Official Discussion issued by the National Hurricane Center

Katia (AL122023) DATA RELEASED: 9/3/2023 9:00:00 AM UTC

Copy of official data

Tropical Storm Katia Discussion Number   8
NWS National Hurricane Center Miami FL       AL122023
900 AM GMT Sun Sep 03 2023

MET-10 proxy-vis and a series of AMSR2 microwave overpasses indicate
that the surface center is farther south than earlier thought and is
displaced about 170 mi to the south of a small patch of deep 
convection.  Subsequently, Katia has been devoid of convection 
since 0100 UTC, and unless organized deep convection redevelops, 
it will likely be classified as a post-tropical cyclone within the 
next 24 hours.  The initial intensity is lowered to 35 kt and is 
based on a blend of the subjective satellite intensity estimates 
from TAFB and SAB.

The intensity forecast philosophy remains unchanged.  A gradual
spin-down of the cyclone should continue as deep-layer southerly
shear is expected to increase while Katia moves into an inhibiting,
dry and stable surrounding environment.  As a result, The NHC
intensity forecast is similar to the previous one except that it 
now shows Katia degenerating to a remnant low a little sooner, and 
within the next 24 hours.

Katia's initial motion is estimated to be northwestward, or 310/8 
kt.  The cyclone is forecast to move between a large middle- to
upper-tropospheric cut-off low to the west over the subtropical
Atlantic and a northwest-to-southeast oriented mid-level ridge to
the east during the next 36 hours or so.  The picture is more 
explicit through the remaining portion of the forecast than in 
previous global model runs.  As mentioned above, the cut-off feature 
situated west of Katia fills and retrogrades northwestward, while a 
deep-layer mid-latitude trough digs southeastward over the northeast 
Atlantic.  This change in the synoptic steering pattern causes Katia 
to slow to a crawl and gradually turn northward, or meander, on 
Tuesday.  The official track forecast is shifted toward the left of 
the previous advisory to agree more with the tightly clustered 
consensus aids.


INIT  03/0900Z 26.0N  31.9W   35 KT  40 MPH
12H  03/1800Z 26.6N  32.8W   30 KT  35 MPH
24H  04/0600Z 27.1N  33.7W   30 KT  35 MPH...POST-TROP/REMNT LOW
36H  04/1800Z 27.7N  34.3W   30 KT  35 MPH...POST-TROP/REMNT LOW
48H  05/0600Z 28.1N  34.7W   30 KT  35 MPH...POST-TROP/REMNT LOW
60H  05/1800Z 28.5N  34.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
72H  06/0600Z 28.5N  34.2W   20 KT  25 MPH...POST-TROP/REMNT LOW
96H  07/0600Z...DISSIPATED

Forecaster Roberts