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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2011. Asta
Quoting tkeith:
I cant see this having much, if any, impact on the spill area. But I dont blame them for being cautious.

Ehem. 2-4 feet of storm surge with oil can have a devastating impact on people living along the coast of SE LA and MS.
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2009. tkeith
I've enjoyed the video forcasts 03...I hope you keep doin them.
Member Since: November 1, 2004 Posts: 25 Comments: 8912
Quoting atmosweather:


Well the NHC sent out a vortex which means they've somehow found a closed circulation...but from the data given by the HH I don't see it. This is on the edge of being a remnant wave.


LOL there is a cute little swirl there.

Can say Bonnie has her swirl on.

Lack of sleep? lol.
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Quoting sporteguy03:

The pressure has been rising indicating a weakening cyclone, no west winds this is one of the worst TD's I have ever looked at, Ike you may not get much relief today from the heat.


There's hardly even much atmospheric moisture associated with the system anymore.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
1013mb just end it now
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Quoting RedStickCasterette:


Maybe I've just had no sleep yet but why is the NHC still calling for a TS at landfall? Am I hallucinating?

The pressure has been rising indicating a weakening cyclone, no west winds this is one of the worst TD's I have ever looked at, Ike you may not get much relief today from the heat.
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2003. tkeith
Quoting atmosweather:


Well the NHC sent out a vortex which means they've somehow found a closed circulation...but from the data given by the HH I don't see it. This is on the edge of being a remnant wave.
I cant see this having much, if any, impact on the spill area. But I dont blame them for being cautious.
Member Since: November 1, 2004 Posts: 25 Comments: 8912
Quoting RedStickCasterette:
I thought I saw it but wasn't sure.

Gotta quit doubting myself, thanks guys.

So what does all this mean? Nothing? RIP?


Well the NHC sent out a vortex which means they've somehow found a closed circulation...but from the data given by the HH I don't see it. This is on the edge of being a remnant wave.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
I thought I saw it but wasn't sure.

Gotta quit doubting myself, thanks guys.

So what does all this mean? Nothing? RIP?
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Quoting RedStickCasterette:


Where is her center relative to the convection (little bit)? Can you see it? I'm trying...


To the SE...you can see the naked swirl here.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting tkeith:
I'm beginning to doubt that we get any rain at all from this thing here in NOLA...


I was hoping for rain and a nice, cooling-down breeze in BR.
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And then they just put out a vortex...


000
URNT12 KNHC 241047
VORTEX DATA MESSAGE AL032010
A. 24/10:37:20Z
B. 27 deg 23 min N
085 deg 44 min W
C. 925 mb 797 m
D. 28 kt
E. 066 deg 15 nm
F. 143 deg 32 kt
G. 062 deg 24 nm
H. EXTRAP 1013 mb
I. 22 C / 761 m
J. 23 C / 759 m
K. 19 C / NA
L. NA
M. NA
N. 1345 / 9
O. 0.02 / 0 nm
P. AF309 0703A BONNIE OB 08
MAX FL WIND 32 KT NE QUAD 10:29:20Z
SLP EXTRAP FROM 925 MB
Member Since: September 24, 2005 Posts: 33 Comments: 9265
1996. tkeith
I'm beginning to doubt that we get any rain at all from this thing here in NOLA...
Member Since: November 1, 2004 Posts: 25 Comments: 8912
Quoting atmosweather:
Well after going through the center and finding 2 separate areas of pressure minimums (only 1013 mb again)...they can't find W-erly winds.


Where is her center relative to the convection (little bit)? Can you see it? I'm trying...
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Quoting IKE:


They need to downgrade it then....



I agree...I believe this may not be a tropical cyclone anymore.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
1993. IKE
Quoting atmosweather:
Well after going through the center and finding 2 separate areas of pressure minimums (only 1013 mb again)...they can't find W-erly winds.


They need to downgrade it then....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Well after going through the center and finding 2 separate areas of pressure minimums (only 1013 mb again)...they can't find W-erly winds.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
1991. tkeith
I wonder if it's too late to book a tee time...
Member Since: November 1, 2004 Posts: 25 Comments: 8912
Quoting tkeith:
me too...the ULL saved our butts this time, but the season is probably just gettin started.



That ULL was amazing to watch.
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Quoting aquak9:
oh my goodness....now that was a good smile for me. Ike, thanks. Yep, ya gotta keep that quote.

G'morning WU-Bloggers worldwide, good afternoon or something to Aussie if he's lurkin'.


Levi sit back and learn. LOL! Has to be a classic...
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1988. IKE
64 NM south of Dauphin Island,Alabama....

5-day plot - Wind Direction Wind Direction (WDIR): NNE ( 20 deg true )
5-day plot - Wind Speed Wind Speed (WSPD): 7.8 kts
5-day plot - Wind Gust Wind Gust (GST): 9.7 kts
5-day plot - Wave Height Wave Height (WVHT): 1.6 ft

5-day plot - Dominant Wave Period Dominant Wave Period (DPD): 7 sec
5-day plot - Average Period Average Period (APD): 4.5 sec
5-day plot - Mean Wave Direction Mean Wave Direction (MWD): S ( 172 deg true )
5-day plot - Atmospheric Pressure Atmospheric Pressure (PRES): 29.99 in
5-day plot - Pressure Tendency Pressure Tendency (PTDY): -0.02 in ( Falling )
5-day plot - Air Temperature Air Temperature (ATMP): 85.5 °F
5-day plot - Water Temperature Water Temperature (WTMP): 85.5 °F
5-day plot - Dew Point Dew Point (DEWP): 77.4 °F
5-day plot - Heat Index Heat Index (HEAT): 96.6 °F
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1987. tkeith
Quoting RedStickCasterette:


The drama gets old for sure. I learned how to separate the two years ago, lol. You have to on here. The other thing is the patting-oneself-on-the-back. Grow up!

We dodged a bullet here and I am so glad and for the Gulf Coast, Florida too.
me too...the ULL saved our butts this time, but the season is probably just gettin started.

Member Since: November 1, 2004 Posts: 25 Comments: 8912
As everyone wakes up and checks the IR sats and declares the area south of the DR is developing and has LLC they can see...
Look at the ASCATS below....
It is interesting to see the 35knot winds north of the DR however...

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Quoting reedzone:
Amazing how Bonnie is still a TD, should be a wave before landfall, the ULL still stalling, causing 30-40 knots of wind shear right in its path..


Maybe I've just had no sleep yet but why is the NHC still calling for a TS at landfall? Am I hallucinating?
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1984. aquak9
oh my goodness....now that was a good smile for me. Ike, thanks. Yep, ya gotta keep that quote.

G'morning WU-Bloggers worldwide, good afternoon or something to Aussie if he's lurkin'.
Member Since: Posts: Comments:
Here comes RECON again...
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Amazing how Bonnie is still a TD, should be a wave before landfall, the ULL still stalling, causing 30-40 knots of wind shear right in its path..
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Quoting tkeith:
And yes...it's comical....

I like comedies much better than "dramas"...lol


The drama gets old for sure. I learned how to separate the two years ago, lol. You have to on here. The other thing is the patting-oneself-on-the-back. Grow up!

We dodged a bullet here and I am so glad and for the Gulf Coast, Florida too.
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1980. tkeith
And yes...it's comical....

I like comedies much better than "dramas"...lol
Member Since: November 1, 2004 Posts: 25 Comments: 8912
Quoting IKE:


Exactly.

You have to sift through them. There's a lot of good forecasters on here.

And yes...it's comical....



Ike that quote to Levi is hilarious. You need to keep posting it, lol.

Yes there are good folks on here...

Save that quote, lol.
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1978. tkeith


I think the skimmers should get going out to the DWH site while the seas are calm...the'll make better time :)
Member Since: November 1, 2004 Posts: 25 Comments: 8912
1977. IKE
Quoting atmosweather:


Shear is nada!!! =P





.......and so is Bonnie


LOL!

*more coffee on keyboard*
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1976. IKE
Quoting RedStickCasterette:


I wonder sometimes how this blog is kept open. There are great folks on there but so much casting, bs, etc.

It does get comical though...


Exactly.

You have to sift through them. There's a lot of good forecasters on here.

And yes...it's comical....

Quoting hurrkat05:
LEVI SIT BACK AND LEARN..
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:


Shear is nada!!! =P





.......and so is Bonnie
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting IKE:


He'll show up when the next one affects the GOM. Til then, he'll stay away, looking at how ill-defined Bonnie looks.


I wonder sometimes how this blog is kept open. There are great folks on there but so much casting, bs, etc.

It does get comical though...
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1973. IKE
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting atmosweather:


The thing that gets me most is the "YOU ARE WRONG, I HAVE INFORMATION IN FRONT OF ME THAT PROVES MY CASE" posts...yet no information is ever given LOL!


You think that person is crazy or is honestly a troll just trying to stir things up?
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1971. IKE
Quoting RedStickCasterette:


Well, I've watched/read him or her for five years on here. Just seemed so sincere this time with Bonnie, lol. Never gives any data or proof, though.

I do wonder if "it" is more that one person.


He'll show up when the next one affects the GOM. Til then, he'll stay away, looking at how ill-defined Bonnie looks.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting RedStickCasterette:


Well, I've watched/read him or her for five years on here. Just seemed so sincere this time with Bonnie, lol. Never gives any data or proof, though.

I do wonder if "it" is more that one person.


The thing that gets me most is the "YOU ARE WRONG, I HAVE INFORMATION IN FRONT OF ME THAT PROVES MY CASE" posts...yet no information is ever given LOL!
Member Since: September 24, 2005 Posts: 33 Comments: 9265
1969. IKE
Quoting tkeith:


New Orleans, Louisiana (Airport)
Updated: 24 min 50 sec ago
83 °F
Overcast
Humidity: 79%
Dew Point: 76 °F
Wind: Calm

Pressure: 30.01 in (Rising)
Heat Index: 91 °F

I'm serious...lol




Mobile, Alabama (Airport)
Updated: 24 min 58 sec ago
Mostly Cloudy
80 °F
Mostly Cloudy
Humidity: 94%
Dew Point: 78 °F
Wind: Calm
Pressure: 30.02 in (Steady)
Heat Index: 86 °F
Visibility: 6.0 miles
UV: 0 out of 16
Pollen: 3.10 out of 12
Pollen Forecast new!
Clouds:
Mostly Cloudy 20000 ft
(Above Ground Level)
Elevation: 217 ft


Gulfport, Mississippi (Airport)
Updated: 29 min 17 sec ago
Mostly Cloudy
84 °F
Mostly Cloudy
Humidity: 76%
Dew Point: 76 °F
Wind: 5 mph from the NNW
Pressure: 30.00 in (Steady)
Heat Index: 93 °F
Visibility: 10.0 miles
UV: 0 out of 16
Pollen: 2.50 out of 12
Pollen Forecast new!
Clouds:
Scattered Clouds 7000 ft
Mostly Cloudy 10000 ft
(Above Ground Level)
Elevation: 26 ft
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting atmosweather:


Standard operating procedure for him.


Well, I've watched/read him or her for five years on here. Just seemed so sincere this time with Bonnie, lol. Never gives any data or proof, though.

I do wonder if "it" is more that one person.
Member Since: Posts: Comments:
1967. tkeith


New Orleans, Louisiana (Airport)
Updated: 24 min 50 sec ago
83 °F
Overcast
Humidity: 79%
Dew Point: 76 °F
Wind: Calm

Pressure: 30.01 in (Rising)
Heat Index: 91 °F

I'm serious...lol

Member Since: November 1, 2004 Posts: 25 Comments: 8912
Quoting RedStickCasterette:


I don't get it either. I read/watched him say she was RIP and them boom, she was going to come back. I was like, "psycho much?" Wondered if he saw something no one else saw, lol.


Standard operating procedure for him.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting IKE:


Yeah....lol!




*spits out coffee on keyboard, laughing*




I don't understand stormtop. A few days ago he said no development in July....2 days ago he was killing Bonnie off....last night he's propping it up......

Enough said....



I don't get it either. I read/watched him say she was RIP and them boom, she was going to come back. I was like, "psycho much?" Wondered if he saw something no one else saw, lol.
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I was hoping for a good breeze...

Bonnie was nice to watch and learn from, though.
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1963. IKE
Quoting RedStickCasterette:


LOL did you save that quote? LOL.


Yeah....lol!


Quoting tkeith:
Hmmm...RI?

*rolls eyes*

there is not even a breeze here Ike...


*spits out coffee on keyboard, laughing*


Quoting atmosweather:


LOL I had sprite through my nose on a couple of those "visits" earlier.


I don't understand stormtop. A few days ago he said no development in July....2 days ago he was killing Bonnie off....last night he's propping it up......

Enough said....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
1962. tkeith
well, we got a nice practice run yesterday securing our cranes and equipment...I'm sure we'll see the real thing before the seasons over...
Member Since: November 1, 2004 Posts: 25 Comments: 8912
I need a trained monkey to click "refresh" so
my finger doesn't get worn out,lol..(Sorry,PETA)
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.