consensus aid, but is lower than
the more aggressive HAFS-A/B regional hurricane model forecasts.


FORECAST POSITIONS AND MAX WINDS

INIT  24/2100Z 22.4N  68.9W   50 KT  60 MPH
 12H  25/0600Z 22.6N  68.1W   55 KT  65 MPH
 24H  25/1800Z 23.1N  67.0W   55 KT  65 MPH
 36H  26/0600Z 23.5N  66.6W   60 KT  70 MPH
 48H  26/1800Z 24.3N  66.5W   70 KT  80 MPH
 60H  27/0600Z 25.6N  67.1W   80 KT  90 MPH
 72H  27/1800Z 27.3N  67.7W   95 KT 110 MPH
 96H  28/1800Z 31.0N  68.3W   95 KT 110 MPH
120H  29/1800Z 35.4N  66.5W   85 KT 100 MPH

$$
Forecaster Papin
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