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 Tazmanian:
the HH is up


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would some one like too tell me why they did not upgrade TD 2 with this info

Mission
Number Agency Time Lowest Extrapolated
Surface Pressure Highest
Flt. Lvl. Wind (30s Avg.) Highest SFMR Peak
(10s Avg.) Sfc. Wind Map
01 Air Force 07/08 15:20:00Z 1004.1mb (~29.65 inHg) 41kts (~47.1mph) 44kts (~50.6mph)
[Google Earth] [Google Maps]

Non-Tasked Messages For This Storm

Mission Agency Time Lowest Extrapolated
Surface Pressure Highest
Flt. Lvl. Wind (30s Avg.) Highest SFMR Peak
(10s Avg.) Sfc. Wind Map
WX NOAA 07/08 03:45:30Z 987.3mb (~29.15 inHg) 35kts (~40.2mph) 34kts (~39.1mph)
[Google Earth] [Google Maps]
WX NOAA 07/07 23:55:30Z 1001.1mb (~29.56 inHg) 44kts (~50.6mph) 39kts (~44.8mph)
[Google Earth] [Google Maps]
WX NOAA 07/07 15:52:00Z 987.0mb (~29.15 inHg) 39kts (~44.8mph) 43kts (~49.4mph)
[Google Earth] [Google Maps]
WX NOAA 07/06 23:50:00Z 1000.5mb (~29.54 inHg) 31kts (~35.6mph) 21kts (~24.1mph)
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Quoting jasoniscoolman2010x:
something spining north of Puerto Rico
back away from the keyboard
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258. OSMS
Visting this blog after a few years. Use to be a great resource for Katrinia and pre Katrinia.

Seems to have turned into a can you top me now.

Any links that are more concrned with forecasting instead of I win based on storm or no storm are appreciated.
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Quoting fallinstorms:


don't matter

the wind is too rough

and the sea is dry

they need more then heat



The sea is dry? Now I've heard everything lol.


Trade winds still below normal:

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Quoting atmosweather:


Finally what was left of the deep convection is waning...I'm surprised it has held on this long. Looks like a degenerating system...and there's really no feasible way it can redevelop because of it's forward speed and the fact that the energy is completely separated from the LLC.

We are getting a bad storm now in the panhandle (Gulf Breeze/pens bch)you getting any of this Ike??
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Quoting Levi32:


Lol, only 1 named storm by the end of July (well 2009 only had a TD)

LOL 2010 had both a TD AND a TS in July.
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ok seriously...I'm done
Member Since: November 1, 2004 Posts: 25 Comments: 8912
Quoting StormW:
189 & 190 correct.

How many storms in each one?


2002 had 12 named storms, 2004 had 15 named storms, and 2009 had 9 named storms, depressions or how many became huriicanes not listed, 2002 and 2004 were above average in named storms and 2009 was basically just 1-2 below average in terms of named systems and they were EL NINO years ,yes StormW I see what you're getting at, this has about 60-80% chance to above the Season average in named storms considering we are in La Nina now!
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Quoting atmoaggie:
I dunno. July's MSLP isn't always a good indicator of Aug, Sept, Oct.


Would have to disagree there, at least with what I am seeing.

Let's look at some of our top analog years, 1964, 1998, and 2005:

July MSLP Anomalies for 1964, 1998, and 2005:



Now look at the heart of the hurricane season:

August-September-October MSLP Anomalies for 1964, 1998, and 2005:



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Hello Colin. This is Bonnie. I am not feeling well tonight and need to cancel our meeting. I have come down with the ULL Flu. Catch up with me later....
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Quoting Levi32:


I think the parallel being drawn here is that with a La Nina the odds of seeing above-average numbers are high, considering that most El Nino years during a warm AMO will still produce near-average seasons.


And also the fact that June and July mean virtually nothing to the overall activity for an entire hurricane season.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
the HH is up
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245. redUK
I guess the high peaks of Florida killed Bonnie for good.

Can anyone name an analog year to this one, where July was dominated by SE ridging and where ULLs roamed the tropics.

(or are most July's like this)?

Thanks!
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and the sea is dry

Moses?
Member Since: November 1, 2004 Posts: 25 Comments: 8912
Quoting IKE:


Finally what was left of the deep convection is waning...I'm surprised it has held on this long. Looks like a degenerating system...and there's really no feasible way it can redevelop because of it's forward speed and the fact that the energy is completely separated from the LLC.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
241. xcool
100% RIP BONNIE
Member Since: September 26, 2009 Posts: 2 Comments: 15603
Quoting Levi32:


Lol, only 1 named storm by the end of July (well 2009 only had a TD)


Well Storm said I was right. :p Don't know what to yet. Lol. Must read back. :)
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Quoting IKE:


I hear Bender giggling in the background...
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New Orleans, Louisiana (Airport)
Updated: 10 min 42 sec ago
93 °F
Mostly Cloudy
Humidity: 50%
Dew Point: 72 °F
Wind: 5 mph from the East

Wind Gust: 16 mph
Pressure: 30.04 in (Falling)
Heat Index: 101 °F

I would take some of those clouds and breeze from TD3 about now...
Member Since: November 1, 2004 Posts: 25 Comments: 8912
233. xcool
POOF SHE GOOGO BYEEE
Member Since: September 26, 2009 Posts: 2 Comments: 15603
Quoting atmosweather:


12, 15, 9.


I think the parallel being drawn here is that with a La Nina the odds of seeing above-average numbers are high, considering that most El Nino years during a warm AMO will still produce near-average seasons.
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Quoting Levi32:
And, again, does this look like an inactive season ahead?

July MSLP anomalies thus far (through the 20th):

I dunno. July's MSLP isn't always a good indicator of Aug, Sept, Oct.
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would some one tell the nhc too kill this storm
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Quoting 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....

$$





LOL!
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Quoting Levi32:


That wouldn't prevent a storm or two from popping up either. It would be really hard to reverse the current worldwide overturning circulation to put the dominant upward motion over the Pacific and downward motion over the Atlantic. SST anomalies do not support that.


That's the key point here...a downward MJO phase does not eliminate tropical cyclone development...it just adds a negative environmental factor for development. If a system with a strong surface reflection gets in the right area it will still develop.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
And, again, does this look like an inactive season ahead?

July MSLP anomalies thus far (through the 20th):

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Quoting Tazmanian:



i think this guy sould be dr m back up when dr m go a way for 2 weeks



re post
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223. IKE
Member Since: June 9, 2005 Posts: 23 Comments: 37858
I found this...Link

A TUTT LOW NORTH OF HISPANIOLA AND PUERTO RICO IS DRIVEN BY A
SUBTROPICAL RIDGE THAT EXTENDS OVER THE WESTERN ATLANTIC TO THE
NORTH OF 30N. THROUGH 36 HRS THE TUTT WILL RETROGRESS ACROSS THE
SOUTHEAST/ CENTRAL BAHAMAS. AT 500 HPA THE MODELS ALSO SHOW A
SHORT WAVE RIDGE BUILDING IN FROM THE NORTH...WITH PRECIPITABLE
WATER CONTENT IN THE COLUMN RAPIDLY DROPPING BELOW 35MM BY 60-72
HRS. AS THE RIDGE IS TO THEN MEANDER OVER THE NORTHEAST
CARIBBEAN... SHORT WAVE VORTICES WILL THEN EJECT TO THE SOUTHEAST
ACROSS THE FRENCH ISLANDS INTO THE SOUTHEAST CARIBBEAN...AND FOR
THE MOST PART THE MODELS KEEP THEM AWAY FROM HISPANIOLA... PUERTO
RICO AND VIRGIN ISLES.

IN THE SHORT RANGE...THE TUTT ALOFT WILL VENT DIURNAL CONVECTION
ACROSS THE NORTHEAST CARIBBEAN. ON DAY 02 MODELS SHOW A
PROGRESSIVE PERTURBATION IN THE LOW LEVEL EASTERLIES EJECTING
ACROSS THE BASIN. A DRYING TREND IS THEN EXPECTED BETWEEN 24-48
HRS AS THE MID LEVEL RIDGE STRENGTHENS THE SUBSIDENCE CAP. IN THE
MEDIUM RANGE... THE MODELS SHOW SHOWERS RETURNING TO THE NORTHEAST
CARIBBEAN BY TUESDAY-WEDNESDAY AS SHALLOW MOISTURE IN THE TRADE
WIND EASTERLIES ENTER THE BASIN. THE MODELS FAVOR LIGHT TO
MODERATE RAINFALL AMOUNTS DURING THAT PERIOD... AND THAT SEEMS TO
BE CONSISTENT WITH FORECAST OF UNFAVORABLE MJO CONDITIONS ACROSS
THE CARIBBEAN BASIN. THE CLIMATOLOGICAL MODELS CONTINUE TO DIVERGE
ON HOW LONG THE UNFAVORABLE CONDITIONS ARE GOING TO LAST...WITH
THE EWP AND GFS SHOWING A STRONG SUBSIDENT PATTERN ESTABLISHING
INTO THE MIDDLE OF AUGUST. THE CFS CONTINUES TO SHOW WEAK
SUBSIDENCE TO NEUTRAL CONDITIONS...WITH BRIEF PERIODS OF
DIVERGENCE ALOFT TO PUT A DENT ON THE PATTERN.

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Quoting StormW:
189 & 190 correct.

How many storms in each one?



12, 15, 9.
Member Since: September 24, 2005 Posts: 33 Comments: 9265
219. xcool
Tazmanian NO
Member Since: September 26, 2009 Posts: 2 Comments: 15603
Quoting atmosweather:


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.


That wouldn't prevent a storm or two from popping up either. It would be really hard to reverse the current worldwide overturning circulation to put the dominant upward motion over the Pacific and downward motion over the Atlantic. SST anomalies do not support that.
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Radar shot of where the possible tornado was in Pensacola FL

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Quoting fallinstorms:


i think it will be really long and strong

MJO is what will makes this year so weak


This new handle of yours makes how many? 10? 15? More?
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Quoting xcool:


I HOPEING PEOPLE CANN SEE THIS OR I DELETE ITTT.


x cool did you see my last commets
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ok...I'm done
Member Since: November 1, 2004 Posts: 25 Comments: 8912
212. xcool


I HOPEING PEOPLE CANN SEE THIS OR I DELETE ITTT.
Member Since: September 26, 2009 Posts: 2 Comments: 15603
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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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.