[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 240231
TCDAT5

Hurricane Tammy Discussion Number  23
NWS National Hurricane Center Miami FL       AL202023
1100 PM AST Mon Oct 23 2023

Microwave data from multiple polar-orbiting satellites received
during the last few hours indicate that Tammy still has a
well-organized low- to mid-level circulation, even as its deep
convection is getting sheared northward. The most recent TAFB Dvorak
classification was a 4.0/65 kt, which supports maintaining Tammy as
a hurricane.

While Tammy's future path remains unusually unclear, especially at
the 4-5 day range, very little change was made to the official track
forecast. The hurricane is currently moving north-northeastward, and
it should get steered northward starting in about 2 days as the
hurricane interacts with a mid-latitude trough approaching from the
northwest. The uncertainty in the forecast increases considerably
after that point as Tammy will likely reach a col point in the
steering flow over the western Atlantic. Many models and ensemble
members indicate another mid-latitude trough will cause the cyclone
to begin to accelerate eastward or northeastward. However, it
appears equally likely that Tammy will then turn westward or
southwestward under the influence of a mid-level ridge that
should build behind the second trough. With no clear reason to
support one solution or another, the NHC track forecast is unchanged
for now. It remains near the consensus of the GFS and ECMWF through
about 72 h, and then favors the ECMWF and ECENS mean after that.

Conversely, the intensity forecast appears to be more
straightforward. Most of the intensity guidance indicates that
slight strengthening is possible during the next day or so, as Tammy
gets a convective boost while interacting with an upper-level
trough. However, after about 48 h, it should begin to weaken and
transition to a post-tropical cyclone. Based on simulated satellite
imagery, this process is expected to complete in about 72 h, though
Tammy will likely continue to produce gale- to storm-force winds for
several days thereafter.


FORECAST POSITIONS AND MAX WINDS

INIT  24/0300Z 22.9N  63.1W   65 KT  75 MPH
 12H  24/1200Z 23.6N  62.2W   70 KT  80 MPH
 24H  25/0000Z 24.7N  60.8W   75 KT  85 MPH
 36H  25/1200Z 26.5N  59.2W   75 KT  85 MPH
 48H  26/0000Z 28.5N  58.3W   75 KT  85 MPH
 60H  26/1200Z 30.0N  58.6W   65 KT  75 MPH
 72H  27/0000Z 31.1N  59.7W   55 KT  65 MPH...POST-TROP/EXTRATROP
 96H  28/0000Z 32.0N  62.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  29/0000Z 32.5N  64.0W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster D. Zelinsky
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