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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Floater - Rainbow Color Infrared Loop
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Bonnie never presented well and is likely not dead. This is the same pattern she has been following. Look dead and then make a comeback. By comeback I mean staying alive. I actually think this is the best she has looked all day. I guess thats not saying much.
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I'll be back
Member Since: July 12, 2008 Posts: 11 Comments: 422
I'd say it is actually probably maintaining strength..... wind wise... but is also POSSIBLY.... opening up.... so even if this thing does open up... ts winds are still quite possible....
Member Since: July 12, 2008 Posts: 11 Comments: 422
Quoting tropicallsu:
Yes, The radar looks as if all the thunderstorm bands are dying off, true, But this is common when the sun sets on most tropical systems, Also the radar is having a hard seeing over the very tall thunderstorm tops as the COC is pulling away, She is not dead, Wee shall see..


WTF are u talking about? Tall tstorm tops?! LOL
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G'Night all.
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Quoting tropicallsu:
Yes, The radar looks as if all the thunderstorm bands are dying off, true, But this is common when the sun sets on most tropical systems, Also the radar is having a hard seeing over the very tall thunderstorm tops as the COC is pulling away, She is not dead, Wee shall see..


Going over the Hill isnt Waning..its just outta view is all.

Folks need to Match up the Sat Rainbow to the Low Level Swirl.

Dats how yas does it dudes..



Things just dont disappear as one wills it.

Thats Crazy casting.

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I was expecting a bit more from bonnie,the way she tried to fight off the ULL,she was a fighter til the end,may she RIP....he,he,he.......
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Yes, The radar looks as if all the thunderstorm bands are dying off, true, But this is common when the sun sets on most tropical systems, Also the radar is having a hard seeing over the very tall thunderstorm tops as the COC is pulling away, She is not dead, Wee shall see..
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This thing is still a depression.... however... is probably very close to dying out completely and if it doesnt do some serious work... the 11 adv may very well be the last
Member Since: July 12, 2008 Posts: 11 Comments: 422
Quoting Levi32:


Yes.

Well in that case we need to prepare for a funeral.
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Quoting StormW:


Ya know, I really don't know or remember, now that you mention it.


Thanks StormW, I'll look because I'm interested. There's way too much emphasis being placed on "invests" these days. What do you think about the so called "Bonnie Burst".....heh heh. Lots of rain in Mobile and vicinity I think. Thanks man.
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What do you all think about the area in the vicinity of Hispanola? Thanks!
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Quoting atmosweather:


Yes but we've seen the W-erlies on the S side of the circulation only extend a few miles out, so we'll have to wait until they go in through the center to see if it is truly open.


Yes, it's still closed but on the edge. Won't take much more weakening to open it right up.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
Dont get to personal with da Storms...they tend to ignore Folks and Gub ments.
Quoting LADobeLady:


It's not just Transocean it was MMS (now BOE) and the USCG for missing that during inspections or turning a blind eye to it. That is the exception on rigs NOT the norm.


I know.
I worked for Chevron outta Venice and Fourchon in the 90's.
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Quoting WeatherNerdPR:

Am I allowed to say that Bonnie is dying?


Yes.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
Quoting Levi32:
Recon finding easterly winds south of Bonnie's center, indicating that the circulation is ill-defined, barely closed, and she may open up into a wave overnight tonight if this keeps up.



Yes but we've seen the W-erlies on the S side of the circulation only extend a few miles out, so we'll have to wait until they go in through the center to see if it is truly open.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting Levi32:
Recon finding easterly winds south of Bonnie's center, indicating that the circulation is ill-defined, barely closed, and she may open up into a wave overnight tonight if this keeps up.


Am I allowed to say that Bonnie is dying?
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Quoting IKE:
There it goes...literally.....




Yep....... I hate using the "RIP" term.... but I believe there is only remnants of what is left of Bonnie!

I put the chances of TD Bonnie regaining storm status at less than 10%.......
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Quoting Patrap:


Thats news to some from the USCG Investigation here,,but a lot of folks been Knowing that since April 23rd.

They screwed da Pooch and Killed 11 men.

And Made a cesspool out the GOM in a Lotta Places.


OMG!
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Recon finding easterly winds south of Bonnie's center, indicating that the circulation is ill-defined, barely closed, and she may open up into a wave overnight tonight if this keeps up.

Member Since: November 24, 2005 Posts: 635 Comments: 26652
local pressure here in srq is 1013.6mb
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Quoting vortextrance:


Is there a wave near Hispanola or is all the convection associated with the ULL? The wave coming off Africa in a couple of days is a monster.
Pple keep calling that area a wave when it's really an upper level trough that's generating the precipitation there. However there is a SAL embedded Twave approaching the Lesser Antilles that may add some interesting moments tomorrow or possibly Sunday as it moves through the E and C Car.

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Quoting Patrap:


Thats news to smote from the USCG Investigation here,,but a lot of folks been Knowing that since April 23rd.

They screwed da Pooch and Killed 11 men.

And Made a cesspool out the GOM in a Lotta Places.



It's not just Transocean it was MMS (now BOE) and the USCG for missing that during inspections or turning a blind eye to it. That is the exception on rigs NOT the norm.
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Quoting atmosweather:


No its mainly just mid and upper level energy associated with the ULL and some upper divergence helping to fuel the storms.


Thanks. I haven't paid hardly any attention to it. Also Bonnie is trying to get some more convection going. Must be out of reach of all the radar's because there should be more there. Not likely to last but who knows with this one.
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Quoting divdog:
they just want to make sure shes not up to any mischief
Recon always makes several passes over the circulation.
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Quoting vortextrance:
Looks like Bonnie will keep doing what she has been doing which is barely hang on. This is unfortunate. It looked like she might just die but no such luck for the northern Gulf coast. Not much threat of significant strengthening. Same story with the dry air and shear. IF nothing else Bonnie has been a very interesting storm.


Bonnie was sneaky. She left the majority of her convection and rain over Puerto Rico and converted herself into a small system to scoot over South Florida. The mets here today said that the torrential rains we experienced were due interaction between the tropical wave that just passed us (Bonnie)and the next one that will come tomorrow. Haven't seen the sun in over a week.
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Quoting IKE:
There it goes...literally.....


Notice the loss of convection as it moves into water...similar to a lot of T-waves this year...
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Quoting P451:
Well, now it's criminal.


-----

Kenner, Louisiana (CNN) -- An alarm system on the Deepwater Horizon had been "inhibited" for about a year before the April 20 explosion that killed 11 workers and started the worst oil disaster in the nation's history, the platform's chief electronics technician testified to a federal panel Friday.

An inhibited mode means sensors for toxic or combustible gases or fire are active and will alert the platform's computer system, but the computer does not trigger an audible or visual alarm, technician Mike Williams told the six-member panel.

Supervisors on the Transocean rig were aware that the alarm system had been inhibited, Williams said.


Thats news to some from the USCG Investigation here,,but a lot of folks been Knowing that since April 23rd.

They screwed da Pooch and Killed 11 men.

And Made a cesspool out the GOM in a Lotta Places.

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Quoting IKE:
There it goes...literally.....

till we meet again
Member Since: July 15, 2006 Posts: 173 Comments: 54268
Some mischief is being detected south of Hispaniola me thinks. Link
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Quoting MiamiHurricanes09:
Recon heading back towards the center.
they just want to make sure shes not up to any mischief
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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.