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General Discussion >> The Tropics Today

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cieldumortModerator
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Reged: Mon
Posts: 1068
Loc: Texas 30.40N 97.80W
Alex Implications for Texas This Holiday Week & Weekend
      #87953 - Tue Jun 29 2010 04:51 AM

Tropical Storm Alex as we know has been trending a bit more northerly than anticipated, and as such, starts to compel more consideration of potential impacts on the state of Texas.

When I sat down to start this thread, I believed right away that it was important to note that many of the model runs, and those most based off of some other model doing this, continue to be polluted by feedbacks - and a certain number of them also retain Alex either much too shallow and/or the high pressure to the north quite a bit stronger than current trends necessarily support, or come anywhere close to guaranteeing.

All this suggests that Alex could end up moving a good bit more into Texas than these models still suggest - and not making a complete landfall until later in the week than official forecasts presently advertise (given that they are expecting greater forward speed and/or less water to cross, with an expected northern Mexico landfall).

Another plausible scenario is actually one in which Alex makes landfall somewhere between Brownsville, Tx. and Houston (yes, potentially as far up the Texas coast as Houston).

MORE importantly, regardless of exact point of landfall, odds continue to favor that Alex remains a very large tropical cyclone (think about Ike for a minute) that has a vast expanse of brisk to gale force sustained winds with higher gusts, and an even greater expanse of rain-producing outer bands and rain-producing gulf moisture surges.

This real possibility of a large portion or all of Alex shoving into Texas would be occurring during a week that Texas is already seeing quite a bit of rain... already some in fact part courtesy of gulf moisture surges from Alex.

Should Alex make landfall anywhere left of roughly Victoria & north of San Fernando, Mx. and/or ultimately travel west across the state - - or even worse: over or generally northwestward or northward while west of the Interstate 35 -- even in the case of a much-weakened inland Alex, you would likely see tremendous potential for very copious rains given that Alex continues to be a supremely moisture-laden tropical cyclone. And if the grounds in central/eastern parts of the state do continue to see ongoing showers and storms leading up to such a potential track, the risk of flooding and flash flooding would be extremely high.

It is at least my own personal opinion and experience telling me that the odds of a Texas landfall are at least 1 in 3; and very importantly - the odds that a good percentage of south central and/or east Texas get caught in at least a considerable portion of "the dirty part of the storm" is probably better than 2 in 3 ... At the very least, gulf surges and/or outer bands may be impacting portions of this state which are typically prone to major flash flooding even in a "good year" ... let alone a wet week occurring in a wet year, as we are seeing right now.

Related Links:

Central Texas is known as "Flash Flood Alley" with good reason.

PDF: Tropical Cyclones & Flooding (National Weather Service PDF)

Austin KXAN: More Flash Flooding Education For Texas

Flash Flood Alley 8 sec. video graphic: Flash Flood Alley includes: Del Rio, San Antonio, Austin, Waco, Dallas...

City of Austin: Flood Control


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hogrunr
Weather Guru


Reged: Sun
Posts: 153
Loc: Spring, TX 30.07N 95.51W
Re: Alex Implications for Texas This Holiday Week & Weekend [Re: cieldumort]
      #87960 - Tue Jun 29 2010 10:18 AM

Quote:

Tropical Storm Alex as we know has been trending a bit more northerly than anticipated, and as such, starts to compel more consideration of potential impacts on the state of Texas.

When I sat down to start this thread, I believed right away that it was important to note that many of the model runs, and those most based off of some other model doing this, continue to be polluted by feedbacks - and a certain number of them also retain Alex either much too shallow and/or the high pressure to the north quite a bit stronger than current trends necessarily support, or come anywhere close to guaranteeing.

All this suggests that Alex could end up moving a good bit more into Texas than these models still suggest - and not making a complete landfall until later in the week than official forecasts presently advertise (given that they are expecting greater forward speed and/or less water to cross, with an expected northern Mexico landfall).

Another plausible scenario is actually one in which Alex makes landfall somewhere between Brownsville, Tx. and Houston (yes, potentially as far up the Texas coast as Houston).

MORE importantly, regardless of exact point of landfall, odds continue to favor that Alex remains a very large tropical cyclone (think about Ike for a minute) that has a vast expanse of brisk to gale force sustained winds with higher gusts, and an even greater expanse of rain-producing outer bands and rain-producing gulf moisture surges.

This real possibility of a large portion or all of Alex shoving into Texas would be occurring during a week that Texas is already seeing quite a bit of rain... already some in fact part courtesy of gulf moisture surges from Alex.

Should Alex make landfall anywhere left of roughly Victoria & north of San Fernando, Mx. and/or ultimately travel west across the state - - or even worse: over or generally northwestward or northward while west of the Interstate 35 -- even in the case of a much-weakened inland Alex, you would likely see tremendous potential for very copious rains given that Alex continues to be a supremely moisture-laden tropical cyclone. And if the grounds in central/eastern parts of the state do continue to see ongoing showers and storms leading up to such a potential track, the risk of flooding and flash flooding would be extremely high.

It is at least my own personal opinion and experience telling me that the odds of a Texas landfall are at least 1 in 3; and very importantly - the odds that a good percentage of south central and/or east Texas get caught in at least a considerable portion of "the dirty part of the storm" is probably better than 2 in 3 ... At the very least, gulf surges and/or outer bands may be impacting portions of this state which are typically prone to major flash flooding even in a "good year" ... let alone a wet week occurring in a wet year, as we are seeing right now.

Related Links:

Central Texas is known as "Flash Flood Alley" with good reason.

PDF: Tropical Cyclones & Flooding (National Weather Service PDF)

Austin KXAN: More Flash Flooding Education For Texas

Flash Flood Alley 8 sec. video graphic: Flash Flood Alley includes: Del Rio, San Antonio, Austin, Waco, Dallas...

City of Austin: Flood Control




That is a good read...Can you possibly go into more detail as to what you see that is "polluting" the models, such as the feedback you mentioned?

I am not as skilled at seeing those types of things and am curious as to why Alex has continued it's "out of model" path so to speak.


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cieldumortModerator
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Reged: Mon
Posts: 1068
Loc: Texas 30.40N 97.80W
Re: Alex Implications for Texas This Holiday Week & Weekend [Re: hogrunr]
      #87961 - Tue Jun 29 2010 10:35 AM

Here is a short explanation:

Feedbacks in the form of one model feeding back into its sub-model's runs, potentially reinforcing, if not outright enhancing, existing errors in judgment.

GFS & GFS-based runs are also creating arguably over-emphasized convective feedback in the form of auxiliary MCSs over Texas and over the northeastern GOM/southeastern states ... these often tend to diminish the natural state of things, throwing model forecasts off in terms of intensity, direction, timing, and rainfall locations and amounts.

Modeled building in of a blocking subtropical high looks somewhat more influential than what is actually happening, so far.

Alex is a deeper system than models have generally been capturing, and is being directed to a much greater degree by steering currents that would take the system farther north, before having the opportunity to begin shoving Alex to the left (let alone southwest), than by steering currents that would not have as much of a northern bent, in a less vertical, less deep system.


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hogrunr
Weather Guru


Reged: Sun
Posts: 153
Loc: Spring, TX 30.07N 95.51W
Re: Alex Implications for Texas This Holiday Week & Weekend [Re: cieldumort]
      #87962 - Tue Jun 29 2010 10:42 AM

Ok, that makes sense. Good explanation and I guess I will just have to keep watching Alex to see where he goes!

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cieldumortModerator
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Reged: Mon
Posts: 1068
Loc: Texas 30.40N 97.80W
Re: Alex Implications for Texas This Holiday Week & Weekend [Re: hogrunr]
      #87963 - Tue Jun 29 2010 10:47 AM

Yes.

On that note, I would probably add that with the help of daylight and a few more images, I now think the odds are even closer to 50/50 that Alex makes landfall somewhere between within 20 miles of Brownsville, Tx and roughly Matagorda Bay, and only about 1 in 4 Mexico, and 1 in 4 farther up the coast than even that.


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cieldumortModerator
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Reged: Mon
Posts: 1068
Loc: Texas 30.40N 97.80W
Re: Alex Implications for Texas This Holiday Week & Weekend [Re: cieldumort]
      #87975 - Tue Jun 29 2010 06:31 PM

Possibly a somewhat fortuitous development this afternoon, with Alex now showing signs of veering west sooner than expected. Obviously if this continues, Alex would make landfall south of Texas. However, it is critical to remember that a tropical cyclone is not a precise point, and flash flooding is already underway in central Texas in advance of Alex, mostly due to related moisture surges in advance of Alex interacting with an upper level low and daytime heating.

Should Alex indeed make landfall south of Texas, much of south/central/eastern Texas would still likely remain in the dirty side of the cyclone, with copious rainfalls occurring over relatively widespread areas -- very possibly through the entire rest of the week and into the weekend. Flash flooding could easily become prolific. Finally, it is not yet certain that the bulk of Alex will push into Mexico.


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