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Tropical Depression Five

As expected, the National Hurricane Center upgraded Invest 97L to a tropical depression this afternoon, our fifth of the season. This system has become much better organized and better defined, as shown in the infrared satellite picture (Figure 1). The center of circulation is clearly evident by the counterclockwise swirl of the clouds. As Bryan posted last night, this system has the potential to be a nasty storm. Currently, the National Hurricane Center is not being quite as aggressive as I am with the intensity forecast. As Bryan mentioned, the models are probably junk right now, but let me go ahead with an explanation anyway. Hold on, this is about to get technical.

Figure 1. Infrared satellite image of TD-5

The current intensity models have this storm slowly strengthening over the next 5 days (Figure 2). The NHC forecast discussion mentions dry air and high shear values as the primary reasons TD-5 will not intesify quickly. Figures 3 and 4 show the current shear analysis and Saharan Air Layer analysis from UW-CIMSS. As you can see, there are high values of shear in front of TD-5 and also some moderately dry air.

Figure 3. Shear analysis from UW-CIMSS. The upper level winds in front of TD-5 are quite strong and would tear TD-5 apart if it were to be there now
Figure 4. Saharan Air Layer analysis from UW-CIMSS. There is some dry air in front of TD-5, although not near as much as there was around Debby earlier this week

Here is where my opinion differs from NHC. The GFS, while most likely wrong about the position of TD-5, shows shear relaxing in front of TD-5. Figure 5 shows the GFS forecast for shear on Saturday morning. This is a very busy figure, however, the important thing to know is that cool colors indicate regions of low shear and hot colors indicate regions of high shear. If you look at the area south of Hispaniola, you will find lower shear. This also happens to be the same location that the GFS is forecasting TD-5 to be Saturday morning. Again, let me emphasize that the GFS is almost assuredly incorrect with its position of Chris. When the next model run comes in, it will be interesting to see where the GFS places TD-5.

Shear forecast from the GFS for Saturday morning. The white L indicates the GFS forecast position of TD-5. Cool colors indicate regions of low shear and hot colors show regions of high shear. TD-5 is forecast to be in a region of low shear Saturday morning.

Anyway, back to my point. If TD-5 is able to maintain itself over the next 24 hours, in my opinion, conditions will become more favorable for development. I am sticking by my prediction from the message board that we will have Hurricane Ernesto by Saturday night. Things are definitely starting to heat up in the Atlantic. Stay tuned to the StormTrack for more.

Posted by Adam Moyer | Permalink