Tropical weather analysis - July 27, 2011

By: KoritheMan , 2:14 AM GMT on July 28, 2011

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Tropical Storm Don formed today over the southern Gulf of Mexico, to the north of the Yucatan Peninsula. As of the 5:00 PM EDT NHC advisory, here was the information on Don:

Wind: 40 mph, with higher gusts
Location: 22.2°N 87.0°W
Movement: WNW at 12 mph
Pressure: 1001 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)

Infrared satellite animations show that Don's northeastern side is getting hammered due to strong northeasterly shear associated with a building ridge over the eastern United States and adjoining western Atlantic. In addition, central convection has warmed substantially over the last couple of hours. This is likely attributable to the usual diurnal convective minimum, which weak systems are inherently susceptible to. There is also a large thunderstorm complex that has recently developed over the northern Yucatan. While this convection is no doubt in part driven by Don, it is probably also being driven by daytime heating over the peninsula. Lastly, cool shallow waters intrinsic to the northern Yucatan Peninsula could also be temporarily halting intensification.

Figure 1. Latest infrared satellite image of Tropical Storm Don, courtesy of NOAA's Satellite Services Division (SSD).

Whatever the case, Don is a relatively disorganized tropical cyclone due to a less than optimal synoptic environment. Consequently, this particular cyclone, like many weak and struggling systems, will be prone to hard to predict center reformations. This could have some implications on both the track and intensity of the system. However, there are no indications of such a reformation currently.

The current ragged nature of the circulation and convection notwithstanding, Don certainly has the potential to slowly intensify up until landfall, and it is still very possible that Don will max out as a minimal hurricane. In fact, I actually expect it to. Anything stronger than 70 kt would be a big surprise though, as conditions simply are not favorable for rapid intensification, with SHIPS calling for steadily decreasing relative humidity values along the forecast track. I have my doubts about this forecast though, since the upper low that was centered over the Bay of Campeche yesterday has now retrograded westward into central Mexico, lessening the dry air. Either way though, whether the SHIPS is correct or not, Don will undoubtedly have some subsidence to compete with. Additionally, upper tropospheric northeasterly to easterly flow appears poised to increase over Don within the 12 hours preceding landfall.

On the plus side, SSTs are very warm, and shear is forecast to remain low through the next 48 hours. Assuming Don can stave off the current environment, he should begin to strengthen. It should be noted that if Don gets north of 25N and west of about 91W, the cyclone will be passing over a warm eddy in the western Gulf of Mexico, which, shear permitting, could allow for some robust intensification within the final hours preceding landfall.

Figure 2. Gulf of Mexico Tropical Cyclone Heat Potential (TCHP) as of July 26, 2011. Notice the aforementioned warm eddy near 25N 92-94W.

The track forecast continues to be characterized by uncertainty until synoptic data from reconnaissance is fed into the models. By tomorrow, we should have a better idea as to the eventual track of this system. Overall though, my own forecast track has not really changed much. The deep-layer ridge over the eastern United States is in the process of rebuilding in the wake of the persistent shortwave trough that has brought beneficial rains to the southeast over the last several days. This, along with a series of weak shortwave impulses forecast to ride the westerlies over the central United States, should induce a general WNW motion to Don, albeit with a slightly more poleward (north) direction to this component initially. A gradual bend back to at true WNW motion should occur late Thursday into Friday. On this track, Don should make landfall near Corpus Christi late Friday afternoon or early evening as a minimal hurricane. It should be noted that if Don stays weaker, a more northern track, toward the upper Texas coast or the Texas/Louisiana border is more likely, as the low-level flow is more poleward in this case.

Interests in the western Gulf of Mexico should closely monitor the progress of Don. It is worth noting that if Don strikes the US as a hurricane, it will be the first actual hurricane strike on the mainland since Hurricane Ike in 2008.

Based on past neutral years, Don should be one of several United States landfalls this year, and I still think we will experience our first major hurricane since 2005 also. Anyone that knows me understands that I do not wish for destruction, but facts are facts and cannot be ignored. Luck can, and will, only hold out for so long. Now would be an excellent time to review your hurricane preparedness plans, as the heart of the season is fast approaching, and future US storms could make Don look like nothing.

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8. TomTaylor
6:47 AM GMT on July 28, 2011
Nice blog, kori
Member Since: August 24, 2010 Posts: 19 Comments: 4358
7. tazzer06
2:53 AM GMT on July 28, 2011
Thanks for the input!
Member Since: May 18, 2010 Posts: 0 Comments: 31
6. Fleetfox
2:39 AM GMT on July 28, 2011
Wow, nice work. Well written. Thanks!
Member Since: July 28, 2011 Posts: 0 Comments: 13
5. Thrawst
2:36 AM GMT on July 28, 2011
Member Since: July 18, 2010 Posts: 50 Comments: 1900
4. bayeloi
2:28 AM GMT on July 28, 2011
Thanks for the update!
Member Since: August 18, 2009 Posts: 0 Comments: 23
3. scott39
2:24 AM GMT on July 28, 2011
Understood it! Great Job!
Member Since: June 13, 2009 Posts: 0 Comments: 6863
2. SouthDadeFish
2:23 AM GMT on July 28, 2011
Good job. I think the recent convective lapse is due to more than diurnal minimum, although that is not helping. Upper-level convergence from the ridge is really doing a number on this thing.
Member Since: August 12, 2007 Posts: 11 Comments: 2448
1. TropicalAnalystwx13
2:23 AM GMT on July 28, 2011
Thanks Kori!

Indications are, the type of activity we've been expecting for the past several weeks, will begin next week.
Member Since: July 6, 2010 Posts: 113 Comments: 32275

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About KoritheMan

I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.

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