Teenager. Weather aficionado. Soccer fan. Realist. Posts subject to sarcasm. Goal: National Hurricane Center.
By: TropicalAnalystwx13 , 10:23 PM GMT on June 24, 2011
The Atlantic basin as a whole is relatively quiet today - there is an area of thunderstorm activity in the western Gulf of Mexico, part of which is the remains of Beatriz's old vorticity maximum, and is attached to the tail-end of a frontal boundary. The threat for this to development is very minimal, and fairly nonexistent. But, this is a prime example of why things like this need to be watched, they can spin up fast and at anytime of the season, primarily early and late season. Elsewhere, the main focus of attention is an area of disturbed weather in the southwestern Caribbean. Most of the reliable computer models have shown development, but as of the latest run, 12Z, the ECMWF and NGP have dropped it. I believe they will show it come the next run however, the 12Z model run can be a bit screwy sometimes.
Into the Models
The 12Z GFS is farther south than any of its other runs, and a little weaker. By hour 48, or Sunday, the model is predicting a 1007 mb. low pressure area to move into the Yucatan, south of Belize. It then stalls the low pressure area just off the coast and deepens it to 1000 mb. before rising and crossing the coast, emerging in the Bay of Campeche by hour 96, next Tuesday. At hour 126, the GFS shows the low being forced south and dying over land. I personally believe that this particular solution being depicted by the GFS is not plausible, and unlikely at the moment. Next is the CMC. Unlike the GFS, the CMC model does not show any development before the Yucatan, and keeps it weak crossing it. The system emerges between hours 66-72, and the CMC makes it tropical storm Arlene by hour 96. At hour 108, Arlene, possibly nearing hurricane strength, makes landfall near Tampico, Mexico. As I aforementioned, both the ECMWF and NGP have dropped the development of the this system, at least for this particular model run. If we go back to the 0Z run, the ECMWF was showing at least an area of disturbed weather moving into the BOC, and the run before that had what looked like a tropical depression. The NGP's past run featured at least development into a tropical depression, but is interesting on this run, is that the model depicts a storm on the Eastern Pacific side to combine with the one on the Atlantic side over Central America. This I definitely do not see happening, although I do expect to see the ECMWF and NGP pick back up on development, especially once we can get a defined area of low pressure down in the southwestern Caribbean.
Figure 2. 12Z CMC @ 108 hours - Landfall near Tampico, MX.
Figure 3. 12Z GFS @ 126 - Landfall in the south-central Bay of Campeche.
I stated it in the first paragaph of this blog, but I'll repeat it - sometimes the 12Z model runs can be screwy, especially when we are talking about the GFS. For this reason, I am inclined to take these model runs with a grain of salt, and expect to see something more regular show up on the 18Z run. One thing I've noticed is that all the models are showing a farther south track, which keeps the system weaker than what it would be if it further north. My opinion is that the system will move quite a bit north of what the models are showing, emerging in the southern Gulf of Mexico, near 20/21 °N latitude. From there, it will move WNW/W before getting shunted south due to the replacement of a weakness in the eastern Gulf of Mexico by the Texas/Mexico ridge and the Atlantic ridge. A landfall near Tampico, MX, just as the CMC is indicated, seems most likely at this time, although that could change depending on how far south of north the AOI emerges in the BOC/southern Gulf of Mexico. Southern Texas is not out of the woods with this system yet, and they still need to monitor closely over the next couple of days.
Ocean Temps. & Heat Content
As you should know, one of the main reasons this season should not be as active as last is because of the Sea Surface Temperature difference. While we are still above average, we are below that of last years. The same thing can be applied for Tropical Cyclone Heat Potential, it is lower than last years. If we look at the image below, you can see that water temperatures are in the 28-30 °C range, 2-4 °C above what is needed to sustain a tropical cyclone. In the Caribbean, things are not much different; around 3 °C above what is needed to a tropical cyclone to thrive and develop. If we look at the Ocean Heat Content, most of the Caribbean and part of the Gulf of Mexico has enough TCHP to support rapid intensification. However, TCHP is significantly below what it was this time last year in the Caribbean, which is one of the reasons why I do not think we will see much out of our system before making it to the Yucatan. Additionally, once it crosses into the Gulf of Mexico, if it takes the track I am predicting, it will encounter very little Heat content, and cooler Sea Surface temperatures initially. So even if everything else was favorable, our system will not be in the best area to intensify into something more than a tropical storm.
Figure 4. Current Sea Surface temperatures as of 6/24/11.
Figure 5. Tropical Cyclone Heat Potential as of 6/24/11.
Wind Shear & Dry Air
Wind shear and dry air so far this season have been normal to below normal. In the Gulf of Mexico, wind shear values are right around the normal of 20-30 knots. However, in the Caribbean Sea, wind shear has risen to quite a bit above normal. This should change in the first week of July though as the Atlantic basin becomes prime for tropical development. In the dry air department, the Gulf of Mexico has been filled with it because of the extreme heat and sunshine that Texas has experienced so far this spring. But, in the Caribbean, that hasn't been a problem. When we add our Caribbean system into the mix, it seems that both of these will not be a problem. Wind shear in the southwestern Caribbean is moderate to high right now, yes, but an anti-cyclone is forecast to develop and move in tandem with the system as it progresses slowly WNW, lowering wind shear. With the system being so monsoonal in nature and so large, it is possible that it could rid a lot of the Gulf of Mexico of dry air, although it'd probably come back when the system moves out. In summary, our disturbance has favorable conditions, but it still has to struggle with two things, which I will talk about below.
Figure 6. Current wind shear across the Atlantic basin.
Figure 7. Current dry air across the Atlantic basin.
Land interaction & Competition
If you watch Levi32's tropical tidbit videos, you should know that he has talked about the set-up to be favorable for development. But, he has also talked about one of the two factors that may prevent our AOI from becoming a tropical cyclone - land interaction. As I mentioned above, there is currently a break between the Atlantic ridge of high pressure and the Texas/Mexico ridge of high pressure. This weakness should allow for our disturbance to gain a little bit of latitude before it closes off and high pressure dominates once again. Depending on how much latitude the disturbance gains, and where the low pressure area forms, land interaction may be a small problem or a large problem. At this point, it appears that land interaction between Honduras/Nicaragua and our system is inevitable, as our system is moving WNW, and does not have much time to gain latitude - the weakness will only be there for another 48 hours or so. If it does interact with these two locations, it may not get a chance to develop until after it enters the BOC/GOMEX. In that condition, it may not have a chance to become much more than a tropical depression. It should begin to interact with land in roughly 12-24 hours from now if it continued with its current speed.
One of the new problems for our disturbance that has arose is the potential for competition from the Eastern Pacific. There is an area of convection near 90W 10N that is showing signs of rotation, especially on visible satellite imagery. If this system further develops, it may not be a good thing if the Caribbean area wants to develop because it would steal all the convection and available energy. But, if the Caribbean system develops first, it would be vice-versa. It will be interesting see how this turns out nonetheless...Will the Atlantic get TD #1/Arlene? Or will the Eastern Pacific get their third named storm, Calvin?
Figure 8. Eastern Pacific system (left) and Atlantic system (right).
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