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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1261. centex
Give Bonnie until morning. She has fought off bad environment before. Granted she does not look good tonight.
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1260. Levi32
Quoting wfyweather:


theres a closed circulation... Look at HH obs they found west winds.. its a td.

U serious? ITS SHOWING LITTLE PRCIP BECAUSE ITS OVER WATER AND FAR FROM THE RADAR SITE!


Or this?

Member Since: November 24, 2005 Posts: 635 Comments: 26647
OK heres how I look at it... the National Hurricane Center is mentioning that the possibility of this thing degenerating into an open wave definitely exists... but for right now its still a td and if dmax can help it fire new convection it could also definitely reach 40-45 mph ts... and there ultimately going to go with the route thats going to cause people to take safety meausures.. and thats ultimately the route they should take.
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1258. pottery
Quoting wfyweather:


theres a closed circulation... Look at HH obs they found west winds.. its a td.

U serious? ITS SHOWING LITTLE PRCIP BECAUSE ITS OVER WATER AND FAR FROM THE RADAR SITE!

When did the recon find the west wind?
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1257. Levi32
Quoting atmosweather:


Looks like there isn't really a surface feature there...I think it's a portion of the wave that moved through the islands 2 days ago that just degenerated...but the ULL and the associated mid/upper energy along with the upper divergence is helping convection fire down there. This must be watched later this weekend.


Indeed, and there is some turning at the 500mb level in its northern portion north of the Dominican Republic, but any center of the disturbance may ultimately materialize farther south.

Member Since: November 24, 2005 Posts: 635 Comments: 26647
Well, when is the next one coming? Any ideas?
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Quoting SLU:


Yeah I remember those systems very well.

I guess they don't want to go about naming every blob on the satellite pics but if a systems meets the specifications then it should be classified accordingly.

I'd like to see less confusion in years to come. It's been happening a lot more these days than say 10 years ago which it strange giving that we have more technology and research to aid us.


u do know that the nhc has extremly better satelite loops then they provided for us the ones we link here isa joke lol trust me they know there stuff
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Quoting wfyweather:


theres a closed circulation... Look at HH obs they found west winds.. its a td.

U serious? ITS SHOWING LITTLE PRCIP BECAUSE ITS OVER WATER AND FAR FROM THE RADAR SITE!


Don't shoot the experts.
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1253. Levi32
Quoting SLU:


Yeah I remember those systems very well.

I guess they don't want to go about naming every blob on the satellite pics but if a systems meets the specifications then it should be classified accordingly.

I'd like to see less confusion in years to come. It's been happening a lot more these days than say 10 years ago which it strange giving that we have more technology and research to aid us.


Exactly. Consistency one way or the other is all I would like to see.....far better than making a different call on every storm.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
Quoting Levi32:
No significant wind shift at the surface with the wave near Hispaniola on the new ASCAT pass.



Looks like there isn't really a surface feature there...I think it's a portion of the wave that moved through the islands 2 days ago that just degenerated...but the ULL and the associated mid/upper energy along with the upper divergence is helping convection fire down there. This must be watched later this weekend.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting Asta:
Anyone had a favorite forecast for expected rainfall amounts from BONNIE?


1" maybe locally 2" if that.
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Quoting pottery:

Not seeing a closed circulation............


theres a closed circulation... Look at HH obs they found west winds.. its a td.
Quoting Levi32:
Radar shows a broad, ill-defined center with almost no precip.



U serious? ITS SHOWING LITTLE PRCIP BECAUSE ITS OVER WATER AND FAR FROM THE RADAR SITE!
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1249. SLU
Quoting CybrTeddy:


There were several storms in 2009 that should have been classified.. 90L and 91L most noticeably in Late May - Early June. 2009 should have had 11 named storms imo. 2008 should have had 17, there was a low off the coast of the East coast that was organized enough that the hurricane hunters sent a vortex message, never became a named system. But they are the NHC, they know what they're doing.


Yeah I remember those systems very well.

I guess they don't want to go about naming every blob on the satellite pics but if a systems meets the specifications then it should be classified accordingly.

I'd like to see less confusion in years to come. It's been happening a lot more these days than say 10 years ago which it strange giving that we have more technology and research to aid us.
Member Since: Posts: Comments:
1248. Asta
Anyone had a favorite forecast for expected rainfall amounts from BONNIE?
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1247. Levi32
Radar shows a broad, ill-defined center with almost no precip.

Member Since: November 24, 2005 Posts: 635 Comments: 26647
A TROUGH OF LOW PRESSURE OVER THE SOUTHEAST BAHAMA ISLANDS IS
FORECASTED BY THE SHORT RANGE MODELS TO MOVE WEST NORTHWEST AND
THROUGH SOUTH FLORIDA ON SATURDAY. AT THE SAME TIME...THE DEEP
TROPICAL MOISTURE WILL REMAIN IN PLACE WITH PWAT VALUES AROUND 2.2
TO 2.4 INCHES. SO HAVE INCREASE THE POPS A LITTLE BIT TO NUMEROUS
CONDITIONS OVER ALL OF THE CWA ON SATURDAY ALONG WITH LOCALLY
HEAVY RAINFALL.

ANOTHER TROPICAL WAVE OVER THE EASTERN CARIBBEAN SEA WILL ALSO
MOVE TO THE WEST NORTHWEST AND THROUGH SOUTH FLORIDA LATE SUNDAY
INTO MONDAY. THIS WILL KEEP THE TROPICAL MOISTURE IN PLACE ALONG
WITH SCATTERED POPS FOR SUNDAY AND MONDAY.


hmmmm?
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Quoting wfyweather:


doesnt matter what it looks like man... there finding strong enough winds and a closed circ.... case closed


Danny from last year looked worse than this.
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1244. pottery
Quoting wfyweather:


doesnt matter what it looks like man... there finding strong enough winds and a closed circ.... case closed

Not seeing a closed circulation............
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1243. Patrap
Quoting gordydunnot:
Patrap that's the clearest I have seen your radar in a year.


Its the wundergrounds radar.
Mines in the truck..But the Doppler Dish is Cracked..
again
Member Since: July 3, 2005 Posts: 424 Comments: 128279
1242. Levi32
No significant wind shift at the surface with the wave near Hispaniola on the new ASCAT pass.

Member Since: November 24, 2005 Posts: 635 Comments: 26647
Patrap that's the clearest I have seen your radar in a year.
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Hurrkat was right about Bonnie, no more than a 40 mph TS.
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Quoting hunkerdown:
the NHC is criticized by many on here for every decision they make on every puff of clouds that roll through the atlantic basin from late may through early december...
Quite true, and often amusing. Sorry if I sounded too serious in my post but as Patrap posts often, the NHC has a mission statement which most who criticize probably have never read.
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Quoting Levi32:
At any rate, this doesn't look like a tropical cyclone:



doesnt matter what it looks like man... there finding strong enough winds and a closed circ.... case closed
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1237. KEEPEROFTHEGATE (Mod)
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Quoting chrisdscane:


in the end their mostly right u gota admit
or, thats why they are there and we are here...
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1235. Levi32
At any rate, this doesn't look like a tropical cyclone:

Member Since: November 24, 2005 Posts: 635 Comments: 26647
1234. Patrap
Dem radars are kinda new spiffy tings I hear..

LOL



Member Since: July 3, 2005 Posts: 424 Comments: 128279
May have something interesting to watch come Sunday maybe?
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Quoting wfyweather:


I'm sorry... I didn't know you could see the future? the convection has already fired up once... It can do it again


Not at all...I am going by what I see and what I know is causing it. If I am wrong I will always take it in stride.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting SLU:


There you go.

So technically we're still on course for an 18 - 23 year.

In all seriousness the numbers have been messed up badly already this year if we have to go strictly by the book which we should anyway ...


There were several storms in 2009 that should have been classified.. 90L and 91L most noticeably in Late May - Early June. 2009 should have had 11 named storms imo. 2008 should have had 17, there was a low off the coast of the East coast that was organized enough that the hurricane hunters sent a vortex message, never became a named system. But they are the NHC, they know what they're doing.
Member Since: July 8, 2005 Posts: 259 Comments: 24020
Quoting hunkerdown:
the NHC is criticized by many on here for every decision they make on every puff of clouds that roll through the atlantic basin from late may through early december...


in the end their mostly right u gota admit
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Quoting Ossqss:


You are right on that,,,, oh my!



TONS of TVS popping everywhere, lucky none that have been sustained very long, yet...
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Alright... there are a couple of things I want to note.... 1. This low is still closed... so if it fires up more convection it will have NO PROBLEM strengthenin one again into TS Bonnie...
2. It is moving further West than most models showed... hopefully that stops so I can have a a successful intercept in New Orlenas
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1227. Ossqss
Quoting VAbeachhurricanes:


Iowa, Pennsylvania, New York. hold on to your hats, its gonna be a restless night. Gracious thats a big MCC in MINN, SD...


You are right on that,,,, oh my!

Member Since: June 12, 2005 Posts: 6 Comments: 8186
1226. Patrap
TVS-Palooza

NEXRAD Radar
Sioux Falls, Base Reflectivity 0.50 Degree Elevation Range 248 NMI

Member Since: July 3, 2005 Posts: 424 Comments: 128279
1225. SLU
Quoting CybrTeddy:


If NHC went with the TS winds found in TD2 right before landfall we'd be looking at 5 named storms right now.


There you go.

So technically we're still on course for an 18 - 23 year.

In all seriousness the numbers have been messed up badly already this year if we have to go strictly by the book which we should anyway ...
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Quoting Tazmanian:




a overhyped caster


Hey finally someone I completely agree with. 2 months gone by and all we have is one hurricane and one cluster of thunderstorms that they named just so they can pretend it is an active year
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Quoting atmosweather:
Couple of SSW-erly winds... they will probably just assume they didn't sample an area (however microscopic) where there are in fact W winds and will keep it going until 5am. By that time there will be no organized deep convection within 100 miles of the center and the LLC will have dissipated, so they will have to declassify.


I'm sorry... I didn't know you could see the future? the convection has already fired up once... It can do it again
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Quoting Ossqss:
Clickable to lengthen



Interesting model to watch :)





Hello there?
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1221. pottery
Quoting hunkerdown:
maybe thats all the little fella had...how do you know the equine was not deceased BEFORE he picked up the hammer

Well, I would need to do a complete autopsy to detirmine the Time OfDeath.
If it can be shown that the Equine was alive BEFORE the Hammer incident, charges may be laid in this matter.
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Couple of SSW-erly winds... they will probably just assume they didn't sample an area (however microscopic) where there are in fact W winds and will keep it going until 5am. By that time there will be no organized deep convection within 100 miles of the center and the LLC will have dissipated, so they will have to declassify.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting jlp09550:


Relocation or is Bonnie falling apart?


Believe this means we have seen the end.
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1218. Patrap
Member Since: July 3, 2005 Posts: 424 Comments: 128279
Quoting LightningCharmer:
NHC is not in a contest with anyone or anything. They're job is to save lives and protect property among other things.

Not that they're beyond criticism but please don't criticize them for winning or losing some unmentioned contest of classifying or declassifying. The contests are for those of this blog with each other IMHO.
the NHC is criticized by many on here for every decision they make on every puff of clouds that roll through the atlantic basin from late may through early december...
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Quoting jlp09550:


Relocation or is Bonnie falling apart?


or worse.. the dreaded almost westerly winds.
Member Since: October 1, 2007 Posts: 81 Comments: 26511
1215. KEEPEROFTHEGATE (Mod)


maybe new area big to follow
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1214. Levi32
Quoting centex:
We are debating this comment - THE INTENSITY FORECAST IS BASED ON THE PREMISE THAT ENOUGH CONVECTION WILL RE-DEVELOP TO CAUSE SLIGHT
STRENGTHENING BEFORE BONNIE REACHES THE NORTHERN GULF COAST. AN INCREASINGLY LIKELY ALTERNATIVE SCENARIO IS THAT THE CYCLONE WILL DECAY TO A REMNANT LOW OR OPEN TROUGH SOMETIME ON SATURDAY.

So remant low forecast does follow NHC, sorry.


Nope. In the end their forecast is for intensification.

FORECAST POSITIONS AND MAX WINDS

INITIAL 24/0300Z 26.4N 83.4W 30 KT
12HR VT 24/1200Z 27.7N 85.7W 30 KT
24HR VT 25/0000Z 29.2N 88.5W 35 KT
36HR VT 25/1200Z 30.5N 90.5W 35 KT...INLAND
48HR VT 26/0000Z 31.4N 91.8W 25 KT...INLAND
72HR VT 27/0000Z 34.0N 93.0W 20 KT...POST-TROP/REMNT LOW
96HR VT 28/0000Z...DISSIPATED
Member Since: November 24, 2005 Posts: 635 Comments: 26647
lol weres bonnie?
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AOI
Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting Orcasystems:
Oh no Mr Bill, say it ain't so...


AOI


Relocation or is Bonnie falling apart?
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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.