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 reedzone:
I've never seen a La Nina that was below 10 storms...


I believe what you are saying. I just wanted to hear it from you!
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What is going on with all the ULL. I dont remember a time when there seemed to be so many in the tropics interacting with each other. Is it the time of year (before CV starts)?


Or is this a greater scale type of event happening.... Like Dr. Masters said in one of his global warming blogs. Yes the earth may be heating up and that would mean higher temps all around the world and in the oceans.... BUT this will create more sheer and (i dont remember if he said this) maybe more SAL?


OH and Good morning... (pistons are firing today sorry in advance)
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Every one enjoy your day today i am going snorkling at caye caulker
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Quoting IKE:
It won't wind up below average in 2010. But I will admit, I was expecting more to this point. I'm not complaining though. Sunny weekends are nicer.

Gotta mow my front yard...L8R.......


You prediction of 13 named storms is a good one, especially since we haven't seen much yet. Hold on to it.
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Quoting BahaHurican:
But why above average?

I knew I should have cut and pasted StormW's synopsis from yesterday's blog...


Ugh, never mind. I was asking REED his thoughts, not Storms's.

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2153. IKE
It won't wind up below average in 2010. But I will admit, I was expecting more to this point. I'm not complaining though. Sunny weekends are nicer.

Gotta mow my front yard...L8R.......
Member Since: June 9, 2005 Posts: 23 Comments: 37858
2001, Barry formed in August as well.. They had 15 storms, a La Nina year as well

1 Tropical Storm ALLISON 5-19 JUN 50 1000 -
2 Tropical Storm BARRY 2- 8 AUG 60 990 -
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2151. IKE
Mike Seidel..."I think it's time to cue up the fat lady."

RIP Bonnie. It's over.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
I've never seen a La Nina that was below 10 storms...
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We are actually above average compared to 1998, Bonnie formed in August that year..

1 Tropical Storm ALEX 27 JUL- 2 AUG 45 1002 -
2 Hurricane BONNIE 19-31 AUG 100 954 3
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But why above average?

I knew I should have cut and pasted StormW's synopsis from yesterday's blog...
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Quoting IKE:
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT SAT JUL 24 2010

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
DEPRESSION BONNIE LOCATED ABOUT 215 MILES EAST-SOUTHEAST OF THE
MOUTH OF THE MISSISSIPPI RIVER.

A LARGE BUT DISORGANIZED AREA OF SHOWERS AND THUNDERSTORMS LOCATED
OVER THE CENTRAL CARIBBEAN IS ASSOCIATED WITH A TROPICAL WAVE
INTERACTING WITH AN UPPER-LEVEL LOW. DEVELOPMENT OF THE SYSTEM IS
NOT ANTICIPATED...AND THERE IS A LOW CHANCE...NEAR ZERO...OF THIS
SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER ROBERTS/AVILA



Near 0%???

Ha here we go, lol.

Waiting...
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2145. tkeith
THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
DEPRESSION BONNIE LOCATED ABOUT 215 MILES EAST-SOUTHEAST OF THE
MOUTH OF THE MISSISSIPPI RIVER.

Landfall in 11.9hrs :)
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Quoting RedStickCasterette:


How so you know things will ramp up?


Look how Alex evolved? Became a category 2 storm with a pressure of a category 3-4 storm. Pressures are lower then normal in the Atlantic, plus there is alot of heat. The High pressure is setting up to be a player in the long term, once the Cape Verde systems get going, and they will as usual with every Hurricane Season. Wind shear should start to decrease as La-Nina gets stronger and also, with La-Ninas, I don't think there ever was a season with a below average of named storms. We will definitely get over 10 storms. I'm thinking about maybe one more this month, 5 in August, 7 in September, 3 in October, and maybe 1-2 in November and can't rule out a December storm. La-Ninas tend to give us late storms.
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Quoting DestinJeff:
Bob Barker-casting for Bonnie:



LOL
Member Since: July 7, 2010 Posts: 0 Comments: 5682
2141. IKE
Quoting DestinJeff:
Bob Barker-casting for Bonnie:




Bumbling Bonnie.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting reedzone:
We had Alex and Bonnie.. We aren't really below average, 2009 ythis time had nothing.


Exactly but why above average?

Forget all they hype and casting.

If its below, then we are bored not having anything to follow, if its above, well, some of us may have trouble.

I hope for the best...period.
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2137. IKE
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT SAT JUL 24 2010

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
DEPRESSION BONNIE LOCATED ABOUT 215 MILES EAST-SOUTHEAST OF THE
MOUTH OF THE MISSISSIPPI RIVER.

A LARGE BUT DISORGANIZED AREA OF SHOWERS AND THUNDERSTORMS LOCATED
OVER THE CENTRAL CARIBBEAN IS ASSOCIATED WITH A TROPICAL WAVE
INTERACTING WITH AN UPPER-LEVEL LOW. DEVELOPMENT OF THE SYSTEM IS
NOT ANTICIPATED...AND THERE IS A LOW CHANCE...NEAR ZERO...OF THIS
SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER ROBERTS/AVILA

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting reedzone:
We had Alex and Bonnie.. We aren't really below average, 2009 at this time had nothing.

Neither did 2004.
Member Since: July 7, 2010 Posts: 0 Comments: 5682
Quoting BahaHurican:
Morning everybody.

He still keeps his own blog going also. Took a peep in there the other day. Had some halfway decent wx graphics.

Hi Baha.
Member Since: July 7, 2010 Posts: 0 Comments: 5682
2134. tkeith
Quoting DestinJeff:
I think we'll see around 15 storms by September 2011.
I'd agree with ya Jeff...but my "guesscasting" skills just aint what they used to be...
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We had Alex and Bonnie.. We aren't really below average, 2009 at this time had nothing.
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Quoting reedzone:
Just wait, things will ramp up, conditions are ripe for a active season. Still holding on to 15-18 named systems by December.


How so you know things will ramp up?
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Morning everybody.

Quoting tkeith:
CycloneBuster...he's still around. I dont think he posts in Doc's blog anymore, but I've seen him on other blogs here.
He still keeps his own blog going also. Took a peep in there the other day. Had some halfway decent wx graphics.
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2128. IKE
Quoting Hardcoreweather2010:


Now that you said that I am sure that we will have 99L before the end of the day :)


LOL...probably.

Bonnie(:
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting tkeith:
Take your leaf blower...


leaf blower
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Quoting IKE:


Last week of July looks like it will be...little to nothing in the Atlantic.


I hope so, as far as land-falling.
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Quoting IKE:


Last week of July looks like it will be...little to nothing in the Atlantic.


Now that you said that I am sure that we will have 99L before the end of the day :)
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Just wait, things will ramp up, conditions are ripe for a active season. Still holding on to 15-18 named systems by December.
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2123. IKE
Quoting RedStickCasterette:


So what you mean, Ike?


Last week of July looks like it will be...little to nothing in the Atlantic.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:
If.... was about all there was with Bonnie. That should take care of July in the Atlantic basin. May see another invest, but nothing significant.

The excuse, it's early in the season....won't apply much longer.


Sorry Ike, but this is still going to be an active season. Remember 2004? started in early August.
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Quoting IKE:
If.... was about all there was with Bonnie. That should take care of July in the Atlantic basin. May see another invest, but nothing significant.

The excuse, it's early in the season....won't apply much longer.


So what you mean, Ike?
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Quoting DestinJeff:
If 2010 had a sound effect, it would have to be this one:



LoL
Member Since: July 7, 2010 Posts: 0 Comments: 5682
2118. IKE
Quoting DestinJeff:
If 2010 had a sound effect, it would have to be this one:




LOL!
Member Since: June 9, 2005 Posts: 23 Comments: 37858
2117. IKE
If.... was about all there was with Bonnie. That should take care of July in the Atlantic basin. May see another invest, but nothing significant.

The excuse, it's early in the season....won't apply much longer.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Member Since: Posts: Comments:
2114. tkeith
Quoting Asta:

Hope is not an effective plan.


New Orleans, Louisiana (Airport)
Updated: 15 min 55 sec ago
84 °F
Overcast
Humidity: 82%
Dew Point: 78 °F
Wind: 5 mph from the NNW

Pressure: 30.04 in (Rising)

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Quoting reedzone:
If Bonnie would have stayed on the southern solution, we would still have a Tropical STorm, the CIMMS shear map explains it all. 10-20 knots south of where Bonnie is now. She went too far north.


Well good thing she did.

Although a nice breeze would have been nice...
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If Bonnie would have stayed on the southern solution, we would still have a Tropical STorm, the CIMMS shear map explains it all. 10-20 knots south of where Bonnie is now. She went too far north.
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2111. KEEPEROFTHEGATE (Mod)
Quoting IKE:


I've seen that exact statement about 1,000 times this season.


LMAO...Mike Seidel....no wind at Dauphin Island,AL.!!!!!!!!! Sea oats dead still.
well if ya put some fans on the beach he could stand in front of them to make it look that way then we need a garden hose to spray him down to look like rain the fan will give it that driving rain look then you need a moonshine jug to blow in to give it that howling wind sound come on they can do this its easy
Member Since: July 15, 2006 Posts: 171 Comments: 53835

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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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