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
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