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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1661. scott39
Quoting Patrap:
La..La..La



Round 9 Ding Ding-- Bonnie tightened her gloves up!
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Quoting PtownBryan:
Homeless...here is another Ike pic. It looked weird in your pic because of dry air being pulled into it....when I look at the pic below, it blows my mind that Ike was this big. Since the electricity was out and TWC was not available(gotta love the cable co) a day or so before Ike hit, I had forgotten just how big it was.







Hi. Your pic isn't coming through. To m at least. But thanks for solving that mystery for me about the dry air. :) BRB.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
1659. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 129093
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1657. xcool
pat THANKS FOR RADER UPDATE...
Member Since: September 26, 2009 Posts: 2 Comments: 15684
1656. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 129093
1655. Kendrix
Quoting MississippiWx:


Lol. I don't think it's much to really worry about, but it's just pretty fun to watch. I have a feeling it will collapse.


We'll take it! Gotta take 'em as they come and go, but I don't feel we'll be so fortunate for long. A Storm will come through with perfect conditions, always be ready for anything!
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Well good night...all good morning!
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1653. Patrap
La..La..La



Member Since: July 3, 2005 Posts: 426 Comments: 129093
1652. Levi32
Quoting RedStickCasterette:
I had the fortune of visiting Alaska in January of '06. It is truly "God's Country" and yes, I felt like I was breathing pure oxygen once I stepped off the plane in Anchorage. I would love to go back!


We should all have a party up here sometime lol.
Member Since: November 24, 2005 Posts: 635 Comments: 26685
Quoting homelesswanderer:


Yeah. Just looking at that sat shot his weird outer bands were already to the top of Louisiana. That was one big Bubba. He followed us to Longview. Knocked out the power at the motel. Blew the water into the second story. They passed out extra towels to the first floor because the rain flooded. It just got wet on the second floor. He knocked down trees on peoples houses. Incredible!


I just realized something...the strongest hurricane to strike the U.S. in both the 1990s (Andrew) and the 2000s (Charley) passed directly over my house...three decades in a row maybe? LOL!
Member Since: September 24, 2005 Posts: 33 Comments: 9265
1650. scott39
Quoting MississippiWx:


Lol. I don't think it's much to really worry about, but it's just pretty fun to watch. I have a feeling it will collapse.
The convection looks like its expanding right over the NW side of the LLC.
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1649. KEEPEROFTHEGATE (Mod)
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1648. xcool
Snow in LA that all i'm go said beep
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting MississippiWx:


Lol. I don't think it's much to really worry about, but it's just pretty fun to watch. I have a feeling it will collapse.


Hope so. :)
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Quoting TexasHurricane:


yeah...LOL. That is how my son was during Humberto. What was that, what was that,what was that. :)


Lol. Exactly.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
1645. xcool
scott39 .slow down lil bit
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting homelesswanderer:


Oh boy. Watch it.


Lol. I don't think it's much to really worry about, but it's just pretty fun to watch. I have a feeling it will collapse.
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Quoting GBguy88:


If I could, I would trade you a hurricane and 3 months of 90+ heat for a breath of Alaskan air :-) You're fortunate to live in such a beautiful state..

I had the fortune of visiting Alaska in January of '06. It is truly "God's Country" and yes, I felt like I was breathing pure oxygen once I stepped off the plane in Anchorage. I would love to go back!
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Home Grown mischief like this are mostly rather weak like the last few storms as they are more under the influence of shear and things such as the Upper Level Low with Bonnie but don't let your guard down Cape Verde Hurricanes are very different...they collect alot of energy on their voyage and by the time they get in the Caribbean or gulf they are hard to stop with all that potential Energy...With all 3 of our storms being in the gulf this year that could be bad when these small storms get replaced by Cape Verde Systems
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Quoting MississippiWx:
Convection continues to expand.



Oh boy. Watch it.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
1639. Levi32
Quoting louisianaboy444:


So you think this will be a warm winter for the Southeast?


Likely yes, especially after December.
Member Since: November 24, 2005 Posts: 635 Comments: 26685
Homeless...here is another Ike pic. It looked weird in your pic because of dry air being pulled into it....when I look at the pic below, it blows my mind that Ike was this big. Since the electricity was out and TWC was not available(gotta love the cable co) a day or so before Ike hit, I had forgotten just how big it was.





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Quoting neonlazer:
Ah, No need to be an expert to find voricity. Just need this! Vorticities


thanks! i have seen the vorticity maps posted on here lots, but i never knew where they got them
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1636. scott39
Quoting MississippiWx:
In recent infrared loops from NASA, you can see the low-level center being tugged underneath the convective blow-up. Pretty interesting to watch.
That sounds like developement?
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1635. JLPR2
Well Bonnie is trying hard!


Goodnight everyone, lets see what tomorrow, well today... XD brings.
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1634. scott39
Quoting xcool:
Is it an illusion or does she seem to be slowing down a bit?
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Quoting homelesswanderer:


Nope. All the better to freak you out. You can hear everything. But have to imagine what made the noise. Lol.


yeah...LOL. That is how my son was during Humberto. What was that, what was that,what was that. :)
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Snow is the only thing people on here can wishcast for and its okay!
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Quoting angiest:


As Ike was finishing coming onshore at the north end of Trinity Bay, I was an hour north of Dallas getting a little wind and rain from him and the clouds were very obviously from a tropical cyclone (to anyone who has ever been in one).


Yeah. Just looking at that sat shot his weird outer bands were already to the top of Louisiana. That was one big Bubba. He followed us to Longview. Knocked out the power at the motel. Blew the water into the second story. They passed out extra towels to the first floor because the rain flooded. It just got wet on the second floor. He knocked down trees on peoples houses. Incredible!
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Quoting Levi32:


I bet! You guys in Florida had a worse winter than we did lol! I still have pictures of temperature maps of Alaska averaging 5 degrees warmer than most of Florida on several mornings lol.


So you think this will be a warm winter for the Southeast?
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In recent infrared loops from NASA, you can see the low-level center being tugged underneath the convective blow-up. Pretty interesting to watch.
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Quoting truecajun:


thanks. my little eye is not good at spotting vorticity until it's obvious. i use the different loops too. i have been told to use rgb for spin spotting, but i'm still not good at it:(
Ah, No need to be an expert to find voricity. Just need this! Vorticities
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1627. Levi32
Quoting atmosweather:


And I thank my lucky stars I most likely won't have to go through a winter like last years LOL! Unbelievably cold for this far south...and almost never-ending.


I bet! You guys in Florida had a worse winter than we did lol! I still have pictures of temperature maps of Alaska averaging 5 degrees warmer than most of Florida on several mornings lol. We were rather warm last winter.
Member Since: November 24, 2005 Posts: 635 Comments: 26685
1626. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15684
OK GUYS THX FOR THE BLOGGIN IM OUT NIGHT LEVI AND OTHERS PEACE
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Quoting neonlazer:
Only storms, there is no vorticity at and levels south of DR..only north.


thanks. my little eye is not good at spotting vorticity until it's obvious. i use the different loops too. i have been told to use rgb for spin spotting, but i'm still not good at it:(
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Quoting atmosweather:


Yeah that's what people who haven't been through a strong hurricane can't really get their heads around...when the winds are THAT strong for more than about 3 or 4 hours continuously, unless you're sleeping through it, it's just remarkable how insane you feel and how you're just in awe.


I have to admit tho it was cool, until about 3 or 4 am when I wanted to get a lil sleep and as I close my eyes all I hear is that sound...and you know what I am talking about! I sat up in the recliner and said "this is not normal!" LOL.
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1622. scott39
That Sat picture of Bonnie right now, is like looking at a head straight on that is invisible, with a bright orange and red feather sticking straight up and out the left side of her head! LOL-- Is that the right analogy?
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1621. xcool
MississippiWx .wow
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting atmosweather:


And I thank my lucky stars I most likely won't have to go through a winter like last years LOL! Unbelievably cold for this far south...and almost never-ending.


actually snowed here in dade county
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Quoting truecajun:
what's going on south of the Dominican republic?
Only storms, there is no vorticity at and levels south of DR..only north.
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1618. TxKeef
Hey, Hurrkat05 Easy on the caps, you don't have to yell at us.
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Quoting Levi32:


Warm PDO supports cold winters in the SE US like you had this past winter. Cold PDO supports warm in the southeast US. The Pacific northwest, Canada, and Alaska will see the full force of the northern hemisphere winter in 2010-2011.


And I thank my lucky stars I most likely won't have to go through a winter like last years LOL! Unbelievably cold for this far south...and almost never-ending.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting atmosweather:


5 out of 6 for me have been at night...it's not too fun LOL!


Nope. All the better to freak you out. You can hear everything. But have to imagine what made the noise. Lol.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
what's going on south of the Dominican republic?
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Quoting homelesswanderer:
Ike was a weir looking storm. It almost looks like he's wearing a war chief's head dress.




looks like a octupus's tentecal wrapped up lol
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Quoting PtownBryan:


God bless you my friend. 10 hrs was enough for me, cannot imagine 24!!!! I imagine we had sustained winds in the 70-80 mph range for the 10 hrs of Ike..I wish I could remember when Ike really started, I think it was around 1030 that night and all I remember is being outside in the morning and see this little last gust of wid blow through the tree in my front yard and it was over, I think around 8-9 am somewhere in between. And yes, Ike was quite an experience!


Yeah that's what people who haven't been through a strong hurricane can't really get their heads around...when the winds are THAT strong for more than about 3 or 4 hours continuously, unless you're sleeping through it, it's just remarkable how insane you feel and how you're just in awe.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting homelesswanderer:
Ike was a weir looking storm. It almost looks like he's wearing a war chief's head dress.



Woah! That looks amazingly weird. Didn't think Ike looked like that when it made landfall.
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1611. angiest
Quoting homelesswanderer:
Ike was a weir looking storm. It almost looks like he's wearing a war chief's head dress.



As Ike was finishing coming onshore at the north end of Trinity Bay, I was an hour north of Dallas getting a little wind and rain from him and the clouds were very obviously from a tropical cyclone (to anyone who has ever been in one).
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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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