Bonnie weakens to a tropical depression
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
Reader Comments
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Talking about the Oil...
I find it amazing that the oil has remained virtually where it has been all along.
I would have thought that the currents would have long dispersed it further afield. I was not aware that the GOM in that area is so static, for so long.
Strange to me.........
Bingo :) Give the man a cookie :)
Yup, Rita 2005 was one of the most beautiful cases of such a setup. Upper-level low backing away over Cuba ventilated the tropical wave to the east and allowed Rita to develop east of the Bahamas.
Upper winds 0z September 18th, 2005, the time of Rita's first advisory as a tropical depression: Notice the upper low to the WSW over Cuba.
24 hours later.....wow just classic: Backing away SW ventilating Rita as upper ridging develops over the cyclone.
Another 24 hours later on the 20th the upper low south of Cuba was beginning to dissipate due to heat being released into the upper atmosphere, and Rita was nearing hurricane status.
Rita was a very classic case of the upper low being very much responsible for her formation, ventilating the tropical wave as it backs away and providing a favorable pocket to develop in. You won't wind a more classic case than this. That's why trough-splits in the tropics are favorable if the position of a disturbance relative them is right. Always watch to the east of upper lows retrograding away westward in the tropics.
ok, cool thanks!
What is the difference in a wave and a low pressure system? Is a wave identified as being over water and a lps identified as being over land?
Thanks
Dan
I would have thought the oil would have been to Europe by now
Better good or better bad? I studied the loop and my uneducated eye can't tell. Sorry
Have you seen ROFFS?
http://roffs.com/deepwaterhorizon.html
Will be around sometime in the a.m., but dunno how much time I'll actually spend in here tomorrow. Gotta get stuff ready for next week... :o(
...or at least the Bahamas....................
The NHC has to answer questions from big folks that have a heightened interest along the gulf coast. Why go to the meeting with old data? Just being professional and ready to answer questions and/or provide data to other involved parties..
But I would have to guess that without that , uh, area of heightened interest, they probably would have stayed home!
Yes exactly. That has to be the only reason. There's no evidence to support a TC designation still.
I don't think they are going to know just how bad it is for quite sometime.
They ummm dispersed it (out of sight, out of mind)
Look at the pictures of the spill in China... which is what... 1/1000 of the GOM, or even less. You guys have all of that.. somewhere under the surface. I believe the term is FUBAR.
WTNT33 KNHC 240234
TCPAT3
BULLETIN
TROPICAL DEPRESSION BONNIE ADVISORY NUMBER 7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032010
1100 PM EDT FRI JUL 23 2010
...DISORGANIZED BONNIE MOVING THROUGH THE EASTERN GULF OF MEXICO...
SUMMARY OF 1100 PM EDT...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...26.4N 83.4W
ABOUT 395 MI...635 KM ESE OF THE MOUTH OF THE MISSISSIPPI RIVER
ABOUT 85 MI...135 KM SW OF SARASOTA FLORIDA
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/HR
PRESENT MOVEMENT...WNW OR 295 DEGREES AT 17 MPH...28 KM/HR
MINIMUM CENTRAL PRESSURE...1010 MB...29.83 INCHES
WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...
NONE.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* DESTIN FLORIDA TO MORGAN CITY LOUISIANA...INCLUDING LAKE
PONTCHARTRAIN
FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED
STATES...INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE
MONITOR PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE
FORECAST OFFICE.
DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 1100 PM EDT...0300 UTC...THE CENTER OF TROPICAL DEPRESSION BONNIE
WAS LOCATED NEAR LATITUDE 26.4 NORTH...LONGITUDE 83.4 WEST. THE
DEPRESSION IS MOVING TOWARD THE WEST-NORTHWEST NEAR 17 MPH...
28 KM/HR. THIS GENERAL TRACK WITH A DECREASE IN FORWARD SPEED IS
EXPECTED TO CONTINUE DURING THE NEXT TWO DAYS. ON THE FORECAST
TRACK...BONNIE IS EXPECTED TO CROSS THE EASTERN GULF OF MEXICO
TONIGHT AND SATURDAY AND REACH THE NORTHERN GULF COAST SATURDAY
NIGHT OR EARLY SUNDAY.
MAXIMUM SUSTAINED WINDS ARE NEAR 35 MPH...55 KM/HR...WITH HIGHER
GUSTS. SLIGHT STRENGTHENING IS FORECAST ON SATURDAY...AND BONNIE
COULD REGAIN TROPICAL STORM STRENGTH BEFORE REACHING THE NORTHERN
GULF COAST.
THE LATEST MINIMUM CENTRAL PRESSURE REPORTED BY AN AIR FORCE RESERVE
HURRICANE HUNTER AIRCRAFT IS 1010 MB...29.83 INCHES.
HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM FORCE WINDS MAINLY IN SQUALLS WILL LIKELY
BEGIN ALONG PORTIONS OF THE NORTHERN GULF COAST WITHIN THE WARNING
AREA ON SATURDAY.
RAINFALL...BONNIE IS EXPECTED TO PRODUCE TOTAL RAINFALL
ACCUMULATIONS OF 1 TO 3 INCHES OVER PORTIONS OF SOUTHEASTERN
LOUISIANA...SOUTHERN ALABAMA...SOUTHERN MISSISSIPPI...AND THE FAR
WESTERN FLORIDA PANHANDLE...WITH POSSIBLE ISOLATED MAXIMUM AMOUNTS
OF 5 INCHES.
STORM SURGE...STORM SURGE WILL RAISE WATER LEVELS BY AS MUCH AS 2 TO
4 FEET ABOVE GROUND LEVEL ALONG THE IMMEDIATE COAST NEAR AND TO THE
RIGHT OF WHERE THE CENTER MAKES LANDFALL ON THE NORTHERN GULF
COAST.
NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...200 AM EDT.
NEXT COMPLETE ADVISORY...500 AM EDT.
$$
FORECASTER BEVEN
Usually talking about a tropical wave being open (no circulation), and a tropical low being a closed circulation. Both being over water.
Hurricane Isabel (2003) as seen from orbit during Expedition 7 of the International Space Station.
The eye, eyewall and surrounding rainbands that are characteristics of tropical cyclones are clearly visible in this view from space.
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain.
Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easters, European windstorms, and polar lows, leading to their classification as "warm core" storm systems.
The term "tropical" refers to both the geographic origin (as in originating between the Tropic of Cancer and the Tropic of Capricorn) of these systems, which form almost exclusively in tropical regions of the globe, and their formation in maritime tropical air masses. The term "cyclone" refers to such storms' cyclonic nature, with counterclockwise rotation in the Northern Hemisphere and clockwise rotation in the Southern Hemisphere.
Depending on its location and strength, a tropical cyclone is referred to by names such as hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone.
While tropical cyclones can produce extremely powerful winds and torrential rain, they are also able to produce high waves and damaging storm surge as well as spawning tornadoes. They develop over large bodies of warm water, and lose their strength if they move over land.
This is why coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from receiving strong winds. Heavy rains, however, can produce significant flooding inland, and storm surges can produce extensive coastal flooding up to 40 kilometres (25 mi) from the coastline.
Although their effects on human populations can be devastating, tropical cyclones can also relieve drought conditions. They also carry heat and energy away from the tropics and transport it toward temperate latitudes, which makes them an important part of the global atmospheric circulation mechanism.
As a result, tropical cyclones help to maintain equilibrium in the Earth's troposphere, and to maintain a relatively stable and warm temperature worldwide.
Many tropical cyclones develop when the atmospheric conditions around a weak disturbance in the atmosphere are favorable.
The background environment is modulated by climatological cycles and patterns such as the Madden-Julian oscillation, El Niño-Southern Oscillation, and the Atlantic multidecadal oscillation.
Others form when other types of cyclones acquire tropical characteristics. Tropical systems are then moved by steering winds in the troposphere; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop an eye.
On the other end of the spectrum, if the conditions around the system deteriorate or the tropical cyclone makes landfall, the system weakens and eventually dissipates. It is not possible to artificially induce the dissipation of these systems with current technology.
Good point....I guess they would be hard pressed because of the oil situation.
LOL ... sometimes the NHC's got the toughest job in the world.
To say Bonnie is struggling is being very kind to this diminutive "tropical cyclone".
Mo stuff in the Cauldron eh ?
Yes, Pat. More's brewin, but that's no surprise.
We'll know something's up if it gets KmanIslander's attention.
The oil's one thing, the 2 million gallons of Corexit is quite another. There's already circumstantial proof that is getting carried inland and dropping as acid rain all over the south/southeast, midwest and even through the northeast. 2-butoxyethanol is the primary poison involved and I shudder to think what will happen as more storms continue to push inland.
Yeah I have, and have been looking at that from time to time...
Shows plenty of water-movement via. currents, wind, temps etc etc.
And yet, the oil stays put (generally speaking)
Later
WTNT43 KNHC 240235
TCDAT3
TROPICAL DEPRESSION BONNIE DISCUSSION NUMBER 7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032010
1100 PM EDT FRI JUL 23 2010
BONNIE IS CURRENTLY COMPRISED OF A CONVECTIONLESS SWIRL OF LOW
CLOUDS EMBEDDED IN A LARGER-SCALE LOW-LEVEL TROUGH. AN AIR FORCE
RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING THE SYSTEM HAS
FOUND WINDS NEAR TROPICAL-STORM FORCE NORTH OF THE CENTER...BUT IS
HAVING A HARD TIME FINDING WESTERLY WINDS ON THE SOUTH SIDE. THE
AIRCRAFT DATA DOES SHOW A CLOSED LOW PRESSURE AREA WITH A CENTRAL
PRESSURE OF 1010 MB. BASED ON THIS CONFLICTING INFORMATION...
BONNIE REMAINS A 30 KT DEPRESSION AT THIS TIME.
THE CYCLONE HAS TURNED A LITTLE TO THE LEFT DURING THE PAST SEVERAL
HOURS...WITH THE INITIAL MOTION NOW 295/15. BONNIE REMAINS ON THE
SOUTH SIDE OF A DEEP-LAYER RIDGE OVER THE SOUTHEASTERN UNITED
STATES AND EAST OF A LARGE MID/UPPER-LEVEL LOW CENTERED OVER THE
WEST CENTRAL GULF OF MEXICO. THIS COMBINATION IS FORECAST TO STEER
THE STORM TO A LANDFALL ALONG THE NORTHERN GULF COAST. ALL THE
TRACK GUIDANCE AGREES WITH THIS SCENARIO...WITH THE MODELS
CLUSTERED OVER THE SOUTHEAST LOUISIANA AND SOUTHERN MISSISSIPPI
COASTS. AFTER LANDFALL...BONNIE OR ITS REMNANT LOW SHOULD TURN
NORTHWARD AT A SLOWER FORWARD SPEED AROUND THE WESTERN END OF THE
RIDGE. THE NEW FORECAST TRACK IS SHIFTED TO THE LEFT BASED UPON
THE CURRENT POSITION AND MOTION...AND LIES JUST TO THE RIGHT OF THE
CENTER OF THE GUIDANCE ENVELOPE.
BONNIE REMAINS IN A LESS THAN IDEAL ENVIRONMENT OF STRONG
SOUTHEASTERLY VERTICAL WIND SHEAR...CONFLUENT UPPER-LEVEL FLOW...
AND UPPER-LEVEL DRY AIR ENCROACHING ON THE CYCLONE. MOST OF THE
INTENSITY GUIDANCE RESPONDS TO THIS BY SHOWING WEAKENING OR
DISSIPATION BEFORE LANDFALL...WITH ONLY THE SHIPS AND LGEM SHOWING
ANY INTENSIFICATION. THE INTENSITY FORECAST IS BASED ON THE
PREMISE THAT ENOUGH CONVECTION WILL RE-DEVELOP TO CAUSE SLIGHT
STRENGTHENING BEFORE BONNIE REACHES THE NORTHERN GULF COAST. AN
INCREASINGLY LIKELY ALTERNATIVE SCENARIO IS THAT THE CYCLONE WILL
DECAY TO A REMNANT LOW OR OPEN TROUGH SOMETIME ON SATURDAY DUE TO A
LACK OF CONVECTION.
FORECAST POSITIONS AND MAX WINDS
INITIAL 24/0300Z 26.4N 83.4W 30 KT
12HR VT 24/1200Z 27.7N 85.7W 30 KT
24HR VT 25/0000Z 29.2N 88.5W 35 KT
36HR VT 25/1200Z 30.5N 90.5W 35 KT...INLAND
48HR VT 26/0000Z 31.4N 91.8W 25 KT...INLAND
72HR VT 27/0000Z 34.0N 93.0W 20 KT...POST-TROP/REMNT LOW
96HR VT 28/0000Z...DISSIPATED
$$
FORECASTER BEVEN
He must have a trial...or is traveling.
I miss his input.
You too, Pat & everybody.
Peace.
You see, that's the problem they have being both a scientific organization and an important public agency...they have to be aware of safety/well-being as well as meteorological standards.
Lots of low pressure areas cross the continent every year, and I am unsure of what the ones that develop a closed center of rotation are called.
Back after some book learning.
Dan
The NHC mission statement is to save lives, mitigate property loss, and improve economic efficiency by issuing the best watches, warnings, forecasts and analyses of hazardous tropical weather, and by increasing understanding of these hazards.
It is important for you to pay attention when you hear alerts, watches, and warnings provided by this official hurricane organization.
By listening to information given and the official National Hurricane Center concern behind it, you will be able to make education decisions on preparing for a hurricane, preventative damage, and protecting your family.
At this point they're likely maintaining continuity until they are 100% certain Bonnie is no longer a tropical cyclone.
This tells the wholwe story.
So true. A hot potato. More than just pure meteorolgy going on. Gotta look like you're "on the job"!
AIRCRAFT DATA DOES SHOW A CLOSED LOW PRESSURE AREA WITH A CENTRAL
PRESSURE OF 1010 MB.
What aircraft data? Did we miss something? The last W-erly wind found in the entire southern envelope was 3 hours ago.
Looks like they shifted the track back alittle to the west. Is that correct?
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