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 Hardcoreweather2010:
Not goi
Not going to do that cause I want to be able to sell TWC video footage like I have in the past :)


K. Just sounded funny...
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Quoting Hardcoreweather2010:
Should I run behind Mike for the next live shot and pretend like I can't stand up cause of the strong winds ? LOL


I'm almost begging ya to...LOL!
Member Since: September 24, 2005 Posts: 33 Comments: 9265
About 3hours late but...
TropicalDepression Bonnie was^heading for a Houma,Louisiana landfall in ~20hours.
(Straightline^projection using its last 2 positions. Take with HUGE grain of salt)
Copy&paste 26.4N82.5W, 26.4N83.4W, 26.7N84.4W-27.0N85.1W, 27.0N85.1W-29.2N90.6W, 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 295.7degrees (3.2degrees north of WestNorthWest) while traveling
a distance of 48miles(~77kilometres) over 3hours at a speed of 16mph(~26km/h),
and was 368miles(~1,381kilometres) away from the coast in the direction of its heading.

^ A straightline projection does not forecast of what will happen in the future,
See blog1555post1853 for further explanation of what it does and doesn't do.
* DeepwaterHorizon is marked at 28.7N88.4W
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Not goi
Quoting RedStickCasterette:


YES! Do that, lol. I'll put the channel on now, lol.

Not going to do that cause I want to be able to sell TWC video footage like I have in the past :)
Member Since: January 24, 2010 Posts: 0 Comments: 529
Quoting IKE:


Thanks....

...BONNIE COULD DEGENERATE INTO AN AREA OF LOW PRESSURE...WARNINGS WILL LIKELY BE DISCONTINUED LATER THIS MORNING...
7:00 AM CDT Sat Jul 24
Location: 27.6°N 86.1°W
Max sustained: 30 mph
Moving: WNW at 18 mph
Min pressure: 1013 mb


Bonnie is a degenerate.

Sigh...
Member Since: Posts: Comments:
2055. IKE
BULLETIN
TROPICAL DEPRESSION BONNIE INTERMEDIATE ADVISORY NUMBER 8A
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032010
700 AM CDT SAT JUL 24 2010

...BONNIE COULD DEGENERATE INTO AN AREA OF LOW PRESSURE...WARNINGS
WILL LIKELY BE DISCONTINUED LATER THIS MORNING...


SUMMARY OF 700 AM CDT...1200 UTC...INFORMATION
----------------------------------------------
LOCATION...27.6N 86.1W
ABOUT 215 MI...345 KM ESE OF THE MOUTH OF THE MISSISSIPPI RIVER
ABOUT 160 MI...260 KM SSW OF APALACHICOLA FLORIDA
MAXIMUM SUSTAINED WINDS...30 MPH...50 KM/HR
PRESENT MOVEMENT...WNW OR 295 DEGREES AT 18 MPH...32 KM/HR
MINIMUM CENTRAL PRESSURE...1013 MB...29.91 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

NONE

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* DESTIN FLORIDA TO MORGAN CITY LOUISIANA...INCLUDING LAKE
PONTCHARTRAIN

THE TROPICAL STORM WARNING WILL LIKELY BE DISCONTINUED LATER THIS
MORNING.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA INCLUDING POSSIBLE
INLAND WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED BY
YOUR LOCAL NATIONAL WEATHER SERVICE FORECAST OFFICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 700 AM CDT...1200 UTC...THE CENTER OF TROPICAL DEPRESSION BONNIE
WAS LOCATED NEAR LATITUDE 27.6 NORTH...LONGITUDE 86.1 WEST. THE
DEPRESSION IS MOVING TOWARD THE WEST-NORTHWEST NEAR 20 MPH...32
KM/HR. A GRADUAL DECREASE IN FORWARD SPEED IS EXPECTED TODAY WITH
LITTLE CHANGE IN THE DIRECTION OF MOTION. ON THIS TRACK...THE
CENTER OF BONNIE IS FORECAST TO APPROACH THE NORTHERN GULF COAST
TONIGHT.

SATELLITE IMAGES AND DATA FROM A RECONNAISSANCE PLANE INDICATE THAT
BONNIE HAS BECOME LESS ORGANIZED. MAXIMUM SUSTAINED WINDS HAVE
DECREASED TO ARE NEAR 30 MPH...50 KM/HR...WITH HIGHER GUSTS.
STRENGTHENING IS BECOMING LESS LIKELY.

THE LATEST MINIMUM CENTRAL PRESSURE REPORTED BY AN AIR FORCE
HURRICANE HUNTER AIRCRAFT IS 1013 MB...29.91 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM FORCE WINDS MAINLY IN SQUALLS COULD REACH
PORTIONS OF THE NORTHERN GULF COAST LATER TODAY.

RAINFALL...BONNIE IS EXPECTED TO PRODUCE TOTAL RAINFALL
ACCUMULATIONS OF 1 TO 2 INCHES OVER PORTIONS OF SOUTHERN
LOUISIANA...SOUTHERN ALABAMA...SOUTHERN MISSISSIPPI...AND THE FAR
WESTERN FLORIDA PANHANDLE...WITH POSSIBLE ISOLATED MAXIMUM AMOUNTS
OF 3 INCHES.

STORM SURGE...STORM SURGE WILL RAISE WATER LEVELS BY AS MUCH AS 1 TO
3 FEET ABOVE GROUND LEVEL ALONG THE IMMEDIATE COAST NEAR AND TO THE
RIGHT OF WHERE THE CENTER MAKES LANDFALL ON THE NORTHERN GULF
COAST.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...1000 AM CDT.

$$
FORECASTER AVILA/ROBERTS
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting atmosweather:
W winds everywhere!!! LOL...it's still by definition a tropical depression...somehow. Although if convection doesn't fire near the center soon (and the stuff right now doesn't count) then it's just a remnant low with a closed circulation.


I guess the advisory answered that question!...What a horrible excuse for a tropical depression LOL!
Member Since: September 24, 2005 Posts: 33 Comments: 9265
2053. tkeith
2048. IKE 6:37 AM CDT on July 24, 2010
End this NHC....can you do it?

They're holdin off incase of IWRC :)

Member Since: November 1, 2004 Posts: 25 Comments: 8937
2052. IKE
Quoting atmosweather:


Dauphin Island, AL. Zero movement of the plants in the sand.


Thanks....

...BONNIE COULD DEGENERATE INTO AN AREA OF LOW PRESSURE...WARNINGS WILL LIKELY BE DISCONTINUED LATER THIS MORNING...
7:00 AM CDT Sat Jul 24
Location: 27.6°N 86.1°W
Max sustained: 30 mph
Moving: WNW at 18 mph
Min pressure: 1013 mb
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting Hardcoreweather2010:
Should I run behind Mike for the next live shot and pretend like I can't stand up cause of the strong winds ? LOL


YES! Do that, lol. I'll put the channel on now, lol.
Member Since: Posts: Comments:
W winds everywhere!!! LOL...it's still by definition a tropical depression...somehow. Although if convection doesn't fire near the center soon (and the stuff right now doesn't count) then it's just a remnant low with a closed circulation.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Should I run behind Mike for the next live shot and pretend like I can't stand up cause of the strong winds ? LOL
Member Since: January 24, 2010 Posts: 0 Comments: 529
2048. IKE
End this NHC....can you do it?



Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting IKE:


He in New Orleans?


Dauphin Island, AL. Zero movement of the plants in the sand.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
TWC is talking right now about moving for the next live shot . I am going to head back up to Mobile for now and if Bonnie wakes up I will start streaming my chase cam. Have a great day
Member Since: January 24, 2010 Posts: 0 Comments: 529
2045. tkeith
Quoting IKE:


He in New Orleans?
If he is he can sleep in...
Member Since: November 1, 2004 Posts: 25 Comments: 8937
Quoting tkeith:
Almost as funny as Geraldo bending over halfway then getting attacked by a palm tree during Dennis!!!

I think the scene in Gustave where he was bracing himself against the wind for a report, and he made it look like 100mph winds. Then two guys walked past behind him casually drinkin a beer was as funny :)


Oh wow I missed that. Perhaps power was out by then. Saw him right before, crying that the levees may give out again.

Dennis for him was a classic. Even O'Reilly put it up on "ridiculous moments" or something similar.
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2043. tkeith
Quoting atmosweather:


Yes during non-working hours...as much as possible.
good
Member Since: November 1, 2004 Posts: 25 Comments: 8937
2042. IKE
Quoting atmosweather:


LMAO its literally calm where Seidel is!!!


He in New Orleans?
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting IKE:


Doesn't look like it.


Dedicated to Bonnie...Link


LMAO its literally calm where Seidel is!!!
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting IKE:


Doesn't look like it.


Dedicated to Bonnie...Link


LMAO! have not heard that in ages.
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Member Since: January 24, 2010 Posts: 0 Comments: 529
2037. tkeith
Almost as funny as Geraldo bending over halfway then getting attacked by a palm tree during Dennis!!!

I think the scene in Gustave where he was bracing himself against the wind for a report, and he made it look like 100mph winds. Then two guys walked past behind him casually drinkin a beer was as funny :)
Member Since: November 1, 2004 Posts: 25 Comments: 8937
Quoting DestinJeff:
One thing I know for sure:

I'll never trust a pile of ants to make an accurate weather forecast again!


Been looking for the ant hints, but explain why NO tree roaches or red wasps this year? The cold winter?

I know you were joking...
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2035. IKE
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.


Doesn't look like it.


Dedicated to Bonnie...Link
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting tkeith:
Atmos you gonna be around for most of the season?


I hope he/she is.
Member Since: Posts: Comments:
Good Morning fellow bloggers!

My guess is as long as the swirl is visible on the visible, they'll keep it as a depression.

The rigs have already been evacuated, and there is no up side to having people return yet, even with the tiniest of odds of Bonnie flaring up. It would make them appear foolish. They're in a lose-lose situation, and erring on the side of cautious is the correct call.
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Quoting tkeith:
Atmos you gonna be around for most of the season?


Yes during non-working hours...as much as possible.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting RedStickCasterette:


So where is TWC? lol. I saw them yesterday in S. Florida with nothing going on.

Almost as funny as Geraldo bending over halfway then getting attacked by a palm tree during Dennis!!!


Mike is down here on Dauphin Island, AL in between 2 cabins close to the west end
Member Since: January 24, 2010 Posts: 0 Comments: 529
2028. tkeith
Quoting atmosweather:
They found 3 kt W winds...that's what's left of Bonnie LOL

112100 2610N 08637W 9249 00814 0151 +215 +169 271001 003 013 001 00
112130 2610N 08635W 9251 00813 0151 +215 +171 299002 003 012 001 00
112200 2610N 08634W 9249 00814 0151 +215 +173 287002 002 010 002 00
Atmos you gonna be around for most of the season?
Member Since: November 1, 2004 Posts: 25 Comments: 8937
Quoting Hardcoreweather2010:
I just spoke with Mike Siedel from TWC and he can't believe they sent him down here to cover this


So where is TWC? lol. I saw them yesterday in S. Florida with nothing going on.

Almost as funny as Geraldo bending over halfway then getting attacked by a palm tree during Dennis!!!
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2026. tkeith
2023. DestinJeff 6:24 AM CDT on July 24, 2010

Noriega Point...JMHO :)
Member Since: November 1, 2004 Posts: 25 Comments: 8937
They found 3 kt W winds...that's what's left of Bonnie LOL

112100 2610N 08637W 9249 00814 0151 +215 +169 271001 003 013 001 00
112130 2610N 08635W 9251 00813 0151 +215 +171 299002 003 012 001 00
112200 2610N 08634W 9249 00814 0151 +215 +173 287002 002 010 002 00
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting atmosweather:


Bonnie will not even produce as much storm surge or wave action onto the N-ern Gulf Coast as Alex did.


Well that's good news.
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I just spoke with Mike Siedel from TWC and he can't believe they sent him down here to cover this
Member Since: January 24, 2010 Posts: 0 Comments: 529
2021. tkeith
Quoting RedStickCasterette:



Don't the tides have something to do with it too? Whether its high or low tide?
Yes, We've had many days during this spill fiasco with SSE winds 20-30 mph, and it stacks alot of water on the coast.
Member Since: November 1, 2004 Posts: 25 Comments: 8937
Quoting RedStickCasterette:


Do you think we will get that surge? I had read Alex put some surge/oil into LA. I hope not.


Bonnie will not even produce as much storm surge or wave action onto the N-ern Gulf Coast as Alex did.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
2019. breald
I see this morning that Bonnie has fallen apart and never gained strenght.

What is next on the watch list?
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Quoting tkeith:
you think this will create that much?

I agree, 2-4 ft would push alot into the marsh.

time for bouy check.



Don't the tides have something to do with it too? Whether its high or low tide?
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2017. tkeith
Asta look at P451 graphics, it look like the winds are all from the NNE...?
Member Since: November 1, 2004 Posts: 25 Comments: 8937
Quoting atmosweather:
Well it looks like the HH plane is heading back E-ward to sample the southern semicircle...if they don't find any W winds then it's pretty much a broad trough.


Thanks for all your help tonight/this morning.

So when do we get the info back? Not that it appears to matter at this point. Just curious...
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2015. tkeith
Quoting Asta:

Ehem. 2-4 feet of storm surge with oil can have a devestating impact on people living along the coast of SE LA and MS.
you think this will create that much?

I agree, 2-4 ft would push alot into the marsh.

time for bouy check.
Member Since: November 1, 2004 Posts: 25 Comments: 8937
Quoting Asta:

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.


Do you think we will get that surge? I had read Alex put some surge/oil into LA. I hope not.
Member Since: Posts: Comments:
Well it looks like the HH plane is heading back E-ward to sample the southern semicircle...if they don't find any W winds then it's pretty much a broad trough.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
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.


So no nice breeze in La either.

Oh well, she's been nice to watch and wonder from...
Member Since: Posts: Comments:
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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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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