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Tropical Storm Iba Discussion Number 3

Wiki-Hurricanes Forecast Center

6:00 AM AST Sun Mar 24 2019

The cyclone in the South Atlantic has become markedly better organized over the past few hours. Deep convection has exploded near the low-level circulation, and this thunderstorm activity has been accompanied by quite a bit of lightning. In addition, a large and prominent spiral band has taken shape north and east of the low-level circulation. The satellite intensity estimate from SAB was unchanged from the previous advisory; however, this analysis occurred prior to the dramatic changes in appearance we have seen over the past few frames. That change, combined with the fact that the earlier ScatSat pass revealed numerous 30kt wind barbs already, supports upgrading the system to a tropical storm and assigning it the name Iba.

The intensity forecast is fairly tricky, mainly because model spread is large--and in fact has grown since the last advisory. The 0z GFS is now advertising a minimal hurricane, which would make it only the second recorded hurricane on record in the South Atlantic. The 0z ECMWF, meanwhile, has backed off its earlier predictions of intensification and only registers Iba as a weak tropical storm at best. It is unclear what prompted the change in the ECMWF provided that the environment continues to appear conducive over the short term. That being said, the shift in intensity has given me pause in increasing Iba's forecast peak as was originally planned following the completion of the GFS. The storm is still expected to weaken after 72 hours, becoming a post-tropical cyclone the next day. There has been no change in the thinking regarding the track, with a southward drift followed by a curve toward the southeast at an accelerating clip after day three.

FORECAST MAX WINDS

INIT 24/0900Z 35 KT 40 MPH

12H 24/1800Z 40 KT 45 MPH

24H 25/0600Z 45 KT 50 MPH

36H 25/1800Z 45 KT 50 MPH

48H 26/0600Z 40 KT 45 MPH

72H 27/0600Z 35 KT 40 MPH

96H 28/0600Z 30 KT 35 MPH...POST-TROP/REMNT LOW

120H 29/0600Z 25 KT 30 MPH...POST-TROP/REMNT LOW 

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