[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 290236
TCDAT3

Hurricane Franklin Discussion Number  34
NWS National Hurricane Center Miami FL       AL082023
1100 PM EDT Mon Aug 28 2023

Franklin remains a powerful category 4 hurricane.  Satellite images
show a clear and circular eye with a solid and symmetric ring of
deep convection surrounding that feature.  The Air Force Hurricane
Hunters have investigated Franklin during the past few hours and
found 700-mb flight-level winds as high as 140 kt and maximum
surface SFMR winds of 128 kt.  In addition, the minimum pressure
based on dropsonde data is estimated to be 926 mb.  Based on these
data, the initial intensity is set at 130 kt, which is close to the
upper bound of category 4 status.

The major hurricane is now moving due northward at 9 kt.  A turn to
the northeast is expected on Tuesday, with a steady increase in
forward speed forecast during the next few days as the hurricane
moves in progressively faster flow between a mid-level ridge
over the central Atlantic and a mid- to upper-level trough over the
northeastern U.S. and eastern Canada.  The models are in relatively
good agreement during the next 72 hours, however, they diverge
significantly after that.  The GFS shows a continued acceleration
to the northeast with the trough eventually capturing Franklin.
Conversely, the ECMWF shows the trough pulling away, leaving
Franklin behind in weaker steering currents.  The NHC track forecast
is roughly between those very different solutions, sticking close
to the various consensus aids.

Franklin should maintain its strength overnight, but a steady
weakening trend should begin on Tuesday as the hurricane moves over
progressively cooler waters and into an environment of higher shear.
Regardless, Franklin is expected to be a significant hurricane
during the next few days.  Franklin should complete extratropical
transition in 3 to 4 days when it crosses the northern wall of the
Gulf Stream Current and moves into an environment of very strong
shear.  The NHC intensity forecast is a little lower than the
previous one and close to the HCCA and IVCN models.


KEY MESSAGES:

1. Tropical storm conditions are possible on Bermuda beginning
Wednesday morning, when Franklin is forecast to make its closest
approach to the island.

2. Life-threatening surf and rip currents are occurring along the
coast of the southeast United States. These conditions are
expected to spread northward along the remainder of the U.S.
east coast, Atlantic Canada, and Bermuda during the next couple of
days.


FORECAST POSITIONS AND MAX WINDS

INIT  29/0300Z 29.4N  71.0W  130 KT 150 MPH
 12H  29/1200Z 30.5N  70.8W  130 KT 150 MPH
 24H  30/0000Z 32.1N  69.7W  120 KT 140 MPH
 36H  30/1200Z 33.9N  67.7W  110 KT 125 MPH
 48H  31/0000Z 35.8N  64.5W  100 KT 115 MPH
 60H  31/1200Z 38.0N  60.3W   95 KT 110 MPH
 72H  01/0000Z 40.9N  55.3W   85 KT 100 MPH
 96H  02/0000Z 45.8N  45.9W   70 KT  80 MPH...POST-TROP/EXTRATROP
120H  03/0000Z 52.0N  38.5W   55 KT  65 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi
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