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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111. xcool
lmao
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Not much happening... yet... hmmm where are all of the NOLA panic casters?

we're out puttin our shutters up...between beers.
Member Since: November 1, 2004 Posts: 25 Comments: 8926
Next!!
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Quoting angiest:


That must be what CMC and ECMWF have been trying to show for awhile.
Yes they mentioned ECMWF.
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Not much happening... yet... hmmm where are all of the NOLA panic casters?



AOI

AOI

AOI

AOI

Landfall Points

TS BUSTED FORECAST ALIBI
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Quoting Levi32:
UKMET and JMA see the MJO running back to mommy in the Atlantic. That makes more sense given the global heat pattern than the MJO running wild in the parts of the world where there is no surplus of heat.




LOL... "Running back to mommy"
Member Since: July 7, 2010 Posts: 0 Comments: 5684
Quoting Levi32:
ECMWF didn't do that badly on Bonnie. She was a glorified tropical wave with a very small, closed circulation with westerlies only extending a few miles south of the center. The ECMWF showed it as a highly amplified tropical wave that arguably could have developed into a weak tropical cyclone for a while and that is what has happened.


That's what I was thinking too. :)
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91. FLdewey 4:23 PM CDT on July 23, 2010

where's your tie dude?
Member Since: November 1, 2004 Posts: 25 Comments: 8926
Quoting Levi32:
UKMET and JMA see the MJO running back to mommy in the Atlantic. That makes more sense given the global heat pattern than the MJO running wild in the parts of the world where there is no surplus of heat.



this may cause a big drop in numbers if it lasts till 3rd week of august we wait and see
Member Since: July 15, 2006 Posts: 171 Comments: 53841
102. xcool
now we go back watch wave..
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TropicalDepression Bonnie was^heading for a NewOrleans landfall in ~27hours.
(Straightline^projection using its last 2 positions. Take with HUGE grain of salt)
Copy&paste 24.7N79.8W, 25.4N80.3W, 25.8N81.1W-26.2N81.9W, 26.2N81.9W-29.7N89.6W, BIX, 22.3N74.0W, 18.5N87W, TAM, 28.7N88.4W into the GreatCircleMapper
Shortest red line denotes the movement between last two positions. Below the map shows:
TD.Bonnie had a heading of 299.1degrees (6.6degrees north of WestNorthWest) while traveling
a distance of 57miles(~92kilometres) over 3hours at a speed of 19mph(~31k/h), and was
529miles(~852kilometres) away from the coast in the direction of its heading.

^ Straightline projections are not forecasts of what will happen in the future,
especially not for TropicalCyclones. They aftcast what has already happened.
* DeepwaterHorizon is marked at 28.7N88.4W
Member Since: August 21, 2007 Posts: 0 Comments: 4860
Quoting KEEPEROFTHEGATE:
be gone all afternoon just got in from work


Good luck... it looks like its going to be a crazy afternoon :)
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Was out for a while. Has anything happened?
Example: Organization, New Coordinates, Dissipation, Etc.
Member Since: July 7, 2010 Posts: 0 Comments: 5684
Quoting Patrap:
...Cant ya hear my heart beat,,itsa Love Beat,..
Wow!! First time I've ever seen the Defranco family quoted on a blog!!!
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Quoting FLdewey:


What a turd in the punch bowl.

We have to endure the baseless, adolescent and totally ludicrous predictions over, and over, and over, and over again... so now a little fun is fair play. I would say quit whining, but I understand that's your thing.


Wow! Not THAT is mature and responsible. I love this blog!!!
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UKMET and JMA see the MJO running back to mommy in the Atlantic. That makes more sense given the global heat pattern than the MJO running wild in the parts of the world where there is no surplus of heat.



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Quoting IKE:
Found this from this mornings San Juan discussion and I got hammered on here the other day for posting the MJO maps...

"ASIDE FROM TS BONNIE NEAR THE BAHAMAS...TROP ATLC VERY QUIET AND
MJO PROGNOSIS CONTINUE TO SUGGEST A STRONG DOWNWARD PHASE ACROSS
THE WRN HEMISPHERE OVR THE NEXT TWO WEEKS POSSIBLY LASTING
THROUGH THE THIRD WEEK OF AUGUST AS MJO SIGNAL CONTINUES TO
PROPAGATE INTO THE MARITIME CONTINENT/WRN PACIFIC."



Completely based on the GFS operational though, which I find to be pretty ridiculous. It's the outlier compared to the other model forecasts for the MJO right now. We should see a week or so of weak downward motion but the MJO shouldn't really get out of octant 3 or 4 before curving right back into the Atlantic by the 2nd week of August.



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Quoting angiest:


CMC barely has it now and ECMWF doesn't seem to pick it up at all anymore.


Ah ok. Thanks. Could pick it up again. This model is showing a pretty strong system coming out of the Caribbean. Looks like from a wave approaching from the east. But as always wait and see. :)

Link
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be gone all afternoon just got in from work
Member Since: July 15, 2006 Posts: 171 Comments: 53841
Quoting Levi32:
As long as the surface circulation is closed this is still a tropical cyclone, but may not remain one all the way to the north gulf coast. Either way, whether it's an open wave or not, weather effects will be the same. Some rain squalls and that's it. This is a ragged system as expected and will all but die in the gulf. Strengthening isn't likely.


Just looked at a few stations just south of Naples and there was a wind shift on a couple of them from the NW around an hour ago to the E now. The LLC is extremely ill-defined but it appears as if it is somehow still closed. I'd say it won't be for much longer unless conditions drastically change.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
it is what it is
got lucky this time
now we wait till next time
Member Since: July 15, 2006 Posts: 171 Comments: 53841
87. IKE
Quoting KEEPEROFTHEGATE:
03L/OW/XX
FINAL MARK
26.3N/81.3W


LOL..."final mark".
Member Since: June 9, 2005 Posts: 23 Comments: 37858
85. IKE
Found this from this mornings San Juan discussion and I got hammered on here the other day for posting the MJO maps...

"ASIDE FROM TS BONNIE NEAR THE BAHAMAS...TROP ATLC VERY QUIET AND
MJO PROGNOSIS CONTINUE TO SUGGEST A STRONG DOWNWARD PHASE ACROSS
THE WRN HEMISPHERE OVR THE NEXT TWO WEEKS POSSIBLY LASTING
THROUGH THE THIRD WEEK OF AUGUST AS MJO SIGNAL CONTINUES TO
PROPAGATE INTO THE MARITIME CONTINENT/WRN PACIFIC."

Member Since: June 9, 2005 Posts: 23 Comments: 37858
03L/OW/XX
FINAL MARK
26.3N/81.3W
Member Since: July 15, 2006 Posts: 171 Comments: 53841
Quoting sammywammybamy:


IKE,

Shall i Say RIP BONNIE.

Yes, say it, say it! LOL!
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ECMWF didn't do that badly on Bonnie. She was a glorified tropical wave with a very small, closed circulation with westerlies only extending a few miles south of the center. The ECMWF showed it as a highly amplified tropical wave that arguably could have developed into a weak tropical cyclone for a while and that is what has happened.
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oh wow
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As pathetic as the overreactions to some systems are, it is even more pathetic when people bait them and try to make fun of them if they are wrong

grow up people, its ok to be wrong, its not ok to throw other peoples' predictions in their faces
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Quoting Levi32:
As long as the surface circulation is closed this is still a tropical cyclone, but may not remain one all the way to the north gulf coast. Either way, whether it's an open wave or not, weather effects will be the same. Some rain squalls and that's it. This is a ragged system as expected and will all but die in the gulf. Strengthening isn't likely.
Agree and too much made of designation. But it will mean a little more if pressures drop and LLC reforms. Rain will only be issue if it slows down.
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Quoting homelesswanderer:
Sorry if its already been said/asked is that naked swirl moving west south of the convection Bonnie's coc?

Isnt that how she started out? Maybe we've come full circle with her. :)

exactly.
The shear is supposed to be a bit higher this time.
The center of circulation is there and thats the hard part.
So now see if the convection builds back while over water or if it shears off faster than it can build...
There is no way to know the answer to this at this point in time.
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Quoting homelesswanderer:


Yeah I've seen that too. Haven't looked at the recent runs though.


CMC barely has it now and ECMWF doesn't seem to pick it up at all anymore.
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Quoting IKE:
Fort Myers is within 25 miles of the new coordinates.....

Fort Myers, Florida (Airport)
Updated: 13 min 12 sec ago
Overcast
81 °F
Overcast
Humidity: 91%
Dew Point: 78 °F
Wind: 13 mph from the NE
Pressure: 29.89 in (Steady)

Heat Index: 89 °F
Visibility: 10.0 miles
UV: 2 out of 16
Pollen: 3.90 out of 12
Pollen Forecast new!
Clouds:
Few 800 ft
Mostly Cloudy 2500 ft
Overcast 3700 ft
(Above Ground Level)
Elevation: 16 ft


Nothing much at Sanibel either...
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Link
Herte's the Link I spoke of
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Calling all the folks who claimed Bon was going to be Cat 1-2...hello, anyone out there...hello, hello.

Cue the "Bonnie is going to blow up in the GOM" in 3...2....1
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69. IKE
Quoting Levi32:
As long as the surface circulation is closed this is still a tropical cyclone, but may not remain one all the way to the north gulf coast. Either way, whether it's an open wave or not, weather effects will be the same. Some rain squalls and that's it. This is a ragged system as expected and will die in the gulf. Strengthening isn't likely.


Raining here at my house now, inland Florida panhandle.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
yeah the season will be quiet for a while longer bonnie was a bust just rain and a breeze just like I called it.next!:)
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Looking at satellite it is a good possibility that the weak convection associated with Bonnie may just continue to drift towards the north as the naked LLC continues to move towards the WNW at its rapid rate. If this holds true, it could be a rainy night in the Florida panhandle. Bonnie should no longer be a tropical depression by 11 P.M unless it can organize by then, which at this point seems unlikely.

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Quoting angiest:


That must be what CMC and ECMWF have been trying to show for awhile.


Yeah I've seen that too. Haven't looked at the recent runs though.
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Quoting IKE:
This is a TD?




A very badly sheared TD
It still is an area of low pressure with a LLCC and it used to have convection..
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Quoting FLdewey:


My name is Dewey, not Buddy.

Yes I have been bracing myself against the half inch of rain I've received today. It's a miracle I'm still connected to the


OMG..!


We lost Kenny..

I mean Dewey
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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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