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 StormW:
Ok, just one or two more things, then we'll let some folks go back to their fantasy.

What did 2002, 2004, and 2009 have in common?


an a la nina that was preceeded by two years of el nino
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Quoting Levi32:
This coming downward MJO pulse will likely not be as strong or as long as the GFS operational has it right now.


Yeah I'd be surprised if it verified this time since it hasn't most of the season. A 10-20 day weak downward phase is most likely.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
So you mean to tell me, all those people who like to surf in Hawaii (which, ironically, is surrounded by....Ocean) aren't really catching "waves"? Hmp. Learn something new everyday.
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-_-
Member Since: November 1, 2004 Posts: 25 Comments: 8923
Quoting Tazmanian:



i think this guy sould be dr m back up when dr m go a way for 2 weeks
now THAT's funny!
Member Since: November 1, 2004 Posts: 25 Comments: 8923
Quoting homelesswanderer:


El nino? Lol sorry just got bk on the blog. :)


Lol, only 1 named storm by the end of July (well 2009 only had a TD)
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storm,
are there going to be very few hurricanes like last year?
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Tornado reported in Escambia County FL with damage to a home

Member Since: January 24, 2010 Posts: 0 Comments: 529
200. IKE
Memo to NHC: Please put bumbling Bonnie out of her misery on the next advisory....it's over...admit it...remnant low.....TIA!

IKE...amateur WU blogger...celebrating 5 years of useless posts....

$$


Member Since: June 9, 2005 Posts: 23 Comments: 37858
198. JLPR2
What was this thing that crossed PR today?


It brought the strongest thunderstorm my area has experienced so far this year, I even lost power for like 30minutes.
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This coming downward MJO pulse will likely not be as strong or as long as the GFS operational has it right now.
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Quoting fallinstorms:


no, the weather pattern is to horrible this whole year for one storm! alex got lucky real lucky. alex is the strongest this year. the rest will die like bonnie.





i think this guy sould be dr m back up when dr m go a way for 2 weeks
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194. jscs
Quoting Tazmanian:
i made 500+ commets this for a weak TS Bonnie



So you're officially one of the most annoying people on here, then.
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Quoting StormW:


Don't know...haven't looked in a few hours. I'll take a look later on this eve.


looks a little persistent... but looks like sheer might kill it anyway..
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Quoting StormW:
Ok, just one or two more things, then we'll let some folks go back to their fantasy.

What did 2002, 2004, and 2009 have in common?


El nino? Lol sorry just got bk on the blog. :)
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Quoting StormW:
Ok, just one or two more things, then we'll let some folks go back to their fantasy.

What did 2002, 2004, and 2009 have in common?
El Nino years
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Quoting Orcasystems:
Not much happening... yet... hmmm where are all of the NOLA panic casters?



AOI

AOI

AOI

AOI

Landfall Points

TS BUSTED FORECAST ALIBI
did they jump the gun nah precautions and preps is important and a drill everyonce in a while is not a bad thing
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Quoting sammywammybamy:


IVE HAD ENOUGH OF YOUR CAARRP(SPELLED WRONG PURPOSELY)

POOF




what that needed
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No waves in the ocean huh? Interesting...
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Quoting centex:
WU help. I have two issues. Sent in helpdesk ticket on WU web cam issue. Worked for years but stopped working couple of weeks ago. Did they change something? Also have issue with WU radar links like those posted this blog. It crashes my web authoring tool.



why are you posting that here?
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Quoting fallinstorms:


yes

alex will be the only hurricane

Who died and left you their crystal ball, hope you're right pal!
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Quoting StormW:


I like you...u funny!


Hey Senior Chief Caster.... is that wave down south of the Dominican any thing to worry about????
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WU help. I have two issues. Sent in helpdesk ticket on WU web cam issue. Worked for years but stopped working couple of weeks ago. Did they change something? Also have issue with WU radar links like those posted this blog. It crashes my web authoring tool.
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How do you ignore someone? I've already attempted to click on the ignore button before but it didn't work.
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Quoting fallinstorms:
there are no waves in the ocean

the dust is getting them

africa is so try
we might not even see a wave off of it


I guarantee there are waves in the ocean...
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163. fallinstorms

there are no waves in the ocean


I got some surfer buddies that are gonna be P.O'd at this news...
Member Since: November 1, 2004 Posts: 25 Comments: 8923
Way too much emphasis being put on to the downward MJO...
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Just want remind anyone who think this season is a bust. their memory is very short, just remember 2004, No storm until August 1 and that was a year to remember! Hopefully it will end with Bonnie, but thats wishful thinking on my part anyway.
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fallinstorms do you think we will see 30 name storms this year
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Quoting StormW:


That means in our area of the world, sinking air in the Gulf, Caribbean. Not conducive for storm development.
How often do hurricanes form during the downward motion of the MJO?
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168. xcool
ha
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163. fallinstorms

there are no waves in the ocean

Oh...K....
Member Since: November 1, 2004 Posts: 25 Comments: 8923
lol i like this guy he funny
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Quoting fallinstorms:
there are no waves in the ocean

the dust is getting them

africa is so try
we might not even see a wave off of it



try you mean dry
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Quoting connie1976:



what does that mean?


A downward MJO phase in the Atlantic Basin basically means that the air over the Caribbean and Atlantic will be sinking instead of rising...and sinking air usually indicates a pattern of subsidence and thus less tropical development.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
Quoting tkeith:
If you turn out to be right...you'll be my new best friend



that was a joke right your kinding right
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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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