Wayward meteorology student on a journey back to the promise land. Aggie. Extreme Weather Junkie. Precipitation Snob. Catholic. Musician. Texan. Nerd.
By: 1900hurricane , 12:46 AM GMT on July 28, 2011
Howdy everybody! It's been quite a while since I've updated my blog, but since we now have Tropical Storm Don in the Gulf of Mexico, it's time to change that! Hurricane hunter aircraft investigated Invest 90L and found that it had organized enough to warrant an upgrade past Tropical Depression status and straight to Tropical Storm Don.
As of 4:00 PM CDT, Tropical Storm Don was located at 22.2*N and 82.0*W, or about 120 miles north of Cozumel, Mexico. Current movement is to the WNW (295*) at 10 kts (12 mph). Winds are sustained at 35 kt (40 mph) and extend outwards 40 kt (45 miles) from the center of circulation. Don can be seen in his current state below in Visible, enhanced Infrared, and Water Vapor imagery, respectively:
The big question is this: Where is Don going???
The National Hurricane Center is predicting Don to move towards the Texas coastline, making landfall sometime around the Friday night/Saturday morning timeframe. Although pretty much anywhere along the Texas coast appears to be fair game, the center of the NHC's cone takes the center of Don just north of and very near Corpus Christi, TX
However, the latest model guidance appears to be trending slightly further to the north. The 12Z Late-Cycle Dynamic Models (generally the most reliable models) take Don somewhere along the Texas coast between Kingsville and Galveston, with an emphasis near the Matagorda Bay/Port O'Conner area.
I should be pointed out that these models were run based off of the 12Z data, which was well before we knew that Don was a tropical storm or where exactly the center of circulation was. This means that some or all of the models were initialized incorrectly, giving out bad data. Notice how the models were all initialized in different places. If they begin running with Don in the wrong place (and at the wrong strength possibly), what makes you think that they will forecast Don to move correctly?
More recently, the 18Z Early-Cycle Dynamic models have been run. The early-cycle models are not as accurate due to the fact that they are simpler than their late-cycle counterparts, allowing them to run faster and be presented sooner. However, by 18Z, there was better and more information to be used in the models, so these have the potential to be more accurate than their late-cycle brethren based off of information six hours older. The 18Z early cycle dynamics can be seen below:
Notice how they all have Don starting from the same place. Presumably the correct place. Also notice how they are more tightly clustered. This means that they are in better agreement with themselves (obviously), so confidence is higher that Don will track within that tightly clustered envelope of forecast paths, between Galveston and Corpus Christi.
The other big question: How strong will Don be???
Currently, the National Hurricane Center has Don topping out as a strong Tropical Storm with winds of 55 kt (65 mph) just before landfall. Their wind forecast can be seen below:
However, this may be a bit conservative. Let's look and see why.
First, sea surface temperatures are very warm the entire gulf is well above the threshold to sustain a tropical cyclone (26.5*C), which can be seen below:
This is also much warmer than average for the Gulf of Mexico, which can be seen in the sea surface temperature anomaly map:
Also of note is that the warm water runs very deep, which means that upwelling will not likely be a factor. This leads to very high oceanic heat contents. The current OHC of the Gulf of Mexico can be seen below.
Something interesting to note is that an OHC of 80 kJ/cm^2 or higher will allow for rapid intensification under ideal conditions. Patches of OHC greater than 80 kJ/cm^2 cover sizable portions of the Gulf. However, are conditions ideal enough to possibly allow for rapid intensification?
Tropical Cyclones cannot strengthen when being influenced by wind shear, or differences of wind velocities with height. When wind shear is present, a tropical cyclone cannot organize or strengthen because the differentials of wind velocities with height prevent a tropical cyclone from consolidating. So, does Don have wind shear in his forecast?
If the models are to be believed, no, Don does not have much shear to worry about. Below are a couple of model forecasts for shear. The forecast time period is 00Z July 29th, or Thursday at 7 pm CDT.
Notice how little shear there is over the Gulf of Mexico during this time. Shear values are expected to be this low during Don't entire crossing of the Gulf, so that seems to be a green light for Don.
However, none of this really means anything if Don isn't sufficiently organized to begin strengthening. Below is a microwave image of Don. Microwave imagry actually has the ability to see through the top of a storm and really look at it's structure and is a very useful tool in tropical meteorology. So, what does Don't current structure really look like? Let's see...
Doesn't look like much, does it? Actually though, it does! Often when a tropical storm first develops, it really is very disorganized structurally. Don's structure is actually very good for a recently named storm, and this could set the stage for future strengthening. Because Don is fairly organized, it doesn't have to spend a ton of time organizing itself down the road and could strengthen fairly quickly once completely organized.
One final factor related to the future strength of Don is his areal size. As of right now, Don is a fairly small storm aerially. Smaller storms have less inertia, and can spin up quicker than a larger storm can. However, it is also worth noting that if something were to interrupt Don (land, wind shear, dry air, etc), he would also be more likely to spin down quicker as well.
So, what does this all mean? My Prediction
Don appears to be in nearly ideal conditions to strengthen and already has a decent core put together, so I expect that as soon as Don gets just a little further away from the Yucatan Peninsula of Mexico, he will begin strengthening. My best guess (as well as the NHC forecast) has Don over the warm Gulf of Mexico for slightly over 48 hours. It also appears that Don is targeting the Texas coast almost exclusively. I would expect Don to make landfall between Corpus Christi and Galveston, TX, although I would not be stunned if Don ended up a little north or south of that area. I feel that Don has enough time over the Gulf of Mexico to make it to Hurricane status and possibly be pushing Category 2 intensity by landfall. Landfall to me looks most likely to me to be early Saturday morning, prior to sunrise and moving inland after that. So my first offical prediction for Don is as follows:
Landfall between Sargent and Port O'Connor, TX. Category 1 Hurricane with winds of 75-80 kt (85-90 mph). Landfall time to be 3ish am (plus or minus a few hours). I expect Don to remain rather small, with tropical storm force winds extending less than 75 miles from the center of circulation. Hurricane force wind should be even less than that, 20 miles or less from the center.
Impact wise, I expect wind damage consistent with tree limbs down and a few shingles lost near the landfall point and slightly to the right of it extending inland 30 miles or so. Otherwise, probably just nuisance wind damage for other areas. Flash flooding may briefly be an issue with heavy rains, but the combination of Don's forward speed and the near-record drought in place over Texas should keep flooding concerns to a minimum. Surge also shouldn't be too bad. The combination of Don's small size and relatively weak strength should keep coastal storm surge to 5 feet or less. Rainfall amounts should average 2-4 inches close to Don's path with isolated totals of 5-8 inches possible. Lesser amounts will be found further from the center. Still though, any rain will be beneficial to Texas because of the drought.
That is my take on Don. Please be sure to check with the National Hurricane Center for up to date information relating to Don's intensity, track, and impacts. I will also be posting updates to this blog in the comments section. Feel free to post any questions, comments, or criticisms you have!
Thanks and Gig 'Em!
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