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 FLdewey:


My name is Dewey, not Buddy.

Yes I have been bracing myself against the half inch of rain I've received today. It's a miracle I'm still connected to the


OMG..!


We lost Kenny..

I mean Dewey
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Quoting Patrap:
Off shore from Coral Gables ,Naples area.


WNW



and see the circulation right below Naples?
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As long as the surface circulation is closed this is still a tropical cyclone, but may not remain one all the way to the north gulf coast. Either way, whether it's an open wave or not, weather effects will be the same. Some rain squalls and that's it. This is a ragged system as expected and will all but die in the gulf. Strengthening isn't likely.
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Quoting centex:
Re-posted in new blog because I ended up in the dregs of old blog. For those ignoring Caribbean wave.

We should be more sensitive to tropical waves moving west through Caribbean. I think it's supose to eventually move into bay of Campeche before turning N into S Texas. Local NWS mets watching it for rain.


That must be what CMC and ECMWF have been trying to show for awhile.
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We will know for sure by morning if Bonnie has passed away. She may get up on the count of 9.
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54. IKE
Fort Myers is within 25 miles of the new coordinates.....

Fort Myers, Florida (Airport)
Updated: 13 min 12 sec ago
Overcast
81 °F
Overcast
Humidity: 91%
Dew Point: 78 °F
Wind: 13 mph from the NE
Pressure: 29.89 in (Steady)

Heat Index: 89 °F
Visibility: 10.0 miles
UV: 2 out of 16
Pollen: 3.90 out of 12
Pollen Forecast new!
Clouds:
Few 800 ft
Mostly Cloudy 2500 ft
Overcast 3700 ft
(Above Ground Level)
Elevation: 16 ft
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Bonnies head has been ripped off and strewn across FL after fighting shear all week. By the look of the sat pics and shear forecast maps it does not look like she will do much even though the circulation is there. See how it goes over the next 6-12 back over the water.
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...Cant ya hear my heart beat,,itsa Love Beat,..
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Whew, thank god they moved all of the drilling equipment and oil recovery vessels!
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Off shore from Coral Gables ,Naples area.


WNW


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47. IKE
This is a TD?



Member Since: June 9, 2005 Posts: 23 Comments: 37860
Sorry if its already been said/asked is that naked swirl moving west south of the convection Bonnie's coc?

Isnt that how she started out? Maybe we've come full circle with her. :)
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Hi Atmos...well, looks like many of us now doubt this Bonnie will regather and recompose her self to carry on the forcast track....
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44. IKE
Quoting atmosweather:


No deep convection anywhere near the center...just a couple of light rainbands. It's not really a tropical cyclone anymore and with this environment staring it in the face I would doubt that any reorganization over the GOM is possible...it only has a day or so to do this, and when the storm is this decoupled and ill-defined it is just not likely.


I agree with you. I just looked at buoys within 60 miles of the listed coordinates. Nothing much there.

Spurious Bonnie may be true.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Try explaining to your better half that you cant talk on the Phone right now cuz your reading a
Pouch discussion.

Thanx for that one Drak
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Quoting Patrap:
Womp, waaaaaaaaaaaaa........

HOWEVER...DEGENERATION INTO AN OPEN TROUGH IS ALSO POSSIBLE.




Quoting Tazmanian:
HOWEVER...DEGENERATION INTO AN OPEN TROUGH IS ALSO POSSIBLE.


i think its a open trough right now

Look at the vis sat loop. there is an obvious but naked LLC at 26N 81.7W or right about over FT Myers..
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This blog is so much fun :)
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Re-posted in new blog because I ended up in the dregs of old blog. For those ignoring Caribbean wave.

We should be more sensitive to tropical waves moving west through Caribbean. I think it's supose to eventually move into bay of Campeche before turning N into S Texas. Local NWS mets watching it for rain.
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Quoting thewindman:
[snip, your welcome]
On a scale of 1 to 10 of useful post, that required lowering the definition of what qualifies as a 1.

(Unless, maybe, that was sarcasm?)
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Quoting IKE:
Oh my....



No deep convection anywhere near the center...just a couple of light rainbands. It's not really a tropical cyclone anymore and with this environment staring it in the face I would doubt that any reorganization over the GOM is possible...it only has a day or so to do this, and when the storm is this decoupled and ill-defined it is just not likely.
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Not saying Bonnie will do this, but let's say it goes bak to an open wave then gets bak to a TD o even a TS before it makes landfall in a Gulf State, would it then become TD 4 or Collin?
Thanks in Advance.
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Dont go away empty handed shoppers,..

We have a consolation prize..!


Time until Friday, December 21, 2012 at 11:11:11 AM (UTC time)
881 days
21158 hours
1269493 minutes
76169615 seconds
Alternative version

It is 881 days, 14 hours, 13 minutes and 35 seconds until Friday, December 21, 2012 at 11:11:11 AM (UTC time)
Current time is

Friday, July 23, 2010 at 20:57:36 UTC
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Man...she's really picking up steam now...Cat 1 by nightfall....

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Can't believe they even named this storm. Never more than a cluster or clouds. Again what an overhyped year. Almost August now
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Thank you Dr Master's for the fresh new blog and update.

I am not a "down caster" but I just do not think it will stay on that forcast track...

but I've been wrong before ... but I think Bonnie looks pretty bad...but maybe she will perk up a bit in the GOM...

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Quoting IKE:
Oh my....



There's a Hole in the GOM where a Hurricane should be..?

Saved by da ULL from Up above.

..literally.

I'll drink to dat.

.
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Any easing of this thing for the oil disaster area will be welcome in my mind. I just want this thing to die, and give those poor folks and critters a break. Think: Dry air and high shear.
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Thanks for the update.
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Current surface obs:

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The Pouch tracking website now has discussion on the systems it is monitoring. If you click on "Pouch synopses (EOL PREDICT Catalog)" it will take you to the daily report page.
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23. IKE
Oh my....

Member Since: June 9, 2005 Posts: 23 Comments: 37860
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Quoting FLdewey:
She's not looking good at all... she needs a Redbull


Thats what Im sayin!!
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Bonnie..

A degenerate,..?

O man..

Im glad I dont use sarcasm..
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Womp, waaaaaaaaaaaaa........

HOWEVER...DEGENERATION INTO AN OPEN TROUGH IS ALSO POSSIBLE.


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17. IKE
TROPICAL DEPRESSION BONNIE DISCUSSION NUMBER 6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032010
500 PM EDT FRI JUL 23 2010

SATELLITE IMAGERY AND RADAR OBSERVATIONS INDICATE THAT BONNIE HAS
BECOME LESS ORGANIZED WHILE MOVING INLAND OVER SOUTHERN FLORIDA.
THE CENTER IS TO THE SOUTHEAST OF AN AREA OF SHAPELESS DEEP
CONVECTION. GIVEN THE CURRENT ORGANIZATION AND SURFACE
OBSERVATIONS...THE INITIAL INTENSITY HAS BEEN LOWERED TO 30 KNOTS.
THE ENVIRONMENT IN THE GULF OF MEXICO IS FORECAST TO REMAIN
UNFAVORABLE FOR STRENGTHENING MAINLY DUE TO STRONG WIND SHEAR. WITH
THE EXCEPTION OF THE STATISTICAL MODELS WHICH BRING THE WINDS UP A
LITTLE BIT...NONE OF THE DYNAMICAL GUIDANCE RESTRENGTHENS BONNIE IN
THE GULF OF MEXICO. BASED ON CONTINUITY AND THE STATISTICAL
MODELS...THE OFFICIAL FORECAST CALLS FOR SLIGHT STRENGTHENING
BEFORE THE CYCLONE APPROACHES THE NORTH GULF COAST LATE SATURDAY.
HOWEVER...DEGENERATION INTO AN OPEN TROUGH IS ALSO POSSIBLE.

THE CENTER OF BONNIE HAS BEEN RAPIDLY CROSSING THE SOUTHERN FLORIDA
PENINSULA ABOUT 300 DEGREES OR WEST-NORTHWEST AT 16 KNOTS DURING
THE PAST FEW HOURS. BONNIE IS EMBEDDED WITHIN WELL-DEFINED
STEERING CURRENTS ASSOCIATED WITH THE FLOW BETWEEN A HIGH PRESSURE
SYSTEM OVER THE UNITED STATES AND AN UPPER-LOW OVER THE WESTERN
GULF OF MEXICO. THIS PATTERN IS FORECAST TO PERSIST...KEEPING
BONNIE ON THE SAME GENERAL TRACK THROUGH THE NEXT 2 TO 3 DAYS.IF
BONNIE SURVIVES AS A TROPICAL CYCLONE...ONLY A SMALL DECREASE IN
THE CURRENT FORWARD SPEED IS ANTICIPATED. SINCE THE STEERING
CURRENTS ARE WELL DEFINED AND THE GUIDANCE IS TIGHTLY CLUSTERED
THERE IS A GOOD CONFIDENCE IN THE TRACK FORECAST.


FORECAST POSITIONS AND MAX WINDS

INITIAL 23/2100Z 26.2N 81.9W 30 KT
12HR VT 24/0600Z 27.5N 84.5W 30 KT
24HR VT 24/1800Z 29.0N 87.5W 40 KT
36HR VT 25/0600Z 30.5N 90.0W 35 KT...INLAND
48HR VT 25/1800Z 31.5N 91.0W 25 KT...INLAND
72HR VT 26/1800Z 33.5N 93.0W 20 KT...POST-TROP/REMNT LOW
96HR VT 27/1800Z...DISSIPATED

$$
FORECASTER AVILA/ROBERTS
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Whew, thank god they moved all of the drilling equipment and oil recovery vessels!
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.."And now,,the end iz near,

I feel I face, My Final Advisory"..
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13. IKE
The end may be near for bumbling Bonnie....

Member Since: June 9, 2005 Posts: 23 Comments: 37860
http://blogs.chron.com/sciguy/archives/2010/07/live_chat_tropical_storm_bonnie.html

This guy from the houston chronicle does a good job on tracking hurricanes without the hype.
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Quoting NewBdoBdo:
Hi Pat...how was your roast beef?


Eggcellent.


Almost as good as the Popeyes chicken too
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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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