Bonnie weakens to a tropical depression

By: Dr. Jeff Masters , 8:40 PM GMT on July 23, 2010

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Tropical Depression Bonnie is nearing the end of its traverse of South Florida, and passage over land has significantly disrupted the small storm. Satellite images show almost no heavy thunderstorms near Bonnie's center of circulation, and the center is now exposed to view. Radar-estimated rainfall from the Key West radar shows that Bonnie dumped very little rain on South Florida--maximum rainfall amounts from the storm were about four inches over a small region southwest of Miami. Water vapor satellite loops show that Bonnie is embedded in a large area of dry air, thanks to an upper level low to the west over the Gulf of Mexico. This low has brought an increasing amount of wind shear to Bonnie today, and shear has increased from 20 knots this morning to 25 knots this afternoon. Surface observations in South Florida currently don't show any tropical storm force winds. Bonnie's top winds today were at Fowey Rocks, which had sustained winds of 46 mph, gusting to 53 mph, at 10:45 am EDT.


Figure 1. Satellite image of Bonnie from NASA's MODIS instrument, taken at 17:10 UTC July 23, 2010. Image credit: NASA/.

Track Forecast for Bonnie
The latest set of model runs from 8am EDT (12Z) are very similar to the three previous sets of runs, and this degree of consistency gives me confidence that Bonnie will stay within the cone of uncertainty depicted on the track forecast images. The projected track will take Bonnie over the oil spill region, and the storm's strong east to southeasterly winds will begin to affect the oil slick on Saturday morning. Assuming Bonnie doesn't dissipate over the next day, the storm's winds, coupled with a likely storm surge of 2 - 4 feet, will drive oil into a substantial area of the Louisiana marshlands. However, the current NHC forecast has Bonnie 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. The latest oil trajectory forecasts from NOAA (Figure 2) predicts potential oil impacts along a 150-mile stretch of Louisiana coast on Sunday.


Figure 2. Oil Trajectory forecast for Sunday for the Deepwater Horizon oil spill. Image credit: NOAA.

Intensity Forecast for Bonnie
Bonnie has been disrupted by its passage over land, and it will take at least six hours for the storm to reorganize once it moves over the warm waters of the Gulf of Mexico tonight. This process will be hindered by the large upper-level low to its west. If the low remains in its present location, relative to Bonnie, it will bring high wind shear of about 20 - 30 knots to the storm. This will allow for only slow intensification, or may even destroy Bonnie. Bonnie is unlikely to intensify to more than a 50 mph tropical storm, and I give a 30% chance it will dissipate over the Gulf of Mexico before making landfall. The GFDL model predicts Bonnie could hit the Gulf Coast as a 50 mph tropical storm, but the other major models such as the HWRF, GFS, ECMWF, and NOGAPS show a much weaker storm. I don't give Bonnie any chance of becoming a hurricane. NHC is putting the odds of Bonnie being a hurricane at 2 pm Saturday at 4% (5pm advisory.)

If you are wondering about the specific probabilities of receiving tropical storm force winds at your location, I recommend the wind probability product from NHC. The latest probabilities of various locations getting tropical storm force winds, 39 mph or higher, from the 5pm EDT advisory:

Buras, LA 30%
New Orleans 28%
Mobile, AL 37%
Pensacola, FL 30%

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

Next update
I'll have an update Saturday morning.

Jeff Masters

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I need a trained monkey to click "refresh" so
my finger doesn't get worn out,lol..(Sorry,PETA)
Member Since: Posts: Comments:
Quoting IKE:


LMAO.....




LOL I had sprite through my nose on a couple of those "visits" earlier.
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1959. tkeith
Quoting IKE:


LMAO.....


Hmmm...RI?

*rolls eyes*

there is not even a breeze here Ike...
Member Since: November 1, 2004 Posts: 25 Comments: 8937
Quoting IKE:


LMAO.....




LOL did you save that quote? LOL.
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Quoting atmosweather:


Ideally yes, but it can still be beneficial if it isn't...in this situation though, you can see that the ESE-erly winds along the S side of the upper level ridge (the barbs just W of S FL) are converging with the S-erly winds associated with the E side of the ULL. This creates upper level convergence, which prevents outflow.


Ohhhh I get it now! I was thinking Bonnie's SW side but I see what you mean with the ULL and then the ridge. She is being squeezed.
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1956. IKE
Quoting hurrkat05:
PATRAP WE GOT A STORM ON OUR HANDS THE ULL IS MOVING INLAND IN TEXAS AND ITS NOT AFFECTING BONNIE NO MORE ...SHEAR IS NADA OVER BONNIE..


LMAO.....





Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting RedStickCasterette:


So it has to be on top of the storm, or otherwise it can shear it, like with Bonnie?


Ideally yes, but it can still be beneficial if it isn't...in this situation though, you can see that the ESE-erly winds along the S side of the upper level ridge (the barbs just W of S FL) are converging with the S-erly winds associated with the E side of the ULL. This creates upper level convergence, which prevents outflow.
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Quoting atmosweather:


Yes exactly...an upper level anticyclone on top of a storm gives the storm outflow channels to let it "breathe" and prevents strong upper level winds (shear) from blowing the cloud tops away from the circulation.


So it has to be on top of the storm, or otherwise it can shear it, like with Bonnie?
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Quoting atmosweather:


Well it's all getting dragged out to the NW because the upper level flow is coming strongly from the SE. Meanwhile the low level circultion is continuing WNW-ward thanks to the low level flow around the S-ern side of the ridge to the N of her.


Oops meant NW but looked like the ULL was affecting her from the SW on that loop.
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Quoting RedStickCasterette:


So that's why people say its a good thing for the storms to have an anticyclone over them?

Wow that ULL booked it! Why such a hurry? lol. Bonnie seemed like she was attached to it or it was a magnet.


Yes exactly...an upper level anticyclone on top of a storm gives the storm outflow channels to let it "breathe" and prevents strong upper level winds (shear) from blowing the cloud tops away from the circulation.
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1951. xcool
:)
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting RedStickCasterette:


Ahh so that's why everything is blowing to the NE? Appears that way to me, at least.


Well it's all getting dragged out to the NW because the upper level flow is coming strongly from the SE. Meanwhile the low level circultion is continuing WNW-ward thanks to the low level flow around the S-ern side of the ridge to the N of her.
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Quoting atmosweather:


Yes they can if the tropical system is placed in just the right place in relation to the ULL. Check out the current shear map...notice over the Yucatan, SE of the ULL, that the shear is very low there. That is where Bonnie would have to be to have any chance of significant strengthening...SE of the ULL as the ULL backs away W-ward. This provides a great ventilation system for the storm and creates anticyclonic flow in the upper levels...further helping the storm to draw in more heat energy from the lower levels.


So that's why people say its a good thing for the storms to have an anticyclone over them?

Wow that ULL booked it! Why such a hurry? lol. Bonnie seemed like she was attached to it or it was a magnet.
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Quoting RedStickCasterette:


It looks like she's being squeezed. Awe, makes me sad lol in a way since I have watched her since she was the Walmart wave off Africa, but am glad that no one got hurt and nothing bad here.

Sounds bi-polar, I know, lol.


Ahh so that's why everything is blowing to the NE? Appears that way to me, at least.
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Quoting RedStickCasterette:


Can't they be beneficial to a system at some point?


Yes they can if the tropical system is placed in just the right place in relation to the ULL. Check out the current shear map...notice over the Yucatan, SE of the ULL, that the shear is very low there. That is where Bonnie would have to be to have any chance of significant strengthening...SE of the ULL as the ULL backs away W-ward. This provides a great ventilation system for the storm and creates anticyclonic flow in the upper levels...further helping the storm to draw in more heat energy from the lower levels.
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Quoting xcool:
huh wal mart ?


Yes, she was the Walmart wave, or part of it, if I am not mistaken. Been watching...

Correct me if wrong.
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Quoting texascoastres:
they have all popped back pretty good. Bolivar, Crystal Beach and those are still in the process


That's good to hear. Talked to a family member not long ago that said her friend still goes out to Crystal Beach, where she grew up, and "mourns". That is so sad.

Makes you wonder about wishcasters. Ugh. Yes, storms are exciting to watch and learn about but not worth it once they hit.
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1944. xcool
huh wal mart ?
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting RedStickCasterette:


It looks like she's being squeezed. Awe, makes me sad lol in a way since I have watched her since she was the Walmart wave off Africa, but am glad that no one got hurt and nothing bad here.

Sounds bi-polar, I know, lol.


LOL we all like to gaze at them for a while! And yes that's exactly right...the circulation is getting squeezed by the upper level flow and any convection that tries to develop is getting attacked by the dry air and dragged away from the low level spin by shear.
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Quoting atmosweather:


ULL's are pretty common throughout the early part of hurricane season since energy from the upper troughs associated with the subtropical jet will ride counterclockwise around the troughs and create vorticity in the upper levels...which creates the upper level system.


Can't they be beneficial to a system at some point?
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Quoting atmosweather:
The RGB loop is a good illustration of the upper level convergence that is prohibiting any convective organization. Look at the flow from the S side of the ULL feed moisture from the BOC NNE-ward towards the circultion and then you can see the mid/upper level dry layer advancing W-ward towards the circulation from the other side while all of the cloud tops get sheared NW-ward. This is an almost impossible environment for a decoupled system to reorganize in.


It looks like she's being squeezed. Awe, makes me sad lol in a way since I have watched her since she was the Walmart wave off Africa, but am glad that no one got hurt and nothing bad here.

Sounds bi-polar, I know, lol.
Member Since: Posts: Comments:
they have all popped back pretty good. Bolivar, Crystal Beach and those are still in the process
Member Since: Posts: Comments:
Quoting RedStickCasterette:


That ULL was amazing to watch. Is that normal?


ULL's are pretty common throughout the early part of hurricane season since energy from the upper troughs associated with the subtropical jet will ride counterclockwise around the troughs and create vorticity in the upper levels...which creates the upper level system.
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Quoting texascoastres:
I got no damage, houses on both sides got some. Seabrook, Kemah, Shoreacres, Laporte, BayCliff, San Leon all got it pretty bad. Bolivar, Crystal Beach, Gilcrest and High Island got basically wiped out. Check bac with ya'll when I get to work


Wonder how an old ex of mine fared in Seabrook.

Use to work in LaPorte. Of course that's only across the bridge from Baytown. I miss Kemah and the boardwalk. I hope it has rebuilt?

I've been to Houston and Baytown since but not down in those areas yet.
Member Since: Posts: Comments:
The RGB loop is a good illustration of the upper level convergence that is prohibiting any convective organization. Look at the flow from the S side of the ULL feed moisture from the BOC NNE-ward towards the circultion and then you can see the mid/upper level dry layer advancing W-ward towards the circulation from the other side while all of the cloud tops get sheared NW-ward. This is an almost impossible environment for a decoupled system to reorganize in.
Member Since: Posts: Comments:
I got no damage, houses on both sides got some. Seabrook, Kemah, Shoreacres, Laporte, BayCliff, San Leon all got it pretty bad. Bolivar, Crystal Beach, Gilcrest and High Island got basically wiped out. Check bac with ya'll when I get to work
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Quoting atmosweather:


Night homelesswanderer :) We'll keep her in check! And the ULL will too...LOL!


That ULL was amazing to watch. Is that normal?
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Thanks y'all. Ok I'm really going this time. :)
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Everyone have a good morning! tume to go to work. would rather be here!
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Quoting texascoastres:
Nice to meet you. I live in Hitchcock/Santa Fe just outside Galveston My name is Linda !!


Did ya'll get alot of damage from Ike? I know family and friends had no power for two weeks in Baytown which is further inland. I hear/see pix that Crystal Beach was wiped out. Horrible!

How did Seabrook and Kemah do?
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1931. xcool
:0
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting homelesswanderer:
Well all thanks for a nice relaxing chat I enjoyed it and learned a few things along the way. Not a bad way to spend an evening. :) Naturally I gotta go to sleep. So everything will happen while I sleep as usual. Lol. Hope Bonnie has no nasty tricks up her sleeve. Night everyone. :)


Night homelesswanderer :) We'll keep her in check! And the ULL will too...LOL!
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Quoting homelesswanderer:
Well all thanks for a nice relaxing chat I enjoyed it and learned a few things along the way. Not a bad way to spend an evening. :) Naturally I gotta go to sleep. So everything will happen while I sleep as usual. Lol. Hope Bonnie has no nasty tricks up her sleeve. Night everyone. :)


Nite! Hope she doesn't either!
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Quoting SouthALWX:

sure thing :) Im more active on gulfcoastwx though ;) less BS more weather


I appreciate yours and others discussion tonight/morning. Gets hard to wade through in "normal" hours.

May have to check that site out.
Member Since: Posts: Comments:
Well all thanks for a nice relaxing chat I enjoyed it and learned a few things along the way. Not a bad way to spend an evening. :) Naturally I gotta go to sleep. So everything will happen while I sleep as usual. Lol. Hope Bonnie has no nasty tricks up her sleeve. Night everyone. :)
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Quoting SouthALWX:

sure thing :) Im more active on gulfcoastwx though ;) less BS more weather


I used to post there for a while too...and yeah it's a lot more...on point...LOL! ;) I might stop by there sometime soon.
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Nice to meet you. I live in Hitchcock/Santa Fe just outside Galveston My name is Linda !!
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Quoting atmosweather:


LOL goodnight SouthLAWX...and you did get a little closer IMO so well done ;) But I want a rematch!!! LOL!

sure thing :) Im more active on gulfcoastwx though ;) less BS more weather
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Latest SHIPS no longer shows any intensification before landfall...that means all the statistical and global models now forecast either a tropical depression or a remnant open wave at landfall.
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Quoting texascoastres:
RedStickCasterette ?where do you live?


I am in Denham Springs, outside of Baton Rouge. Moved back here from Texas two years ago. I miss Texas!
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Quoting atmosweather:


It appeared that way if you saw the blob of deep convection but the thing is that the deep convection was not over the surface center and was being dragged to the NW by the SE-erly shear. It was never any better organized than it has been since yesterday morning...it just looked that way on satellite without analyzing it closely.


Sometimes I can see the center, even a naked swirl, on various satellites but seemed I couldn't see hers after she left Florida. Just saw the cute little ball of fire, lol.
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Quoting SouthALWX:

lol I need to get my window ACs back ... I had 3 but my wife felt her mother needed them more than my hurricane supply closet did ... =( ...


Get 'em back! lol
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Quoting SouthALWX:
alright it was nice chatting :) I may be around may not ... I poke my nose in when the trolls and know it alls are away. ( rare now days =( )

good night :) as far as the TC center fix goes .. we'll call it a draw... as in you need to draw your estimates closer to mine in the future ;) haha


LOL goodnight SouthLAWX...and you did get a little closer IMO so well done ;) But I want a rematch!!! LOL!
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RedStickCasterette ?where do you live?
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Quoting TxKeef:
wow, She zoomed right along, she's already near the coast!


She has been zooming, hasn't she?
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Quoting RedStickCasterette:


I don't mind the noise, helps me sleep. We couldn't run any AC on the neighbors but fans did help. Could only pick up local TV since cable was out for quite so time. Was just grateful for light and fans!

I have a window AC here to use, need a generator of course, though but that would be nice next time.

lol I need to get my window ACs back ... I had 3 but my wife felt her mother needed them more than my hurricane supply closet did ... =( ...
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Quoting RedStickCasterette:


To my uneducated (tropically) eyes, it seemed Bonnie might be getting fired up a bit earlier. Now it seems she's getting sheared???


It appeared that way if you saw the blob of deep convection but the thing is that the deep convection was not over the surface center and was being dragged to the NW by the SE-erly shear. It was never any better organized than it has been since yesterday morning...it just looked that way on satellite without analyzing it closely.
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Quoting texascoastres:
Best $433.00 I ever spent. Bought ours after Rita and my husband questioned it but after Ike was glad I did it!


Hmm that's not too bad. I may have to look at prices again. AFTER textbooks and vehicles fixed.
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Quoting SouthALWX:
alright it was nice chatting :) I may be around may not ... I poke my nose in when the trolls and know it alls are away. ( rare now days =( )

good night :) as far as the TC center fix goes .. we'll call it a draw... as in you need to draw your estimates closer to mine in the future ;) haha


Good night. :)
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Quoting SouthALWX:

It's a lifesaver for sure. Loud though ... couldnt afford the whisper ones but when the power is out and Im watching tv in the AC popping pocorn and having a light on ... I dont even notice


I don't mind the noise, helps me sleep. We couldn't run any AC on the neighbors but fans did help. Could only pick up local TV since cable was out for quite so time. Was just grateful for light and fans!

I have a window AC here to use, need a generator of course, though but that would be nice next time.
Member Since: Posts: Comments:
alright it was nice chatting :) I may be around may not ... I poke my nose in when the trolls and know it alls are away. ( rare now days =( )

good night :) as far as the TC center fix goes .. we'll call it a draw... as in you need to draw your estimates closer to mine in the future ;) haha
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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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