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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SUMMARY OF 500 AM EDT...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...24.1N 78.6W
ABOUT 155 MI...250 KM SE OF MIAMI FLORIDA
ABOUT 165 MI...260 KM ESE OF MARATHON FLORIDA
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/HR
PRESENT MOVEMENT...WNW OR 295 DEGREES AT 18 MPH...30 KM/HR
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES

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TROPICAL STORM BONNIE NEAR 23.4N 76.5W 1007 MB AT 0300 UTC IS
MOVING NW AT 12 KT. MAXIMUM WINDS 35 KT WITH GUSTS TO 45 KT.
LATEST NHC ADVISORY FORECASTS BONNIE THROUGH THE FLORIDA KEYS
LATER TODAY AND STRENGTHENS SLIGHTLY...THEN MOVES INTO THE GULF
OF MEXICO TONIGHT. OTHERWISE HIGH PRES RIDGE ALONG 30N/31N WILL
CONTINUE THROUGH THE WEEKEND INTO EARLY NEXT WEEK...WITH ELY
WINDS 15-20 ALONG THE SOUTHERN PERIPHERY OF THE S OF AROUND 24N.


If she's at 23 or 24 hows she going to move wnw with easterly winds. Lol. I give up. Guess I'll shut up watch. :)
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Quoting BahaHurican:
Morning atmo. I have a feeling they got somewhat more rain in Exuma and South Andros than we did here. However, I'm very glad it wasn't any worse. This was a best case scenario for us.

With Bonnie fleeing the scene, my biggest concern right now is that this track or one similar to it will happen with a much larger more powerful system in a few weeks. It often happens once the synoptic pattern gets "set".

But we shall see.


Yeah the central and southern end of the island have been getting a bit more rain and some gusty winds. Extreme S FL is about to get some heavy rain in a couple of hours
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that aint happening unless the ATL stabilizes and moistens up, its a desert out there with the SAL
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Bonnie!! your a sad excuse for a tropical cyclone!! Now drop and give me 20!!
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Quoting atmosweather:


Morning Baha! Glad to hear the effects weren't too bad...the storm is clipping along at a quick pace.
Morning atmo. I have a feeling they got somewhat more rain in Exuma and South Andros than we did here. However, I'm very glad it wasn't any worse. This was a best case scenario for us.

With Bonnie fleeing the scene, my biggest concern right now is that this track or one similar to it will happen with a much larger more powerful system in a few weeks. It often happens once the synoptic pattern gets "set".

But we shall see.
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Quoting BahaHurican:
All I'm going to say about Bonnie is don't be underwhelmed by the qualities of this storm. I'm expecting to see Bonnie enter the GoM by this time tomorrow afternoon at the rate she is going, but unless conditions are extremely conducive, I don't see huge developments.

I think I'll go back to bed in a couple minutes. This felt a lot more than a fall frontal passage than a tropical storm, I have to tell you....


Lol. Edouard was like that for us. Especially weird because we were thinking Oh no! Not another Humberto! Didn't even lose electricity. :)
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Seems like I may have pulled an all nighter for a weak tropical storm. Whatever. Just good to know that I could do it and am ready for a possible bigger threat down the road.
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Quoting BahaHurican:
Morning everybody. I posted the following in the last blog before I realized we'd gotten an update...

2818. BahaHurican 3:59 AM EDT on July 23, 2010
Morning all. Just woke up to the sound of rainfall, tropical from Bonnie. Amazing to see that most of the shower activity is practically past us already.


I took a look outside since then, and I don't think we got as much rain as I expected. The groud looks pretty dry out there, which means the rainfall hasn't been torrential. The wind is still blowing pretty steadily at about 15 - 20 mph, though from the SE now, indicative of the passage of Bonnie.


Morning BAHA. Glad it didnt get real bad. I think she is moving fast.
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All I'm going to say about Bonnie is don't be underwhelmed by the qualities of this storm. I'm expecting to see Bonnie enter the GoM by this time tomorrow afternoon at the rate she is going, but unless conditions are extremely conducive, I don't see huge developments.

I think I'll go back to bed in a couple minutes. This felt a lot more than a fall frontal passage than a tropical storm, I have to tell you....
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Quoting atmosweather:


Lol no problem :) I say you're doing fine!

IR loop is a perfect illustration of how the mid level energy is still getting tugged NNW-ward by the S-erly shear and the influence of the ULL...while the LLC continues to move WNW or NW-ward away from it. The circulation is becoming extremely elongated.


Yep she looks like she's being stretched to her limits. If nothing else this has been educational. Like the Pacific typhoon type that took forever to get going.
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Quoting BahaHurican:
Morning everybody. I posted the following in the last blog before I realized we'd gotten an update...

2818. BahaHurican 3:59 AM EDT on July 23, 2010
Morning all. Just woke up to the sound of rainfall, tropical from Bonnie. Amazing to see that most of the shower activity is practically past us already.


I took a look outside since then, and I don't think we got as much rain as I expected. The groud looks pretty dry out there, which means the rainfall hasn't been torrential. The wind is still blowing pretty steadily at about 15 - 20 mph, though from the SE now, indicative of the passage of Bonnie.


Morning Baha! Glad to hear the effects weren't too bad...the storm is clipping along at a quick pace.
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Morning everybody. I posted the following in the last blog before I realized we'd gotten an update...

2818. BahaHurican 3:59 AM EDT on July 23, 2010
Morning all. Just woke up to the sound of rainfall, tropical from Bonnie. Amazing to see that most of the shower activity is practically past us already.


I took a look outside since then, and I don't think we got as much rain as I expected. The groud looks pretty dry out there, which means the rainfall hasn't been torrential. The wind is still blowing pretty steadily at about 15 - 20 mph, though from the SE now, indicative of the passage of Bonnie.
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Quoting KoritheMan:


I'm thinking that they will terminate advisories at the 11AM advisory, after morning visibles become available.


They most likely won't just because it's so close to the shoreline and it would be pointless and strange to the public since all of the effects are to the N of the center and will impact S FL anyway.
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Quoting homelesswanderer:


Oh ok. Thanks again. :) I'll get there one of these days. Lol.


Lol no problem :) I say you're doing fine!

IR loop is a perfect illustration of how the mid level energy is still getting tugged NNW-ward by the S-erly shear and the influence of the ULL...while the LLC continues to move WNW or NW-ward away from it. The circulation is becoming extremely elongated.
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Quoting atmosweather:


Well the 5am advisory will be out in a little bit...I would doubt they downgrade the winds because even though she could no longer technically be a tropical cyclone they are still just barely finding enough 35 kt winds in the bands to the NE.


I'm thinking that they will terminate advisories at the 11AM advisory, after morning visibles become available.
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Waiting for the 5AM Advisory and then probably getting some sleep before the 8AM. lol I managed to pull off an all nighter.
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Quoting atmosweather:


Not yet...the SE ridge is still holding strong and will continue to do so for at least 2-3 days.


Oh ok. Thanks again. :) I'll get there one of these days. Lol.
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Quoting Hurricaneins:
8a advisory will still have it as a TS?


Well the 5am advisory will be out in a little bit...I would doubt they downgrade the winds because even though she could no longer technically be a tropical cyclone they are still just barely finding enough 35 kt winds in the bands to the NE.
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Quoting homelesswanderer:


Night. I don't know a lot about steering layers. But that looks quite different from 3hrs ago. At least the ridge over the SE doesn't have a spiral thing anymore like the ridge in the Atlantic. Does that mean the SE ridge is weakening?


Not yet...the SE ridge is still holding strong and will continue to do so for at least 2-3 days.
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8a advisory will still have it as a TS?
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RECON going through the SW side and still not finding any winds with westerly components. This LLC is very close to being open, there should be at least a couple of reported NW-erly or W-erly winds.
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Since last fix, Bonnie has been traveling on a heading of 305 (slightly more north) at a speed of about 21 mph.
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Quoting btwntx08:
very tired good night


Night. I don't know a lot about steering layers. But that looks quite different from 3hrs ago. At least the ridge over the SE doesn't have a spiral thing anymore like the ridge in the Atlantic. Does that mean the SE ridge is weakening?
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Quoting homelesswanderer:


OH OK. I didn't know that. See I'm a little smarter now. Thank you. :)


Lol you're welcome :)
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This position is 30 miles to the SE of the NHC's current 8AM forecast point...6 hr movement is around 310/13 kts. So the NHC are almost dead on with that point, maybe 15-20 miles too far SE because of the slightly increased forward speed.
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Quoting atmosweather:
Yep...24.1N 78.3W is in fact the center.

000
URNT12 KNHC 230803
VORTEX DATA MESSAGE AL032010
A. 23/07:37:00Z
B. 24 deg 06 min N
078 deg 20 min W
C. 850 mb 1497 m
D. 34 kt
E. 057 deg 59 nm
F. 128 deg 41 kt
G. 056 deg 67 nm
H. 1009 mb
I. 18 C / 1526 m
J. 19 C / 1530 m
K. 18 C / NA
L. NA
M. NA
N. 134 / 8
O. 0.02 / 0 nm
P. AF305 0403A BONNIE OB 10
MAX FL WIND 41 KT NE QUAD 07:15:50Z
MAX FL TEMP 19 C 081 / 6 NM FROM FL CNTR


1009 ... pressure is holding, for now
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Quoting atmosweather:
Yep...24.1N 78.3W is in fact the center.

000
URNT12 KNHC 230803
VORTEX DATA MESSAGE AL032010
A. 23/07:37:00Z
B. 24 deg 06 min N
078 deg 20 min W
C. 850 mb 1497 m
D. 34 kt
E. 057 deg 59 nm
F. 128 deg 41 kt
G. 056 deg 67 nm
H. 1009 mb
I. 18 C / 1526 m
J. 19 C / 1530 m
K. 18 C / NA
L. NA
M. NA
N. 134 / 8
O. 0.02 / 0 nm
P. AF305 0403A BONNIE OB 10
MAX FL WIND 41 KT NE QUAD 07:15:50Z
MAX FL TEMP 19 C 081 / 6 NM FROM FL CNTR


Barely a tropical storm.
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Quoting cchsweatherman:
Just been spending time reviewing satellite imagery and the Hurricane Hunter data. Definitely becoming less organized as the night progresses and struggling to maintain tropical storm status right now as the center has become much less defined and the system becomes stretched in a SE to NW orientation.


Yeah, lower level convergence is just a big long smear. Bonnie has some work to do to retain the TC label.
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Yep...24.1N 78.3W is in fact the center.

000
URNT12 KNHC 230803
VORTEX DATA MESSAGE AL032010
A. 23/07:37:00Z
B. 24 deg 06 min N
078 deg 20 min W
C. 850 mb 1497 m
D. 34 kt
E. 057 deg 59 nm
F. 128 deg 41 kt
G. 056 deg 67 nm
H. 1009 mb
I. 18 C / 1526 m
J. 19 C / 1530 m
K. 18 C / NA
L. NA
M. NA
N. 134 / 8
O. 0.02 / 0 nm
P. AF305 0403A BONNIE OB 10
MAX FL WIND 41 KT NE QUAD 07:15:50Z
MAX FL TEMP 19 C 081 / 6 NM FROM FL CNTR
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Quoting atmosweather:


You can see a shortwave trough digging into the NW that is supposed to push a front across the central Plains...but it is likely to stall out before reaching the MS/TN valley and the trough will lift out NE-ward. This should act to erode a small W-ern portion of the ridge which could turn Bonnie/whatever is left NW or NNW-ward as it approaches the Gulf coast.


OH OK. I didn't know that. See I'm a little smarter now. Thank you. :)
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Quoting Hardcoreweather2010:
What's up with all this talk about it being an open wave and weakening ?



The system's low level center is still exposed and well away from the deep convection which is where the mid level energy lies...and the strong easterly low level winds are pushing the LLC even further from the mid level spin. This means the storm is extremely disorganized and is fully decoupled because it cannot align itself vertically, which prevents convection from develop over the LLC. Conditions remain average at best so unless the LLC can reform under some of the convection Bonnie could easily degenerate into an open wave.
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06z wind products are out from CIMSS. 850, 700, 500 are stacked.

It looks like the convection is going to pick up speed to the W or WSW before the (putative) lower level circulation. It still looks to me like it may reconnect with the LLC.

06z steering

06z vort, winds, etc
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Quoting cchsweatherman:
Just been spending time reviewing satellite imagery and the Hurricane Hunter data. Definitely becoming less organized as the night progresses and struggling to maintain tropical storm status right now as the center has become much less defined and the system becomes stretched in a SE to NW orientation.


Thanks...

v/r

Jon
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562. xcool
poof
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What's up with all this talk about it being an open wave and weakening ?

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Just been spending time reviewing satellite imagery and the Hurricane Hunter data. Definitely becoming less organized as the night progresses and struggling to maintain tropical storm status right now as the center has become much less defined and the system becomes stretched in a SE to NW orientation.
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Quoting homelesswanderer:
What was supposed to weaken the ridge? I see a trough stretching down to west Tx. I haven't looked at those. Been following the fronts that have stalled. Thought they were going to break it down. So I got a lot to learn. :)


You can see a shortwave trough digging into the NW that is supposed to push a front across the central Plains...but it is likely to stall out before reaching the MS/TN valley and the trough will lift out NE-ward. This should act to erode a small W-ern portion of the ridge which could turn Bonnie/whatever is left NW or NNW-ward as it approaches the Gulf coast.
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558. xcool
hmm
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Quoting Skyepony:
Agreed on the center fix..with such a fleeting west wind & not at all stacked with the lowest pressure wunder if we'll even get a vortex message..


It hasn't looked closed for about 6 hours now...I don't think this is even a tropical cyclone but regardless the NHC would never post that to the public just hours away from "landfall".
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What was supposed to weaken the ridge? I see a trough stretching down to west Tx. I haven't looked at those. Been following the fronts that have stalled. Thought they were going to break it down. So I got a lot to learn. :)
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553. xcool
she move move wnw .
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551. Skyepony (Mod)
Agreed on the center fix..with such a fleeting west wind & not at all stacked with the lowest pressure wunder if we'll even get a vortex message..
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550. xcool
1007.now
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Center looks to be near 24.1N 78.3W according to RECON...pressure has not fallen. Only a couple of westerly wind components. Let's see what the vortex shows.
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547. xcool
lol
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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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