Thursday, August 2, 2012

Tropical Depression FIVE Becomes Less Organized; Gulf of Mexico Threatened

Tropical Depression FIVE is disorganized at this time, with satellite imagery showing a jumble of scattered showers and thunderstorms that do not appear to be trying to converge. The center of this depression is characterized by the cluster of showers and storms, with what is likely to be either an extension or the beginning of outer banding to the southwest of the center. Let's take a look at what is affecting the storm right now.

Convergence is the bringing-together of moisture to create showers and storms. This commonly happens near a frontal boundary on land, when air is forced up and creates thunderstorms by a convergence of moisture. This can be applied to tropical systems. Looking at TD-FIVE, we see a large area of fairly weak convergence just north of South America. What I find interesting about this graphic is how the main area of convergence is located to the southwest of the center of the system. This displacement of convergence worries me that any upper air intrusion or dry air attack on the center of the system could quickly defeat any circulation evident.

Lower Level winds are posing an obstacle for significant development at this time, with 30 knots of winds attacking the depression in the lower levels of the atmosphere, particularly from the 950mb level to somewhere in the 700mb level. If a strong tropical system is to develop, one would want these lower level winds to die off to allow more significant storm development in the area.

The image above is of shear tendency over the past 24 hours. In a nutshell, if a tropical system is to form, one would need low values of shearing in order to get the most thunderstorm development. Looking at the chart above, we see about 20 knots of shearing where the depression is forecast to move. This does not pose a horrible challenge, but at the stance the depression is in, this could have an interesting effect on the depression's progress and potential strengthening.
What is more concerning is the shearing to the north of the depression, which is clocked at a strong 40-50 knots. This certainly poses a challenge to any significant formation on the northern flank of the depression, and there will likely not be any development in that area until shearing decreases.

Short range models are projecting TD-FIVE to move nearly westward before gaining a general west-northwest movement that could eventually transition into a northwest motion. Strength forecasts do have the depression waiting a bit before gaining tropical storm status. I agree with this, as there remains issues with development in the depression.

What is much more concerning is the image shown above by the GFS Ensembles (GEFS). The GEFS is showing lines that denote strengths of 1000mb systems of 1040mb ridges. In this case, it is 1000mb. As you can see, there are many circles in the Gulf of Mexico. This denotes the presence of Tropical Depression FIVE, which may very well be a tropical cyclone at this time. Some of the circles are larger than others. This indicates that the ensemble member believes that the storm system will be stronger than other members with smaller circles.
This is extremely concerning, as it presents a clear threat to the Gulf of Mexico with a possible landfall of a tropical system. There appear to be three possible tracks that the GEFS members are taking:

• Texas Landfall
• Mexico Landfall
• Southeast Landfall

Either one of these tracks could have a profound effect on life and property, and all possible options will have to be watched closely.


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