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Tropical Depression Don


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BOTH NOAA AND AIR FORCE RECONNAISSANCE PLANES HAVE BEEN INVESTIGATING TROPICAL STORM DON AND FOUND THAT THE CYCLONE HAD JOGGED TO THE WEST DURING THE PAST FEW HOURS AND THAT THE CYCLONE IS A LITTLE BIT STRONGER. THE MINIMUM CENTRAL PRESSURES REPORTED BY NOAA AND AIR FORCE PLANE EARLIER THIS EVENING WERE 996 AND 998 RESPECTIVELY. MORE RECENTLY A HIGHER PRESSURE WAS REPORTED BUT THE DROPSONDE DID NOT HIT THE VERY SMALL CENTER. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB HAVE INCREASED TO 3.0 AND 3.5 ON THE DVORAK SCALE. THE INITIAL HAS BEEN INCREASED TO 45 KNOTS PRIMARILY BASED ON A BELIEVABLE 43-KNOT SFMR REPORT. THE CYCLONE HAS BEEN UNDER THE INFLUENCE OF NORTHERLY SHEAR AND THE LOW-LEVEL CENTER IS STILL TILTED SOUTHWARD WITH HEIGHT AS REPORTED BY BOTH PLANES. SINCE NO SIGNIFICANT DECREASE OF THE SHEAR IS ANTICIPATED AND THE CYCLONE IS INTERACTING WITH DRY AIR OVER THE WESTERN GULF OF MEXICO...ONLY A SMALL AMOUNT OF STRENGTHENING IS FORECAST BEFORE LANDFALL. IN FACT NONE OF THE GUIDANCE SUGGEST IMPORTANT CHANGES IN INTENSITY.

Meh, 45/998 mb

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Bummer... the NHC discussion is a bit of a letdown. I guess an 8mb drop between two center passes isn't interesting. In other news it looks like the convection is collapsing again near the estimated center. It was a nice burst from it seems the synoptic conditions don't seem to have changed too much. We'll see what those new convective clusters do to the south of the system.

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Bummer... the NHC discussion is a bit of a letdown. I guess an 8mb drop between two center passes isn't interesting. In other news it looks like the convection is collapsing again near the estimated center. It was a nice burst from it seems the synoptic conditions don't seem to have changed too much. We'll see what those new convective clusters do to the south of the system.

Too bad advisory time didn't coincide with the period of rapidly building convection a couple hours ago... we probably would have had a strong TS on our hands.

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there's a propensity for mesolows to form downshear left in sheared TCs.

Could this be the reason for the jog leftward?

Structure of Highly Sheared Tropical Cyclone Chantel during CAMEX-4

Possibly. I'm not sure if it was a completely new center that formed or whether the original center got pulled into the convective burst. You can get a really quick burst of intensification if you're able to get an intense convective burst to occur really close to the center within the RMW, which is apparently what happened in this case. Gabrielle (2001) and Claudette (2003) were also examples of this. Both of those examples went on to weaken quickly after their temporary intensifications, and I've seen that happen with other strongly-sheared storms as well. This is probably because since the shear is strong, the dry air has open access to the core, and the persistent convective burst has downdrafts that bring that dry air down into the boundary layer and kills everything in a heartbeat. I don't think that'll be the case with Don, though, as the shear isn't anywhere near that strong, but I'm wary of the fact that the dry air may still be having some impact.

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Possibly. I'm not sure if it was a completely new center that formed or whether the original center got pulled into the convective burst. You can get a really quick burst of intensification if you're able to get an intense convective burst to occur really close to the center within the RMW, which is apparently what happened in this case. Gabrielle (2001) and Claudette (2003) were also examples of this. Both of those examples went on to weaken quickly after their temporary intensifications, and I've seen that happen with other strongly-sheared storms as well. This is probably because since the shear is strong, the dry air has open access to the core, and the persistent convective burst has downdrafts that bring that dry air down into the boundary layer and kills everything in a heartbeat. I don't think that'll be the case with Don, though, as the shear isn't anywhere near that strong, but I'm wary of the fact that the dry air may still be having some impact.

Yea the examples you cited are very relevant in this case... latest microwave pass shows a mainly exposed center again. It might pulse back up, but its certainly still fighting the shear and the dry air inflow.

skx3m9.jpg

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I thik my early guess, not a whole lot of science, just a quick glance at trends and models, from a day ago, Matamoros or just South, 60 knots, is actually pretty close. Not in the ddwxman league of instability tropical wather analysts, just a SWAG.

60 knots, maybe a tad high, carried away by the enthusiasm of the pro-mets.

post-138-0-50749400-1311911078.jpg

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