Subtropical Storm Patty Forecast Discussion

402 
WTNT42 KNHC 020856
TCDAT2

Subtropical Storm Patty Discussion Number   1
NWS National Hurricane Center Miami FL       AL172024
900 AM GMT Sat Nov 02 2024

The low pressure system that the NHC has been monitoring over the 
northern Atlantic has gradually acquired subtropical characteristics 
during the past 12-24 h. The low has become detached from fronts and 
has a shallow warm-core structure, though it remains within a cooler 
airmass behind a cold front over the eastern Atlantic. Despite SSTs 
around 21 deg C, instability aloft has allowed the system to sustain 
some moderate convection that wraps most of the way around its 
center in geostationary and passive microwave images. Since the 
wind field is asymmetric and the system remains co-located with an 
upper-level low, it seems best classified as a subtropical cyclone, 
which is consistent with ST2.5 classifications from TAFB. Thus, the 
NHC is initiating advisories on Subtropical Storm Patty. Earlier 
partial scatterometer data showed 35-40 kt winds in the southern 
semicircle, and the initial intensity is set at 45 kt since it does 
not appear the strongest winds were sampled by the instrument.

Patty is moving east-southeastward at 105/7 kt. The track guidance 
is in very good agreement that Patty will move faster toward the 
east-southeast through early Sunday, bringing the center near or 
over portions of the Azores. Then, a turn toward the east and 
east-northeast is expected through early next week as Patty is 
steered by an upper-level trough. The NHC track forecast lies near 
the center of the guidance envelope, generally between the simple 
and corrected consensus aids.

Little change in strength is expected today, and Patty is forecast 
to be a fairly short-lived subtropical cyclone. This is because 
westerly shear is forecast to increase over the system during the 
next couple of days, which will likely make it difficult for the 
system to sustain convection near and around its center. Due to its 
increasing forward speed, the strongest winds of Patty should 
generally remain over the southern portion of the circulation during 
its lifetime. Given the non-tropical origins of this system, the 
NHC intensity forecast leans more heavily on the GFS and ECMWF 
global models, which lie on the lower end of the guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT  02/0900Z 39.9N  34.4W   45 KT  50 MPH
 12H  02/1800Z 39.1N  31.3W   45 KT  50 MPH
 24H  03/0600Z 38.2N  27.3W   40 KT  45 MPH
 36H  03/1800Z 38.0N  23.3W   35 KT  40 MPH...POST-TROPICAL
 48H  04/0600Z 38.7N  19.1W   35 KT  40 MPH...POST-TROPICAL
 60H  04/1800Z 39.8N  15.2W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  05/0600Z 41.3N  11.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  06/0600Z...DISSIPATED

$$
Forecaster Reinhart