[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 220900
TCDAT3

Tropical Storm Franklin Discussion Number   7
NWS National Hurricane Center Miami FL       AL082023
500 AM EDT Tue Aug 22 2023

Although deep convection has increased overnight in areal extent
with frigid cloud top temperatures of -84 Celsius, Franklin remains
a somewhat disorganized tropical cyclone.  Unfortunately, neither
the METOP-B and C scatterometer passes (both misses) or microwave
data were helpful in determining with confidence the center of
circulation.  Best estimate is near the new deep convective bursts
near the northwest edge of the convective overcast.  The initial
intensity is held at 45 kt for this advisory and is supported by
the TAFB and SAB satellite intensity estimates, and a blend of the
latest UW-CIMSS objective techniques.

The deep-layer flow southeast of a mid-Atlantic trough to the
northwest of Franklin is producing moderate southwesterly vertical
wind shear over the cyclone.  Statistical-dynamical ECMWF and GFS
SHIPS guidance indicate that Franklin will remain in a harsh shear
environment for next several days, and interaction with the higher
mountainous elevations as it traverses Hispaniola should further
disrupt the storm's circulation.  By the weekend, however, the
global models are in good agreement that the upper wind pattern
will become more conducive for strengthening and the official
forecast shows Franklin become a hurricane over the southwest
Atlantic by day 4.

The initial motion is estimated to be an uncertain northwestward
drift at 325/3 kt.  Intermittent deep bursts of convection due to a
moderate deep-layer wind shear environment can induce surface
center reformation, particularly where the coldest cloud top
temperatures and the mid-level circulation center resides. Franklin
should remain in a weak synoptic steering current due to the
previously mentioned high amplitude mid-atlantic trough in the
western Atlantic for the next 12 hours or so.  A subtropical high
eventually builds in to the east of Franklin, which should
induce a northward motion, and then a northeastward track after the
48 hour period.  Toward the end of the forecast period, Franklin is
expected to turn generally northward as a mid-latitude shortwave
pulse moves off of the eastern seaboard on Sunday and strengthens
the weakness over the western Atlantic.  The forecast track lies
between the TVCA simple multi-model consensus the the HFIP corrected
consensus aid, and is slightly faster (along-track spread) than the
previous advisory between the 48 and 72 hour periods.


KEY MESSAGES:

1. Heavy rainfall from Franklin is expected across portions of
Puerto Rico and Hispaniola into Thursday. 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 today into Wednesday.

2. Franklin is expected to bring tropical storm conditions to
portions of the Dominican Republic and Haiti beginning today
where Tropical Storm Warnings are in effect.


FORECAST POSITIONS AND MAX WINDS

INIT  22/0900Z 14.8N  70.3W   45 KT  50 MPH
 12H  22/1800Z 15.7N  70.5W   50 KT  60 MPH
 24H  23/0600Z 17.3N  70.5W   55 KT  65 MPH
 36H  23/1800Z 19.3N  69.7W   40 KT  45 MPH...ALONG COAST
 48H  24/0600Z 21.6N  68.8W   45 KT  50 MPH
 60H  24/1800Z 22.7N  67.7W   50 KT  60 MPH
 72H  25/0600Z 23.2N  66.3W   55 KT  65 MPH
 96H  26/0600Z 23.6N  64.3W   65 KT  75 MPH
120H  27/0600Z 26.3N  64.6W   70 KT  80 MPH

$$
Forecaster Roberts/Pasch
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