Bonnie barely alive

By: Dr. Jeff Masters , 12:58 PM GMT on July 24, 2010

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Tropical Depression Bonnie is barely clinging to life. Wind shear of 25 knots and dry air from an upper-level low pressure system over the Gulf of Mexico are taking their toll on Bonnie, which is now just a swirl of low clouds accompanied by a small clump of heavy thunderstorms on the north side of the center of circulation. These thunderstorms are now visible on New Orleans long range radar, and will arrive in coastal Louisiana early this afternoon, well ahead of the center. The Hurricane Hunters are in Bonnie, and have found a much weaker storm with top winds of just 30 mph.


Figure 1. Morning satellite image of Tropical Depression Bonnie. At the time, Bonnie had sustained winds of 30 mph.

Forecast for Bonnie
The current NHC forecast for Bonnie looks good, with the storm making landfall in Louisiana near 9pm CDT Saturday night. According to the latest tide information, this will be near the time of low tide. This will result in much less oil entering the Louisiana marshlands than occurred during Hurricane Alex in June. That storm brought a storm surge of 2 - 4 feet and sustained winds of 20 - 30 mph that lasted for several days, including several high tide cycles. Bonnie will be lucky to be a tropical depression at landfall, and should only create a storm surge of 1 - 2 feet that will come at low tide. This will result in a storm tide level that will inundate land to at most one foot above ground level.

Resources for the BP oil disaster
Map of oil spill location from the NOAA Satellite Services Division
My post, What a hurricane would do the Deepwater Horizon oil spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA's interactive mapping tool to overlay wind and ocean current forecasts, oil locations, etc.
Gulf Oil Blog from the UGA Department of Marine Sciences
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Synthetic Aperture Radar (SAR) imagery from the University of Miami

Elsewhere in the tropics
There are no other threat areas of concern today. The only model calling for possible tropical development in the next week is the NOGAPS model, which predicts a strong tropical disturbance could form off the coast of Nicaragua in the Southwest Caribbean about a week from now.

Next update
The next updates will be by wunderground meteorologists Rob Carver and Shaun Tanner. I'm taking advantage of a break in the tropical action to take a few days away. I'll be back blogging on Friday, at the latest.

Jeff Masters

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2431. Levi32
Quoting atmoaggie:
Over here, in Covington, we had a solid 6 inches in Dec 08. Stuck around for 48 hours, too.

Visible satellite image showed snow cover the next day for us, Hammond, and parts of S central MS.

That, I had only seen in the mountains and upper midwest.


Good to know you folks in NOLA have at least seen the stuff that I have to live with 7 months of the year :)
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Nada... nuttin...



AOI

AOI

AOI

AOI

AOI

TS BUSTED FORECAST ALIBI
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Quoting KoritheMan:


It wouldn't surprise me. At all.


Seems like its always been about 10-15 years for snow while I was in Houston or here in BR.
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Quoting RedStickCasterette:


Having snow was amazing, especially this last time.
Over here, in Covington, we had a solid 6 inches in Dec 08. Stuck around for 48 hours, too.

Visible satellite image showed snow cover the next day for us, Hammond, and parts of S central MS.

That, I had only seen in the mountains and upper midwest.
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Quoting Bordonaro:

For such a large and well equipped County Hospital, JPS is Tarrant counties (Ft Worth, TX) only Level 1 trauma hospital, they only have 2 vascular surgeons. AMAZING!! But there is nothing I can do as a human being to get them to speed up the process.

Believe me, I literally went off on the 5 doctors that took care of me.


Ha I can imagine! Can you go elsewhere or is it best to just wait it out? Seems like the meds you are on can help you hold out, if that makes sense.
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thanks to all for the input,seems more outer bands and stronger storms will be the worst.I lost a home to hurricane lili in oct.2002 when the train came through.scary stuff
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mesovortices in the eyewall are typically associated with intensification. They are similar to suction vortices you see around major tornados. So, while the tornados they spawn are weak, they can move with their parent mesovorticy at speeds equivalent to the hurricane's windspeed. Without an associated tornado, the mesovorticy itself typically causes an uptick of around 10% as opposed to the rest of the storm. Prime example is hurricane Andrew whose destruction occured predominately in swaths. It wasnt until late that these were theorized to have came from mesovortices and associated tornados (it's difficult to prove due to the fact that rotational debris fields are absent in almost all cases and also due to the fact that the storms are rain wrapped)
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Quoting RedStickCasterette:
Quoting KoritheMan:


Southeast Louisiana has been experiencing awful heat indexes. Even by my standards, which are rather high, it's been hot here. Nay, it's been oppressive. We're under a heat advisory as we speak, and heat indeces have been regularly climbing anywhere from 105 to 115F for the last two weeks.

I've even felt somewhat ill during this period, when I've been out in it. :/


Yes! I do get "sick" after being out in the heat. Never could figure it out.


The fact that I'm a heavy soda drinker only adds fuel to the fire. I know I know, that's not the smartest thing to do, but an addiction is an addiction.
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The strongest Tropical Cyclone tornado that I have ever heard of is the F4 that Hurricane Carla (another large, strong storm with many rainbands) put on Galveston Island.
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Quoting MechEngMet:
2394 Atmo: Great Memory Dude! I'm envious.

Yup that's the storm. Some of the better researchers on here could find news articles that may quote the F-x scale of the 'nado...
I have family that still lives in Belle Terre, been there for 35 years.

And you had it right, F3.

As Hurricane Andrew approached Louisiana, an isolated storm on one of Andrew's raindbands spawned a tornado that traveled west-northwestward through Laplace, Louisiana. The tornado damage path was 9 miles long and about 150 yards wide. The tornado was rated F3 on the Fujita damage scale. Damage to homes was more severe in the tornado than hurricane-caused damage to similarly constructed homes in Louisiana. The tornado lasted ten minutes beginning around 8:10pm.

http://www.stormtrack.org/library/damage/andrew.htm
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Quoting atmoaggie:
Heck, we had snow 2 years in a row. could be 10 years, or more, before we see any again...and that would be statistically normal.


Having snow was amazing, especially this last time.
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2418. Levi32
Quoting atmoaggie:
Abstaining from comment on this one on purpose.

But, yeah, MH09 has a good answer.

I'll say this. Rainbands usually have more documented nadoes than any other part of a TC, though tornado counts in eyewall affected areas are not at all reliable when they are usually brief (2 frames of radar 5 minutes apart could miss them entirely) and the TC winds tend to mask the nado damage. See Ivan's rainband nadoes; a number of papers out there about them.


Yeah I can't see very many tornadoes occurring in the eyewall or in close to the main core. The outer spiral bands would sensibly be the most favorable area for tornadoes.
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Quoting 1900hurricane:

Agreed. However, looking at the more prolific tornado-producers (Ivan, Beulah, Francis, etc), they were all larger tropical cyclones with many bands. Therefore, those are the ones that I believe are most likely to be tornado-prolific. Other than that though, it does seem to be more or less a shot in the dark.


I cant speak for Buelah but Frances and Ivan both made landfall from the gulf.. Gulf land fall hurricanes tend to produce tornadic activity on the east side of the storms.
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2416. Levi32
Quoting PowEDier7:
ever been to the tropics, levi?


No.
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2415. Levi32
Quoting chicotman:
thanks for the input on the twisters,Im no met,but I do live 75 miles inland.It seems the tornadic activity gets worse as the land gets higher above sea level?any thoughts?


Probably because of what some were mentioning about increased friction from the land, and some lifting of the air can occur if the terrain gets higher shortly inland, enhancing strong thunderstorm development.
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How many named storms will form in August? You can go and answer at my blog.

Link
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2394 Atmo: Great Memory Dude! I'm envious.

Yup that's the storm. Some of the better researchers on here could find news articles that may quote the F-x scale of the 'nado...
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Quoting PowEDier7:
Oh boy, not good news, then. Thanks Levi. I live in PBC, by the way.


Same here. Definitely not good news.
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2410. viman
Are there any HAM Radio operators on the blog?
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Quoting KoritheMan:


Southeast Louisiana has been experiencing awful heat indexes. Even by my standards, which are rather high, it's been hot here. Nay, it's been oppressive. We're under a heat advisory as we speak, and heat indeces have been regularly climbing anywhere from 105 to 115F for the last two weeks.

I've even felt somewhat ill during this period, when I've been out in it. :/


Yes! I do get "sick" after being out in the heat. Never could figure it out.
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Quoting chicotman:
thanks for the input on the twisters,Im no met,but I do live 75 miles inland.It seems the tornadic activity gets worse as the land gets higher above sea level?any thoughts?


I'm no expert on tornado formation by any means (severe weather is not my forte, at least not yet), but I would theorize that it is due to increased vertical shear caused by the storm's outflow.

Interaction with mid-latitude cyclones and ridges could also severe to enhance tornadogenesis.
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Quoting beell:


But to get back to the original question, lol...I'd have to say, "I don't know!"

So, MH09 had a good answer.
Abstaining from comment on this one on purpose.

But, yeah, MH09 has a good answer.

I'll say this. Rainbands usually have more documented nadoes than any other part of a TC, though tornado counts in eyewall affected areas are not at all reliable when they are usually brief (2 frames of radar 5 minutes apart could miss them entirely) and the TC winds tend to mask the nado damage. See Ivan's rainband nadoes; a number of papers out there about them.
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Quoting Levi32:


Yes the friction theory makes sense. Apparently not a whole lot is known about tornadoes within hurricanes, and I don't think they can predict how many a hurricane will produce at landfall with any skill.

Agreed. However, looking at the more prolific tornado-producers (Ivan, Beulah, Francis, etc), they were all larger tropical cyclones with many bands. Therefore, those are the ones that I believe are most likely to be tornado-prolific. Other than that though, it does seem to be more or less a shot in the dark.
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2405. Levi32
Quoting KoritheMan:
On the subject of landfalling tropical cyclones and tornado formation, it should be noted that tropical cyclones, on average, don't produce tornadoes as strong as those spawned from troughs and their associated cold fronts.


Right, because of the limiting factors in rotation/shear and explosive updrafts.
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Quoting atmoaggie:
I'm with you. I hate all 10.5 months of summer. But that 1.5 months of Fring is awfully nice around here.

Yes! I always say we do not have a fall or spring here in the South. It was the same in Houston.

I remember flying back on the plane from Anchorage, and about crying, the ground was brown and like 80 degrees coming into Houston. I vowed I would move up there, lol.
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On the subject of landfalling tropical cyclones and tornado formation, it should be noted that tropical cyclones, on average, don't produce tornadoes as strong as those spawned from troughs and their associated cold fronts.
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thanks for the input on the twisters,Im no met,but I do live 75 miles inland.It seems the tornadic activity gets worse as the land gets higher above sea level?any thoughts?
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2401. Levi32
Quoting RedStickCasterette:
Quoting Levi32:


And I would probably die in your heat lol. I've never been in 80 degrees outside before. Have no clue what it's like, not to mention the humidity added to it.


Yeah it was awesome up there. I felt "alive" if that makes sense.

The heat and humidity here gets to you.

Amazing the difference in the dry cold in Anchorage vs. the humid cold in Kenai.


For sure....a cold flow in Anchorage comes from the interior mainland, and sometimes means downsloping off the mountains which results in a much drier cold, while the same cold flow comes off the water into Kenai, resulting in more moisture in the air.
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2400. JLPR2
Quoting atmoaggie:
Our very worst heat indexes are days when the
air
is
completely
still.


My worst heat indexes are on days when the wind is blowing from the SE or S, bringing the hot winds from inland, instead of the fresher ocean winds from the NE or E.
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2399. xcool
MechEngMet yeah Small world :)
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Short add-on to my previous post, the increased surface friction from land would also cause the air at the surface to become even further from geostrophic equilibrium than it was over the water, creating more turning towards the center of the tropical cyclone (which also causes the pressure to rise after landfall). With this occurring at the surface and with the more upper levels less affected and closer to geostrophic equilibrium, this may cause a cross-wind, which certainly doesn't hurt in the formation of mesocyclones and tornadoes.
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Quoting Levi32:


And I would probably die in your heat lol. I've never been in 80 degrees outside before. Have no clue what it's like, not to mention the humidity added to it.


Yeah it was awesome up there. I felt "alive" if that makes sense.

The heat and humidity here gets to you.

Amazing the difference in the dry cold in Anchorage vs. the humid cold in Kenai.
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Quoting MiamiHurricanes09:
Not Levi... but I want to try and answer your question and then have Levi correct me, lol.

I believe that the amount of tornadoes matters solely on the tropical cyclone and can not be predicted. Of course with intense cyclones your bound to see tornadoes, but it can not be predicted.
Depends on where you are and where land fall happens in a hurricane... In Florida we tend to have much more tornadic activity when the land fall occurs from the Gulf rather than the Atlantic side. I think tornadoes reside more on the southern east side of the storms. But I do totally agree with your answer that it (with current technology) be predicted....
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2377 Xcool: Roger That! I was on the other side of Dwyer. On Deanne, before Dreux. Do you recall the Skyview? How about 'Boskos'?

Small world huh?
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Quoting MechEngMet:
Regarding Tornadoes and TCs: An otherwise relatively benign storm came through some time in the 90's. Not much damage to speak of, except it spawned a rather large tornado. I think it might have been an F-3 by the damage it did. It (the 'nado) took out almost a complete subdivision of fairly nice homes. I think it hit in St.John parish somewhere West of Kenner. I wish I could recall more.

Perhaps some others on this blog could shed more light from their memories of that event.

The above just to let you know that some TCs can and have shed some awful tornadoes.

Andrew.
LaPlace to Reserve.
Belle Terre subdivision with almost no home unscathed. 6 (?) other subdivisions wiped.
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2393. JLPR2
Quoting KoritheMan:


Another indicator as to just how active this season has been, and will continue to be.


2008 and 2007 reached 70+ inches of rain while 2006 and 2009 stayed at 50inches

Yet 2005 stayed at 50 inches too so I'm not sure its a very reliable indicator. xD
Member Since: September 4, 2007 Posts: 7 Comments: 8733
2392. Levi32
Quoting 1900hurricane:

That sounds good, but it still doesn't explain storms like Beulah, which made landfall while a ridge was building in. That storm produced 115+ tornadoes (as well as a buttload of rain, but that's a different story). I believe that like you said, it takes place more often than not in the spiral bands. To my understanding, tornadoes are rarely observed anywhere other than the right side of a landfalling storm. This is (I believe) because as the spiral bands move inland, the friction of the land slows the air down at the surface while the air above is affected less, creating rotation, like in the image below (ignore the arrows, pretend this is a landfalling tropical cyclone):



Because the outer bands of a tropical cyclone are more convectively driven than the core (somewhat tying into our conversation earlier about lightning in tropical cyclones), their updrafts can cause these cylinders to be picked up and become upright, creating a mesocyclone, like the image shows below:



The storms of the outer bands that do this are now similar to the supercell storms seen in the central United States, and can spawn tornadoes from their mesocyclones (although they are typically weaker than their non-tropical counterparts):


(image credits go to wiki)

Therefore, the tropical cyclones can be inferred to be large, strong tropical cyclones with many outer bands.

But that's just how I see it. The jury is still out on if that is totally correct or not...


Yes the friction theory makes sense. Apparently not a whole lot is known about tornadoes within hurricanes, and I don't think they can predict how many a hurricane will produce at landfall with any skill.
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Quoting JLPR2:
An interesting fact:

Carolina, PR has seen: 53.79in / 1366.3mm of rain until July 25, 2010

Carolina, PR during the entire year of 2009 got up to: 52.92in / 1344.2mm

So we have surpassed last year's precipitation in just 7 months. O.o


Another indicator as to just how active this season has been, and will continue to be.
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Quoting JLPR2:


Yep, ugly, we get to those index too, but being in an island helps, the sea breeze brings the temps down a little.
But heat index in the 100+ is my life from July-September LOL!
Our very worst heat indexes are days when the
air
is
completely
still.
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Quoting StormW:


They can, but it's a lengthy process.


Thanks Storm! Always appreciate your comments.

Aren't you Coast Guard? A person close to me was in the Coast Guard. Heard of TACLET (sp?)?
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2388. Levi32
Well I don't think I have to feel bad, because the NHC doesn't seem to know much about hurricane-produced tornadoes either.

Hurricanes can also produce tornadoes that add to the storm's destructive power. Tornadoes are most likely to occur in the right-front quadrant of the hurricane. However, they are also often found elsewhere embedded in the rainbands, well away from the center of the hurricane.

Some hurricanes seem to produce no tornadoes, while others develop multiple ones. Studies have shown that more than half of the landfalling hurricanes produce at least one tornado; Hurricane Buelah (1967) spawned 141 according to one study. In general, tornadoes associated with hurricanes are less intense than those that occur in the Great Plains (see the Enhanced Fujita Intensity Scale from the Storm Prediction Center's website). Nonetheless, the effects of tornadoes, added to the larger area of hurricane-force winds, can produce substantial damage.


Link
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Quoting Levi32:


That also makes sense, though in the core of a hurricane the winds in the tornado would likely be no faster than the winds of the hurricane itself lol.

You might be surprised. Id like a little more research to be done, but add in the speed of the hurricanes own winds, I wouldnt be surprised if a cat 5 could have an ef4-5 equivalent embedded in the eyewall. the tornado could, itself move as fast as the flow around it (the Hurricanes wind speed) add in the fact that a tornado is inherently spinning, while the west side might experience a lull in activity relatively, the eastern half would see that much uptick. Let's take for example a tornado with it's own winds of 50kt (weak for sure) move it at a speed of 140 knots .. and houston, we have a problem.
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2386. JLPR2
Quoting WeatherNerdPR:
I'm gotta sleep now. -__- See ya tomorrow!


Good night!
Member Since: September 4, 2007 Posts: 7 Comments: 8733
Regarding Tornadoes and TCs: An otherwise relatively benign storm came through some time in the 90's. Not much damage to speak of, except it spawned a rather large tornado. I think it might have been an F-3 by the damage it did. It (the 'nado) took out almost a complete subdivision of fairly nice homes. I think it hit in St.John parish somewhere West of Kenner. I wish I could recall more.

Perhaps some others on this blog could shed more light from their memories of that event.

The above just to let you know that some TCs can and have shed some awful tornadoes.
Member Since: Posts: Comments:
Quoting Levi32:


Severe weather is one of my weaker spots, but tornadoes require a certain amount of wind shear and rotation of an individual supercell thunderstorm to form. That is why hurricanes typically do not have many because there is little wind shear near the core of the storm and the fast rotation of the storm does not allow individual cells to rotate much on their own.

I could be wrong but I believe tornadoes are generally more likely with the outer spiral bands of a hurricane if it is coming ashore under the influence of an upper trough that is recurving it, shearing it, and creating an unstable environment ahead of the storm where the outer bands are encountering upper divergence and colder air aloft from the trough, supporting supercell development.

That's just a guess...

That sounds good, but it still doesn't explain storms like Beulah, which made landfall while a ridge was building in. That storm produced 115+ tornadoes (as well as a buttload of rain, but that's a different story). I believe that like you said, it takes place more often than not in the spiral bands. To my understanding, tornadoes are rarely observed anywhere other than the right side of a landfalling storm. This is (I believe) because as the spiral bands move inland, the friction of the land slows the air down at the surface while the air above is affected less, creating rotation, like in the image below (ignore the arrows, pretend this is a landfalling tropical cyclone):



Because the outer bands of a tropical cyclone are more convectively driven than the core (somewhat tying into our conversation earlier about lightning in tropical cyclones), their updrafts can cause these cylinders to be picked up and become upright, creating a mesocyclone, like the image shows below:



The storms of the outer bands that do this are now similar to the supercell storms seen in the central United States, and can spawn tornadoes from their mesocyclones (although they are typically weaker than their non-tropical counterparts):


(image credits go to wiki)

Therefore, the tropical cyclones can be inferred to be large, strong tropical cyclones with many outer bands.

But that's just how I see it. The jury is still out on if that is totally correct or not...
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I'm gotta sleep now. -__- See ya tomorrow!
Member Since: July 7, 2010 Posts: 0 Comments: 5690
2381. beell
Quoting chicotman:
levi32,will we have more tornadoes involved with the tropical storms this year?


But to get back to the original question, lol...I'd have to say, "I don't know!"

So, MH09 had a good answer.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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