Tropical Storm Bonnie Makes Her Debut

By: Dr. Jeff Masters , 4:32 AM GMT on July 23, 2010

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Hi everybody, this is Dr. Rob Carver filling in for Jeff on the late shift.

Based on information from Hurricane Hunters, the National Hurricane Center upgraded TD Three to Tropical Storm Bonnie. As of the 11PM EDT advisory, Bonnie was at 23.4N, 76.5W which is 285 miles southeast of Miami, Florida. Bonnie has maximum winds of 40 mph, a minimum central pressure of 1007 mb, and is moving to the northwest at 14 mph. Bonnie will pass over the Everglades/Florida Keys Friday and cross into the Gulf of Mexico Friday night/early Saturday morning. Tropical storm warnings are in effect for both Florida coasts south of Lake Okeechobee to Key West.


Fig. 1 IR satellite image of Tropical Storm Bonnie at 1216AM EDT.

Threats
NHC is expecting 2-4 inches of rain over south Florida due to Bonnie and 3-5 inches over the Bahamas. They are forecasting a storm surge of 1-2 feet. Tropical storm force winds are expected in the Bahamas starting Thursday night, and they are forecast to arrive in southern Florida Friday morning.

Impacts and Emergency Preparedness
As of 1130PDT EDT, the Key West NWS office is indicating that there are no evacuation orders in effect or planned for Monroe County (the Keys). Small craft are being advised to stay in port and be well secured to their docks. Two shelters will be opened, Key West High School and Stanley Switlik Elementary School in Marathon.

Most of the ships at the Deepwater Horizon oil spill site and other skimming ships have been ordered to seek safe harbor. In the statement, Adm. Allen said ships that operate the ROVs will be the last out and the first back to keep the wellhead observations going as long as possible.

Forecast/Model Assessment
The track models and ensemble models show remarkably good agreement for Bonnie's path across south Florida and towards southeast Louisiana. The current intensity forecast calls for Bonnie to maintain strong tropical storm force winds (40-50 knots) until it makes landfall in Louisiana, with a 15% chance of becoming a hurricane before then. However, the global models (GFS, Canadian GEM, NOGAPS) and the hurricane dynamical models (GFDL, Navy GFDL, and HWRF) do not intensify Bonnie at all. The statistical models (SHIPS and LGEM) support the intensity forecast.

I'm inclined to take the predictions of global and dynamical models with a large grain of salt. When I reviewed the latest model runs (18Z and 12Z), it was apparent that none of the models had a good initialization of Bonnie's structure. Bonnie has a relatively small circulation, so it's easy for the models' initialization to act like there isn't much of a storm there. Without accurate starting conditions, any model will have trouble producing an accurate forecast. NHC has a good summary of the different forecast models they use.

Next Update
Jeff will have an update sometime Friday morning.

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197. 7544
how long will the hh be in bonnie ?
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Quoting homelesswanderer:


OK. What is the current run? I never get that strait.


Current run is 00z but some of the models haven't come in yet for 0z like the GFDL and HWRF which will be out within the hour.
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Quoting MississippiWx:


Could that be an old center that Bonnie shed and a more dominant one has developed farther north underneath the mid level center? Satellite imagery is starting to look too good for this system to not be vertically stacked.


I was kinda thinking the same thing. The 11pm NHC advisory mentioned something about a more northward component.
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Whew! Bonnie is moving fast. Link
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Quoting cchsweatherman:
Recon will soon tell the truth regarding the low level circulation and whether or not its underneath the convection. I really don't see how a storm could be organized with such a satellite appearance without a low level circulation underneath the main convective mass.


This reminds me of Ernesto, went it was in the florida straits.
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191. xcool
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Quoting cchsweatherman:
Recon will soon tell the truth regarding the low level circulation and whether or not its underneath the convection. I really don't see how a storm could be organized with such a satellite appearance without a low level circulation underneath the main convective mass.


I've seen it...lol.
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It's finding warmer waters now, but when that small sfc siphon finds the Gulf Stream, make no mistake, she's gonna get a bit fatter. Convergence and divergence should be improving - but quite weak right now, weak mostly because of its small size - it's there but only a small area of converging inflow. Another confirmation that the llc is struggling to come to life and get concentric with the stronger mid (mostly) and upper level vortices.

Convergence/Divergence

850mb vorticity also still indicates elongated sfc characteristics. 500mb vorticity is the only symmetric level and should also indicate the mid-level spin is more dominate, im.
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Quoting cchsweatherman:
Recon will soon tell the truth regarding the low level circulation and whether or not its underneath the convection. I really don't see how a storm could be organized with such a satellite appearance without a low level circulation underneath the main convective mass.
Yeah really would be odd if it is that decoupled. Watching the RGB loop makes me want really believe its decoupled, but the IR appearance is pretty nice.
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Quoting txsweetpea:


Still a bit of a left shift, correct?


Not much of a change from the last cycle actually except that the BAM suite shifted right. Compared to yesterday though everything is shifted much farther left.

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Quoting Stormchaser2007:
Interesting shape.



Okay, here's the deal. Looking at the image in post 156, if the center is E of Andros, this storm is under that organized convection, and we are talking about a storm that could be strengthening faster than the NHC official forecast. But if its SE of Andros, then this is not as strong as it looks.

I heard some mention of ASCAT passes going around. Does anyone have a link, I want to see the latest pass and the time at which the pass was taken.
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So I go out and pick up my kid from the bowling ally and get back and she is looking better than she has all day... this storm wants to keep us all guessing. Just like a woman to change her attire 30 times before going out for the big evening teehee :)
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if you watch the rainbow IR water vapor and the shortwave it seems there are the main bands coming out of the east and west and what i think looks like outflow to the south but i see no COC outside the main convection im going to believe its there if i am wrong- arnt we all sometimes but dont shun me for this i am still nothing but a incoming freshman into atmo sci who knows only a little more than your average joe
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tennisgirl08: It has strengthened because of warm waters and lower shear.
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Quoting NCHurricane2009:


That CLP5 model of 97L/Bonnie is obssessed with curving it northward a lot sooner and bringing it in my neighborhood, LOL. Its definetly been an eastern outlier, that model needs some fixing, LOL.


It's meant to do its own thing. It's not a model. It's a simulation of where a storm in this position at this time of year would be likely to go based on climatology. Normally these storms would tend to curve up east of Florida, but the abnormal amount of ridging over the SE US this year because of the La Nina is steering stuff farther west before recurving.
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Quoting homelesswanderer:
Photobucket" width="600" height="400

Why the left shift?
thats old
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Quoting Levi32:


Yup....and new ASCAT pass is a dead giveaway.


Could that be an old center that Bonnie shed and a more dominant one has developed farther north underneath the mid level center? Satellite imagery is starting to look too good for this system to not be vertically stacked.
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Quoting Levi32:


That's the last image from 97L, notice the position farther east than Bonnie is at right now. Here's the current models:



OK. What is the current run? I never get that strait.
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Recon will soon tell the truth regarding the low level circulation and whether or not its underneath the convection. I really don't see how a storm could be organized with such a satellite appearance without a low level circulation underneath the main convective mass.
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Quoting Levi32:


That's the last image from 97L, notice the position farther east than Bonnie is at right now. Here's the current models:



Still a bit of a left shift, correct?
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Quoting islandeye:
salutations all, tired of being a lurker...long-time fan of the blog, and am in the path of this one, so thought it'd be as good a time as any to say hello.

Hey there. :)
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Levi, how can it sustain that shape if its not over the center?
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Quoting atmosweather:
Levi do you think the COC is where I think it is...at around 23.6N 77.2W?..Maybe a little E of there? I was looking at the RGB loop.


I just put my face to my laptop screen and stared at the RGB loop for a couple minutes and it's hard to tell. I'd say it's farther west, closer to 77.5W and maybe a little farther south at 23.4N, but again hard to tell.
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Quoting Levi32:


That's the last image from 97L, notice the position farther east than Bonnie is at right now. Here's the current models:



That CLP5 model of 97L/Bonnie is obssessed with curving it northward a lot sooner and bringing it in my neighborhood, LOL. Its definetly been an eastern outlier, that model needs some fixing, LOL.
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Thats weird. Recon leveled off at 10k feet, now went down to 5k feet.
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P451 - cool loop. i think bonnie is not being affected by the ULL at the moment and is definitely strengthening.
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Quoting Stormchaser2007:
Interesting shape.



That's quite a shape out of a supposed exposed LLC. I'd be running for the hills if I didn't know any better.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Stormchaser, that shape is primed for higher winds. It isn't in a mountain valley of Cuba!
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Quoting homelesswanderer:
Photobucket" width="600" height="400

Why the left shift?



I would like to know also...hmmmmm
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Hurricane Hunters are off the South Florida coast and halfway between Florida and Andros Island. Approaching the storm soon. Recording 30-35 mph winds thus far.
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161. xcool
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160. 7544
looks better there stromchaser
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Quoting homelesswanderer:
Photobucket" width="600" height="400

Why the left shift?


That's the last image from 97L, notice the position farther east than Bonnie is at right now. Here's the current models:

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Looks like RECON will go in at 10,000 feet.
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I'm thinking top winds in Bonnie are around 58 miles per hour now.
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Interesting shape.

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155. xcool
homelesswanderer OLDDDDDDD
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Quoting homelesswanderer:
Photobucket" width="600" height="400

Why the left shift?


Grab the storm03 models, those are WAY old.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting atmosweather:
The surface COC is definitely exposed still and not under the convection IMO...take a look here and watch near 23.6N 77.2W.


Yup....and new ASCAT pass is a dead giveaway.
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151. xcool
Goldenblack .I;M very tired after a long day
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http://www.ndbc.noaa.gov/show_plot.php?station=spgf1&meas=wdpr&uom=E&time_diff=-4&time_label=EDT
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Photobucket" width="600" height="400

Why the left shift?
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Quoting pfdfirefighter:
Gys what about the blow up of convection in the Bay of Campechee Spelling bites I know. People said something earlier about one of the models forecasting two storms, Just noticed the blow up and if the upper level low get west of it it may get pulled east back into th Gulf Of Mexico.
Dont kill me for the post just wanting others thoughts.


That tropical wave nearly developed into Colin and would have if it had another day over water. It is moving inland now and will continue westward into Mexico. It's a disastrous rain event for them yet again.
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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.