[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 210842
TCDAT3

Tropical Storm Franklin Discussion Number   3
NWS National Hurricane Center Miami FL       AL082023
500 AM AST Mon Aug 21 2023

Franklin's cloud pattern has not become significantly better
organized overnight.  The system is producing several clusters of
bursting very deep convection, but convective banding features are
not well defined at this time.  Based on microwave imagery, the
cyclone center is apparently located near the western edge of the
overall convective mass.  The current intensity is held at 45 kt in
agreement with a subjective Dvorak satellite classification from
TAFB.  This value is also supported by objective intensity estimates
from UW-CIMSS.

The storm continues moving generally westward, with a motion
estimate of 270/10 kt.  Franklin's forecast track is somewhat
problematic.  A weakness in the subtropical ridge is expected to
cause the tropical cyclone to turn northward in 24 hours or so.
This should result in Franklin crossing Hispaniola in the 48 hour
time frame.  After moving into the Atlantic, Franklin should turn
northeastward while interacting with a mid-level cyclonic
circulation.  By late in the forecast period, the mid-level cyclone
lifts out which could allow Franklin to turn more to the left.
However there is more than the usual amount of uncertainty in the
3-5 day track prediction, with lots of spread in the model guidance.
The official forecast, like the previous one, is near the middle of
the guidance envelope and close to the model consensus.

The flow on the south side of a broad upper-level trough to the
northwest of Franklin is causing moderate southwesterly vertical
wind shear over the storm.  Dynamical guidance such as the SHIPS
model indicate that Franklin will remain in an environment of
moderate shear for the next several days, and the interaction with
the mountainous land mass of Hispaniola should temporarily disrupt
Franklin's circulation.  The current thinking is that the shear will
not be strong enough to prevent the system from eventually becoming
a hurricane over the southwest Atlantic.  The official intensity
forecast follows the model consensus.


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  21/0900Z 15.0N  69.2W   45 KT  50 MPH
 12H  21/1800Z 15.0N  70.4W   50 KT  60 MPH
 24H  22/0600Z 15.3N  71.1W   50 KT  60 MPH
 36H  22/1800Z 16.7N  71.2W   55 KT  65 MPH
 48H  23/0600Z 18.8N  70.9W   45 KT  50 MPH...INLAND
 60H  23/1800Z 20.9N  70.2W   45 KT  50 MPH...OVER WATER
 72H  24/0600Z 22.5N  69.0W   55 KT  65 MPH
 96H  25/0600Z 24.5N  66.0W   60 KT  70 MPH
120H  26/0600Z 26.0N  64.0W   70 KT  80 MPH

$$
Forecaster Pasch
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