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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Quoting fallinstorms:


don't matter

the wind is too rough

and the sea is dry

they need more then heat

The sea is too dry, eh? Is the ice too hot? Is the air too heavy?
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i forgot how it goes....

dude (short) = c'mon
duuuuude (long) = what are you thinking
duuuudddde = party time
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Quoting atmoaggie:
Is it the averaging? Nothing close to the -3 mb anomaly in your 2010 plot.....

And, ehh, may be a decent connection. But, you well know that patterns *can* change as fast as 2 weeks. all it takes is a large fluctuation in the NAO and *poof*.


For the SW Atlantic and Gulf of Mexico -1.8mb is a pretty dang good 9-month average anomaly. What matters more is the shape and location of the below-normal pressures. It's entirely believable that 2010 could have lower pressures than the analog years....but the overall pattern is similar.

And I'll post this image again from the CPC, the typical positive NAO pattern in the summer is more of a tripole pattern that actually favors lower pressures over the tropics. The numerical index of the NAO is not a cut and dried indicator of the pattern in the Atlantic during the hurricane season. The pattern is much more flexible and the oscillation can take many forms.

Furthermore, I can't really see there being anything but lower than normal pressures in the tropical Atlantic with SSTs as warm as they are, can you? Pressures are already way above normal in the Pacific like they should be due to the cold water. That has to be balanced out in the Atlantic and Indian Oceans where the water is warm.

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306. IKE
Quoting Patrap:
Ike ..I best get my Garage Sale stuff in..,

But now the Work day folks in da hood are showing up with dollars and py-rooting thru da clothes.

Decisions,decisions..


LOL...the hood.

...............................................


Here's the eastern Atlantic view on the latest ECMWF through Aug. 2nd....Link
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T-Storms moving, looks like a wet one tomorrow.

Mobile Radar
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I don't understand the thought process of all the posters claiming this season is some sort of bust, but I also don't understand why they continue to garner responses from our more knowledgeable and responsible contributors. Give these attention hounds a big fat -, or report them in extreme circumstances, then simply ignore them. My list is 200 strong and growing. In fact, the ability to ignore nuisance posters is the only real reason I set up an account... I think you will find that this method provides for a more sane and enjoyable WU experience, and drastically reduces the xanax and thorazine budget.
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Quoting homelesswanderer:


Makes sense to me (and not a lot does) LOL. If I can understand anyone can. And I believe the poofers do too. But they have no patience. And don't realize that sometimes you have to wait to get what you want. If ya want an active season just wait you'll get it.


Perfectly stated.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting atmoaggie:
And because it is for Californians, it isn't usually friendly...
(yeah, kidding again, somewhat)


LOL!
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Quoting EtexJC:


Listen buddy, we call people from cal-e-for-ni-ans dudes...
And because it is for Californians, it isn't usually friendly...
(yeah, kidding again, somewhat)
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Quoting TexasHurricane:


Thanks storm ......here comes August,September and October.
I have to agree TH. Late May gave us some strong tropical waves, June a bit of a lull, July we had Alex, almost Bonnie south of La., Bonnie, almost Collin in the BOC. Warnings, shots across the bow. Get yourselves ready for whats to come. We have been warned.
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Quoting FLdewey:
<--- connected via Sat Phone



Well in my eyes when you call someone "buddy" or "dude" it's not usually "being nice". I will give you the benefit of the doubt.

I do give you credit however... it HAS been like 4 hours since you congratulated yourself.

Kudos!


Listen buddy, we call people from cal-e-for-ni-ans dudes...
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297. xcool
AUG 10 NEXT NAMED storm imo
Member Since: September 26, 2009 Posts: 2 Comments: 15649
Quoting CaptDanny:

Dude Chill

What'd ya think the snow's for? ;)
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Quoting Tazmanian:



Bonnie
Oh, right, Bonnie. Forgot about the former wet-spot. (j/k)
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Ike ..I best get my Garage Sale stuff in..,

But now the Work day folks in da hood are showing up with dollars and py-rooting thru da clothes.

Decisions,decisions..
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Quoting Levi32:


Would have to disagree there, at least with what I am seeing.

Let's look at some of our top analog years, 1964, 1998, and 2005:

July MSLP Anomalies for 1964, 1998, and 2005:



Now look at the heart of the hurricane season:

August-September-October MSLP Anomalies for 1964, 1998, and 2005:



Is it the averaging? Nothing close to the -3 mb anomaly in your 2010 plot.....

And, ehh, may be a decent connection. But, you well know that patterns *can* change as fast as 2 weeks. all it takes is a large fluctuation in the NAO and *poof*.
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290. IKE
Quoting IKE:


I didn't see any through Aug. 2nd.


Here's the run...12Z ECMWF...
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Quoting Tazmanian:
am forcasting a foot of snow for FL

Dude Chill
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Quoting homelesswanderer:


Makes sense to me (and not a lot does) LOL. If I can understand anyone can. And I believe the poofers do too. But they have no patience. And don't realize that sometimes you have to wait to get what you want. If ya want an active season just wait you'll get it.


so true... :)
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Quoting atmoaggie:
Who?



Bonnie
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Quoting seflagamma:
yes, as Pat would say...
You have been "Mommed" LOL


Lolol.
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am forcasting a foot of snow for FL
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283. IKE
Quoting atmoaggie:

Hey, look. It's an ULL. And a mid-lev trof.



Bonnie and that ULL....never could get away from each other. A lot of experts were saying it probably would, but it never really did.
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Quoting Tazmanian:



and where is Bonnie
Who?
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Quoting StormW:
Ok...here's some facts, then I have to go for a bit.

2002, 2004, and 2009 were all El Nino years.

Storm total:
2002 = 12
2004 = 15
2009 = 09

2009 was pretty much ALL season plagued by wind shear, dry air, stronger A/B high, and cooler sst's. We had how many? Nine! In fact 9, 3, and 2 What's average? 10, 6, 2. Pretty close to an average year...wouldn't you say?

We are in a MODERATE LA NINA, RECORD SST's, SHEAR BELOW CLIMATOLOGY, and so on. BIG DEAL, we have had some some dust. If we can pull those kind of numbers out of El Nino years, with less than favorable conditions than we have now, we darn sure can pull more than an average season...well above average.

Those who wish, can now carry on with their fantasy of a poof season.


Makes sense to me (and not a lot does) LOL. If I can understand anyone can. And I believe the poofers do too. But they have no patience. And don't realize that sometimes you have to wait to get what you want. If ya want an active season just wait you'll get it.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
278. IKE
Quoting gbreezegirl:

We are getting a bad storm now in the panhandle (Gulf Breeze/pens bch)you getting any of this Ike??


Thundershowers all around.
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Announcer: We are gathered here today...to witness the cremation of a storm named Bonnie.
*Public sobs*
*ULL walks in, rips Bonnie apart*
Public and announcer: O_o
ULL: :P
EDIT:
*Spirit of Bonnie comes, slaps ULL in the face.*
Public: Yay!
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yes, as Pat would say...
You have been "Mommed" LOL
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Yes...it is getting quite active in the panhandle...
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Quoting atmoaggie:

Hey, look. It's an ULL. And a mid-lev trof.



and where is Bonnie
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Quoting StormW:
Ok...here's some facts, then I have to go for a bit.

2002, 2004, and 2009 were all El Nino years.

Storm total:
2002 = 12
2004 = 15
2009 = 09

2009 was pretty much ALL season plagued by wind shear, dry air, stronger A/B high, and cooler sst's. We had how many? Nine! In fact 9, 3, and 2 What's average? 10, 6, 2. Pretty close to an average year...wouldn't you say?

We are in a MODERATE LA NINA, RECORD SST's, SHEAR BELOW CLIMATOLOGY, and so on. BIG DEAL, we have had some some dust. If we can pull those kind of numbers out of El Nino years, with less than favorable conditions than we have now, we darn sure can pull more than an average season...well above average.

Those who wish, can now carry on with their fantasy of a poof season.


Thanks storm ......here comes August,September and October.
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#263, StormW, that just about says it all.
I agree with you, some people do not get it.


and most of those I have on ignore so I would not even see their silly comments if you folks would stop quoting their post! LOL

j/k.. you can do what you want...
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Hey, look. It's an ULL. And a mid-lev trof.

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Quoting StormW:
Ok...here's some facts, then I have to go for a bit.

2002, 2004, and 2009 were all El Nino years.

Storm total:
2002 = 12
2004 = 15
2009 = 09

2009 was pretty much ALL season plagued by wind shear, dry air, stronger A/B high, and cooler sst's. We had how many? Nine! In fact 9, 3, and 2 What's average? 10, 6, 2. Pretty close to an average year...wouldn't you say?

We are in a MODERATE LA NINA, RECORD SST's, SHEAR BELOW CLIMATOLOGY, and so on. BIG DEAL, we have had some some dust. If we can pull those kind of numbers out of El Nino years, with less than favorable conditions than we have now, we darn sure can pull more than an average season...well above average.

Those who wish, can now carry on with their fantasy of a poof season.

See My response StormW comment#253
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266. IKE
Quoting MiamiWarnings:
ike did the 3pm ecm show any threaters?


I didn't see any through Aug. 2nd.
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In Fort Lauderdale Beach the worst part of Bonnie came thru about 12:45-1:15 pm this afternoon with heavy winds out of the SE 25-35 mph gust hitting 40 mph. Several palm frowns were blown down but other than that just couple of squall lines came thru during the morning the last one came thru about 2pm.
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PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS Link
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS, MD
300 PM EDT FRI JULY 23 2010

6-10 DAY OUTLOOK FOR JUL 29 - AUG 02, 2010

TODAY'S ENSEMBLE MEAN SOLUTIONS SHOW GOOD AGREEMENT ON THE EXPECTED MEAN
500-HPA CIRCULATION PATTERN, FEATURING TROUGHS ALONG THE WEST COAST AND ACROSS
THE NORTHEAST CONUS, A SUBTROPICAL RIDGE CENTERED OVER THE SOUTHERN ROCKIES, A
POSITIVELY-TILTED TROUGH EXTENDING FROM NORTHEAST ALASKA TO SOUTHWEST ALASKA,
AND A RIDGE CENTERED OVER THE BERING SEA. RECENT ENSEMBLE FORECASTS SHOW A
WESTWARD RETROGRESSION OF THE PATTERN, SUPPORTED BY MODEL FORECASTS OF A LARGE
POSITIVE HEIGHT ANOMALY CENTERED OVER THE NORTHEAST ATLANTIC. THE ENSEMBLES
DISPLAY MINOR DIFFERENCES IN THE AMPLITUDE AND POSITION OF THE RESPECTIVE
TROUGHS ALONG BOTH COASTS OF NORTH AMERICA. TODAY'S MANUAL BLEND IS WEIGHTED
ENTIRELY ON THE ENSEMBLE MEAN SOLUTIONS, AS TODAY'S GFS AND ECMWF OPERATIONAL
MODEL SOLUTIONS ARE NOT IN AGREEMENT WITH THEIR RESPECTIVE ENSEMBLE MEANS.


A PATTERN SHIFT ASSOCIATED WITH THE MEAN TROUGH FAVORING NEAR TO BELOW-AVERAGE
TEMPERATURES IS FORECAST FOR THE NORTHEASTERN CONUS. THE COMBINATION OF WEAK
POSITIVE HEIGHT ANOMALIES ASSOCIATED WITH THE SUBTROPICAL RIDGE AND CONSISTENCY
FROM THE TOOLS SUPPORTS A FORECAST FOR ENHANCED PROBABILITIES FOR ABOVE-AVERAGE
TEMPERATURES FOR THE PLAINS, WESTERN GREAT LAKES AND SOUTHEASTERN STATES.
ENHANCED PROBABILITES FOR BELOW-AVERAGE TEMPERATURES ARE FORECAST ALONG THE
WEST COAST DUE TO THE EXPECTED TROUGH AND BELOW-AVERAGE SEA-SURFACE
TEMPERATURES.

So the pattern shift they speak of, The trough in the northeast Won't extend south enough to turn storms away if one threatened? Just trying to see the pattern shift. But maybe they mean something out west for all I know. :)
Member Since: August 15, 2008 Posts: 10 Comments: 3665
I think some are misunderstanding the word "hyperactive" season

If I remember right the "hyperactive" part is due to the ACE; meaning we will see well above the average in ACE for the season. We have a long way to go folks, those down-casting the season are mostly trolls looking to just get a rise out of people

Those who actually know about the tropics are fully aware that we have a long way to go in this season and many many storms still to track.
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Quoting Tazmanian:
the HH is up


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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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