SATL: POTIRA - Post-Tropical

[AJC3]

The 12Z global models are unanimous in showing a cyclone (STC?) developing in the climatologically preferred area off the SE Coast of Brazil (in this case, south of Rio De Janiero) in 3 days. This would be the equivalent of a late OCT TC/STC in the NHEM.

[Vince_and_Grace_fan]

The 12Z global models are unanimous in showing a cyclone (STC?) developing in the climatologically preferred area off the SE Coast of Brazil (in this case, south of Rio De Janiero) in 3 days. This would be the equivalent of a late OCT TC/STC in the NHEM.

UKMO is the strongest model again, and it looks it develops this into a hurricane. The 12Z GFS today also shows stronger and more tropical-like system (it has symmetrical, moderate warm core on the FSU phase diagram). If the blocking anticyclone south of it will remain strong and sustained, and the cyclone could recurve to west-southwest, it may became an interesting and stronger one.

[TorSkk]

There certainly is some model support for the South Atlantic storm. SSTs are low, 22-25 C

[Vince_and_Grace_fan]

I made a separate topic to this cyclone as it looks like that the development chances are increasing. Some of the models are quite bullish now.

GFS:


ICON (German model):


UK model:


Australian and Korean models (just for curiosity):

[AJC3]

All the globals correctly sniffed this development out several days in advance...

WARNING NR 309/2021
SPECIAL WARNING
ISSUED AT 1600 – SUN - 18/APR/2021
POSSIBLE SUBTROPICAL CYCLONE STARTING AT 191200 WITH CENTRAL PRESSURE 1008 HPA AT 27S 040W, MOVING AT 05 KT TO EAST ASSOCIATED TO CYCLONIC WIND 8/9 WITH GUSTS 10 AFFECTING BRAVO AND SOUTH OCEANIC AREA S OF 25S AND W OF 030W.
VALID UNTIL 200000.

[Nancy Smar]

It has been classified as a subtropical depression by Centro de Hidrografia da Marinha (CHM) at 12Z.

[Subtrop]

WWST02 SBBR 201120
1 31 05 02 12 20
SECURITE
WARNING NR 324/2021
SPECIAL WARNING
ISSUED AT 1030 UTC – TER - 20/ABR/2021
SUBTROPICAL STORM "POTIRA" WITH ESTIMATED CENTRAL PRESSURE OF 1006
HPA AT 26S041.5W, MOVING TO EAST AND AFTER TO SOUTHWEST/SOUTH WITH
ESTIMATED MAXIMUM WINDS 47 KT ON CYCLONE SOUTH SECTOR.
FORECAST: CYCLONIC WIND FORCE 8/10 (34-55 KNOTS) WITH GUSTS WITHIN
100NM AROUND THE CENTER AND WIND W/SW FORCE 7 (28-33 KNOTS) NEAR THE
COAST OVER AREA CHARLIE EAST OF 046W AND AREA DELTA SOUTH OF 21S.
ROUGH/VERY ROUGH SEA ASSOCIATED.
ESTIMATED POSITION:
210000 UTC: 25.1S039.1W - 1006 HPA - ESTIMATED MAXIMUM SUSTAINED
WIND 35-40 KNOTS - SUBTROPICAL STORM
211200 UTC: 24.9S038.2W -1004 HPA – ESTIMATED MAXIMUM SUSTAINED
WIND 35-45 KNOTS - SUBTROPICAL STORM
220000 UTC: 26.2S037.6W -1004 HPA – ESTIMATED MAXIMUM SUSTAINED
WIND 40-50 KNOTS - SUBTROPICAL STORM
221200 UTC: 27.1S037.7W -1000 HPA – ESTIMATED MAXIMUM SUSTAINED
WIND 40-55 KNOTS - SUBTROPICAL STORM
230000 UTC: 27.2S038.6W -1002 HPA – ESTIMATED MAXIMUM SUSTAINED
WIND 40-55 KNOTS - SUBTROPICAL STORM
VALID UNTIL 230000 UTC.

[cycloneye]

 https://twitter.com/JointCyclone/status/1384692368935432192

[TorSkk]

WARNING NR 340/2021
SPECIAL WARNING
ISSUED AT 1200 UTC – WED - 21/APR/2021
SUBTROPICAL STORM "POTIRA" WITH ESTIMATED CENTRAL PRESSURE OF 1006 HPA AT 24.7S037.5W, MOVING TO SOUTHEAST/SOUTH AND AFTER TO SOUTHWEST WITH ESTIMATED MAXIMUM WINDS 47 KT ON CYCLONE SOUTH SECTOR.
FORECAST: CYCLONIC WIND FORCE 8/10 (34-55 KNOTS) WITH GUSTS WITHIN 250NM AROUND THE CENTER. ROUGH/VERY ROUGH SEA ASSOCIATED.
ESTIMATED POSITION:
220000 UTC: 25.6S037.2W - 1006 HPA - ESTIMATED MAXIMUM SUSTAINED WIND 35-50 KNOTS - SUBTROPICAL STORM
221200 UTC: 26S037.6W -1004 HPA – ESTIMATED MAXIMUM SUSTAINED WIND 35-50 KNOTS - SUBTROPICAL STORM
230000 UTC: 27.5S038.5W -1004 HPA – ESTIMATED MAXIMUM SUSTAINED WIND 40-55 KNOTS - SUBTROPICAL STORM
231200 UTC: 27.5S039W -1002 HPA – ESTIMATED MAXIMUM SUSTAINED WIND 40-55 KNOTS - SUBTROPICAL STORM
240000 UTC: 28S040.5W -1002 HPA – ESTIMATED MAXIMUM SUSTAINED WIND 40-55 KNOTS - SUBTROPICAL STORM
VALID UNTIL 240000 UTC.
THIS WARNING REPLACES THE WARNING NR 324/2021.

[Vince_and_Grace_fan]

It seems that the shear will win this battle... again.
The cyclone is still very disorganized, and most of the modell dropped the development chances significantly, so it likely will remain a weak subtropical storm.

It is really interesting how could Catarina win against the shear while any other subtropical or tropical storm didn't (Iba also had a chance to became a hurricane but it got sheared too soon, and Anita was only a short-lived TS too).

[TorSkk]

WARNING NR 355/2021

SPECIAL WARNING
ISSUED AT 1430 UTC FRI - 23/APR/2021
SUBTROPICAL STORM "POTIRA" WITH ESTIMATED CENTRAL PRESSURE OF 1008 HPA AT 25S038W, MOVING TO EAST/SOUTHEAST WITH ESTIMATED MAXIMUM WINDS 35 KT ON CYCLONE SOUTH SECTOR.
FORECAST: CYCLONIC WIND FORCE 7/8 (28-40 KNOTS) WITH GUSTS WITHIN 250NM AROUND THE CENTER AND OVER AREA BRAVO EAST OF 043W. ROUGH/VERY ROUGH SEA ASSOCIATED.
ESTIMATED POSITION:
240000 UTC: 25S037W - 1006 HPA ESTIMATED MAXIMUM SUSTAINED WIND 30-35 KNOTS - SUBTROPICAL STORM
241200 UTC: 26S036W -1006 HPA ESTIMATED MAXIMUM SUSTAINED WIND 30-35 KNOTS - SUBTROPICAL DEPRESSION
250000 UTC: 27S034.5W -1004 HPA ESTIMATED MAXIMUM SUSTAINED WIND 30-35 KNOTS - SUBTROPICAL DEPRESSION
251200 UTC: 28S033.5W -1006 HPA ESTIMATED MAXIMUM SUSTAINED WIND 30-35 KNOTS - SUBTROPICAL DEPRESSION
VALID UNTIL 251200 UTC.
THIS WARNING REPLACES THE WARNING NR 350/2021.

[wxman57]

It seems that the shear will win this battle... again.
The cyclone is still very disorganized, and most of the modell dropped the development chances significantly, so it likely will remain a weak subtropical storm.

It is really interesting how could Catarina win against the shear while any other subtropical or tropical storm didn't (Iba also had a chance to became a hurricane but it got sheared too soon, and Anita was only a short-lived TS too).

Catarina didn't "win against the shear", there was little shear for Catarina. Totally different environment.

[Vince_and_Grace_fan]

Catarina didn't "win against the shear", there was little shear for Catarina. Totally different environment.

Yes, I meant that it could move away from the stronger shear zone which originated from the extratropical stadium and persited east of the cyclone.

[Subtrop]

WARNING NR 356/2021
SPECIAL WARNING
ISSUED AT 1330 UTC - SAT - 24/APR/2021
SUBTROPICAL DEPRESSION "POTIRA" WITH ESTIMATED CENTRAL PRESSURE OF 1006 HPA AT 26S036W, MOVING TO EAST/SOUTHEAST WITH ESTIMATED MAXIMUM WINDS 25/30 KT ON CYCLONE SOUTH SECTOR.
ESTIMATED POSITION:
250000 UTC: 27S034.5W - 1008 HPA – ESTIMATED MAXIMUM SUSTAINED WIND 25-30 KNOTS – SUBTROPICAL DEPRESSION
251200 UTC: 28S033.5W -1008 HPA – ESTIMATED MAXIMUM SUSTAINED WIND 25-30 KNOTS - SUBTROPICAL DEPRESSION
VALID UNTIL 260000 UTC.
THIS WARNING REPLACES THE WARNING NR 355/2021.

[TorSkk]

Warnings have been discontinued