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By: louisianaboy444, 7:16 PM GMT on August 11, 2013
Hello, This is your Tropical Update for Sunday, August 11, 2013.
After a lull in the tropics it appears we may have something brewing in the Western Caribbean or southern Gulf of Mexico as we head through this coming week and weekend. There will be a tropical wave moving through the Caribbean this week approaching the Yucatan as we approach Thursday and Friday. The GFS predicts a nice anticyclone over the system at this time and with the help of warm waters and a moist environment closes off a low at 96 hrs.
Figure 1: 12Z GFS 200-850mb Shear hr: 96
It then appears to drift over the Yucatan and into the southern parts of the Gulf of Mexico. The 12Z CMC has the storm forming a little further to the west in the Bay of Campeche, which could become important.
Figure 2: 12Z GFS 500mb Height Anomalies hr: 120
Figure 3: 12Z CMC 500mb Height Anomalies hr: 120
The two figures above are the 500mb height anomalies on both the 12Z GFS and 12Z CMC at hour 120. Both model is showing a trough/weakness over the south-central United States at this time frame. This would be the weakness that would pull any system to the south northward into the central Gulf coast. With the lower heights over the southeast and the sub-tropical high in the SW Atlantic, the pressure gradient will be highest further of to the east. This means that the northerly flow towards the Gulf would be strongest near the Yucatan. For this reason the GFS seems to be a little quicker in taking this storm towards the Gulf Coast while the CMC, being further west in the BOC, seems to meander the storm slowly to the NW. This timing difference will be critical in the final result.
Figure 4: 12Z CMC 500mb Height Anomaly hr: 168
Figure 5: 12Z GFS 500mb Height Anomaly hr: 168
The figures above are the 12Z GFS and 12Z CMC 500mb height anomalies for the period of 168 hrs out. You can clearly start to see the differences. The Canadian has the 594dm sub-tropical height right off the coast of Florida building westward. The GFS shows this high centered a bit further to the north and east. If the CMC verifies, this building high from the east would cause the mean flow to turn from northerly to WNW and would most likely steer the storm into South Texas. The GFS also has the ridge building into the Gulf but as you can see on the graphic below it really does not matter because the storm is already inland at this point
Figure 6: 12Z GFS MSLP Anomaly hr:168
So the main difference between these models appear to be timing and the strength/placement of the sub-tropical high over the Atlantic. If the GFS verifies this storm would most likely catch the weakness to the north before the ridge builds westward. If the CMC verified then this storm would meander a bit longer in the SW Gulf before getting shoved into Mexico. Because of the lower height anomalies over the Southern United States, I do not believe the Texas Ridge will be a huge player here. It will all come down to timing and the position of the sub-tropical ridge. More updates to come!