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 atmosweather:


"Well I believe you may get your headlines, Mr. Ismay"


Call me Bruce, really. :)
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Quoting ACEhigh:
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.


Good post!

I fell into that trap myself yesterday, responding to idiots that were clearly just trying to rile me up.

I probably even ended up on some ignore lists myself.

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Quoting WeatherNerdPR:

Interesting week ahead?
It's always an interesting week during hurricane season.
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Quoting Twinkster:
18Z GFS shows cape verde hurricane situated north of puerto rico on august 8th. Begins developing the system about a week from now by the cape verde islands

http://www.nco.ncep.noaa.gov/pmb/nwpara/analysis/carib/gfs/18/index_ten_l_loop.shtml


Lol. Nevermind my statement about the GFS.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Quoting ACEhigh:
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.


Most are just trying get under your skin by going against this season's thinking. I still expect an above average season but not 20 storms or more.
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Quoting KEEPEROFTHEGATE:
The formation of tropical cyclones is the topic of extensive ongoing research and is still not fully understood.

+1 KOTG , I still think climatology, upper atmospheric conditions and SST rules the roost in terms of predicting and forcasting cyclones or developing ones, yet there is plenty that is unknown. It's Nature's secret!
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Quoting homelesswanderer:


:) Thanks. The old caveat about getting what you wish for hardly needs to be said.


"Well I believe you may get your headlines, Mr. Ismay"
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting MiamiHurricanes09:
Here's the tropical wave about to emerge on satellite imagery.



We defiantly needs to watch this wave over the next couple of days. I'm too lazy to check but are any other models predicting development? We Also need to watch the area around Bermuda as Levi mentioned earlier.
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Quoting MiamiHurricanes09:
Here's the tropical wave about to emerge on satellite imagery.


Interesting week ahead?
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18Z GFS shows cape verde hurricane situated north of puerto rico on august 8th. Begins developing the system about a week from now by the cape verde islands

http://www.nco.ncep.noaa.gov/pmb/nwpara/analysis/carib/gfs/18/index_ten_l_loop.shtml
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Quoting CybrTeddy:


It was noted on a previous blog that the ECMWF has trouble picking up smaller storms due to lower resolution, this appears to be a smaller system so it could be stronger than what the ECMWF is indicating but the track and formation is completely probable and needs to be watched as this wave tracks over the Atlantic.


Thanks. Was wondering why it didn't see Bonnie and yet it looks like they had the end of the track and strength correct. Cmc didnt do bad either. Except of course over doing the strength. The gfs never seems to see anything this season.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Were just finishing the salad climatologically for a Given season. The Entree's are on the Grill and frying as well.
Best do a tad bit o work before ya go against Logic and well..dis information.

Its more than
a serie's of tubes,

..really.



Honest.

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Quoting WeatherNerdPR:

I wanna see the wave at 144hrs develop. Sounds interesting.


Well anything tropical 6 days out on a questionable model..( which all models are questionable pre-cyclonegenisis) would be an amazing revolution in technology. This is very speculative at best.
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Quoting MiamiHurricanes09:
The wave east of the Antilles can be tracked all the way back to 24 hours as it is seen that it is emerging off of the coast of Africa.

Here's the tropical wave about to emerge on satellite imagery.

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Quoting MiamiHurricanes09:
The wave east of the Antilles can be tracked all the way back to 24 hours as it is seen that it is emerging off of the coast of Africa.



Not a bad looking wave either..
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Quoting MiamiHurricanes09:
12z ECMWF takes the trough over Hispa�iola on a track very similar to Bonnie, with the exception that the trough ends up by Texas. It also shows a tropical wave accompanied by an area of low pressure just east of the Antilles by 144 hours. This wave ends up over Cuba by 240 hours.
The wave east of the Antilles can be tracked all the way back to 24 hours as it is seen that it is emerging off of the coast of Africa.

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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.
This is an excellent summary which should be archived and posted every time we have a spurious poofer.

You know, I wouldn't mind these poofers if they would at least base their reasoning on SOMEthing. Draw my attention to ONE factor supporting a slow season. But the only thing one can hear is "we haven't had any storms yet". That's like saying the Mets are going to win because the Yankees haven't scored yet - and it's the top of the first inning!
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New EUROSIP July forecasts for August-September-October still look bad for the Caribbean and United States. The forecast hasn't changed for months and it is verifying before our very eyes. The storms will come from this pattern. It is almost unavoidable.

Sea-level Pressure:



Precipitation:



2m Temperature:

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Quoting MiamiHurricanes09:

I'm not sure if I need to watch the area to the north of Hispaniola or the area to the south.
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Quoting Twinkster:


link
ECMWF images
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Quoting Levi32:
30-day MSLP anomalies worldwide:

Where are you gonna go for focusing of heat in the tropics, upward motion, and resulting tropical cyclones? The Atlantic, naturally.

Okay. If that remains as is, what TCs form will favor the Atlantic. But, would you say we see an uptick in total ACE worldwide, or remaining low?



Given the more hostile conditions that simply exist in the Atlantic (land, dust, shear, etc.), relative to the Super typhoon-generating West Pac, my leaning is to stay on a generally low total ACE. Does that really equate to a 20 named storm season, or close? I don't think so.

For this season to jump to the Northern Hemisphere ACE values of '98, '05, etc. (lower dots) would be quite a leap from recent or current levels. Almost appears to be something at play we aren't considering. At no time in the last 30 years, according to that plot, has N Hemisphere ACE jump from the values it is now to those of the analogue years (at least the ones from the last 30 years), though '91 would be the steepest. Time will tell.
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Quoting MiamiHurricanes09:
12z ECMWF takes the trough over Hispa�iola on a track very similar to Bonnie, with the exception that the trough ends up by Texas. It also shows a tropical wave accompanied by an area of low pressure just east of the Antilles by 144 hours. This wave ends up over Cuba by 240 hours.


The 12z NOGAPS tries to spin up something in the south Caribbean and bring it north like the FIMZ I posted does.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Quoting MiamiHurricanes09:
12z ECMWF takes the trough over Hispa�iola on a track very similar to Bonnie, with the exception that the trough ends up by Texas. It also shows a tropical wave accompanied by an area of low pressure just east of the Antilles by 144 hours. This wave ends up over Cuba by 240 hours.


link
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Quoting MiamiHurricanes09:
12z ECMWF takes the trough over Hispañiola on a track very similar to Bonnie, with the exception that the wave ends up by Texas. It also shows a tropical wave accompanied by an area of low pressure just east of the Antilles by 144 hours. This wave ends up over Cuba by 240 hours.

I wanna see the wave at 144hrs develop. Sounds interesting.
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Quoting MiamiHurricanes09:
12z ECMWF takes the trough over Hispañiola on a track very similar to Bonnie, with the exception that the wave ends up by Texas. It also shows a tropical wave accompanied by an area of low pressure just east of the Antilles by 144 hours. This wave ends up over Cuba by 240 hours.


It was noted on a previous blog that the ECMWF has trouble picking up smaller storms due to lower resolution, this appears to be a smaller system so it could be stronger than what the ECMWF is indicating but the track and formation is completely probable and needs to be watched as this wave tracks over the Atlantic.
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335. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15625
The formation of tropical cyclones is the topic of extensive ongoing research and is still not fully understood.
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Last attempt sorry
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12z ECMWF takes the trough over Hispaiola on a track very similar to Bonnie, with the exception that the trough ends up by Texas. It also shows a tropical wave accompanied by an area of low pressure just east of the Antilles by 144 hours. This wave ends up over Cuba by 240 hours.
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Quoting MiamiHurricanes09:
The ECMWF just updated their El Niño 3.4 forecast, now calling from us to enter a pretty strong La Niña, reaching almost -2.0˚C.




wow that could give CA a vary cold winter
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329. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15625
Quoting Levi32:


The sea is dry? Now I've heard everything lol.


Trade winds still below normal:



Well a dry sea would be pretty harsh on a Hurricane..

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http://www.ssd.noaa.gov/goes/east/carb/rb-l.jpg
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Quoting atmosweather:


Perfectly stated.


:) Thanks. The old caveat about getting what you wish for hardly needs to be said.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Quoting BahaHurican:
Afternoon all.

Amazing to see pple can fight over calling somebody "bud" or "dude".... lol amazing....

Glad to see there is at least some potential for Bonnie to arrive at the LA coast as... well... nothing. Hope that works out.

Meanwhile, wx here is fantastic - bright sun, light breeze, and just the best of summer...

Back later.


wtf, dude! (that's welcome to fridays, dude)
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May be Fox will have the Caribbean part of there forecast right: or there are 2 possibilities one right one wrong.http://www.ssd.noaa.gov/goes/east/carb/rb-l.jpg
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Link Storm W I'm busy doing pay day for the staff but could you brief me what the models have on this our what your thoughts are . Earlier i thought it might be shear induced but the shear has dropped 10 knots over the system today . Thanks in advance
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Quoting HouGalv08:
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.


Yep. Texas has had the most landfalls in September. The day with the most upper coast landfalls is September 13. Humberto and Ike classic case. Most upper TX coast major hurricane landfalls occur within one year of an El Nino year.
Ummmmm. Not that I study all this stuff. Its not like I have no life outside the tropics. Ok, I probably don't Lol. ;)
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Afternoon all.

Amazing to see pple can fight over calling somebody "bud" or "dude".... lol amazing....

Glad to see there is at least some potential for Bonnie to arrive at the LA coast as... well... nothing. Hope that works out.

Meanwhile, wx here is fantastic - bright sun, light breeze, and just the best of summer...

Back later.
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30-day MSLP anomalies worldwide (top image):

Where are you gonna go for focusing of heat in a tropical basin, upward motion, and resulting tropical cyclones? The Atlantic, naturally.

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Quoting EtexJC:
i forgot how it goes....

dude (short) = c'mon
duuuuude (long) = what are you thinking
duuuudddde = party time


rofl...true native Texans perfectally understand "dude!" ^u^
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Quoting MiamiHurricanes09:
The sea is too dry, eh? Is the ice too hot? Is the air too heavy?

LOL
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The ECMWF just updated their El Niño 3.4 forecast, now calling from us to enter a pretty strong La Niña, reaching almost -2.0˚C.

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what with the the 2 waves that are right behind it..channel 7 is aready talking about it.one on sunday and then on tuesday..channel 10 says nothing about it :(
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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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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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