Unanswered questions concerning Hurricane Isaac

By: Dr. Jeff Masters , 4:35 PM GMT on August 31, 2012

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The top winds of Tropical Depression Isaac have fallen to 25 mph, but the storm continues to be a potent rain-maker as it heads north-northwest at 11 mph into Missouri. Isaac has spawned up to 20 suspected tornadoes, brought storm surges as high as 13.6' to the coast (in Lake Borgne, LA), and dumped 20" of rain at one station in New Orleans. The 13.27" of rain that fell at Hattiesburg, MS broke the record for wettest August in the city's history (previous record: 13.03" in 1987.) Major flooding is occurring on seven rivers in Louisiana and Mississippi. Isaac is being blamed for at least four deaths in the U.S., 24 in Haiti, and five in the Dominican Republic.

A few notable rainfall totals from Isaac, through 11 am EDT on Friday:

20.08" New Orleans, LA
15.02" Marion, MS
13.99" Pascagoula, MS
13.27" Hattiesburg, MS
10.85" Gulfport, MS
10.39" Slidell, LA
10.17" Biloxi, MS
9.85" Mobile, AL
7.38" Pine Bluff, AR
5.95" Baton Rouge, LA

A major reason for Isaac's heavy rainfall totals has been its very slow motion. This slow speed was due to the fact Isaac has been bumping into a ridge of high pressure that is unusually strong, due to the intense drought over the center of the U.S.; strong drought-amplified high pressure areas are very resistant to allowing any low pressure areas to intrude into their domain. The high pressure area was strong enough this week to allow several all-time records for heat this late in the year to be set:

112° on August 29 at Winner, SD
108° on August 29 at Valentine, NE
107° on August 29 at Corpus Christi, TX
97° on August 29 at Denver, CO (2nd highest so late in the year)


Figure 1. Nighttime view of Hurricane Isaac taken at 1:57 am CDT August 29, 2012, by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi-NPP satellite. The VIIRS day-night band detects light in a range of wavelengths from green to near-infrared, and uses light intensification to enable the detection of dim signals. In this case, the clouds of Isaac were lit by moonlight. Image credit: NASA.

Isaac's beneficial rains falling in drought-stricken regions
Hurricanes get a lot of attention because of the billions in damage they cost, and the lives they disrupt. AIR Worldwide estimated today that insured damage from Isaac would cost up to $2 billion. This does not include damage to infrastructure or uninsured damage, so the final price tag of Isaac's rampage will be more like $3 - $5 billion. However, Isaac is now dumping beneficial rains over Arkansas, Missouri, Illinois, Indiana, Ohio, and Kentucky--regions stricken by the worst drought since the 1950s or 1930s, depending upon the exact location. These regions need 9 - 18 inches of rain to pull them out of drought. Isaac's 3 - 6 inches of rain will not end the drought, but will put a pretty good dent in it. I expect that 3 - 6 inches of rain for a wide swath of prime agricultural land in extreme drought is probably worth at least $5 billion, when you consider that a recent estimate by a Purdue economist put the cost of the great drought of 2012 at more than $77 billion. Only Hurricane Katrina ($146 billion) and the drought of 1988 ($78 billion) have been more expensive disasters, according to NOAA's National Climatic Data Center. Unfortunately, Isaac's arrival is poorly timed, as the storm is arriving during harvest season. The strong winds associated with the storm will flatten many crops, making it more difficult to harvest them, and Isaac's winds may cost farmers several hundred million dollars due to unharvestable crops. Still, the rains from Isaac will be highly beneficial for the success of the upcoming winter wheat season, and for next year's growing season.


Figure 2. Predicted precipitation for the five-day period ending on Tuesday evening shows that Isaac is expected to bring a large region of 3 - 6 inches of rain (red, orange, and brown colors) to Arkansas, Missouri, Illinois, Indiana, Ohio, and Kentucky. Image credit: NOAA/HPC.


Figure 3. The great drought of 2012 has brought so little rain to the Midwest that some areas require over 15" of rain (dark purple colors) to end the drought. Image credit: NOAA/CPC.

Unanswered questions about Hurricane Isaac

1. Did the passage of Hurricane Isaac stir up oil from the Deepwater Horizon oil spill? Isaac was the first hurricane to pass over the site of the 2010 Deepwater Horizon oil spill. We know that large hurricanes are capable of creating currents in deep water at the bottom of the Gulf of Mexico; Hurricane Ivan caused upwelling currents of 0.5 cm/s at a depth of about 500 meters. In an August 28 article in the Huffington Post, Nick Shay, professor of meteorology and physical oceanography at the University of Miami, said: "Winds will push water away from the center of a storm, which causes an upwelling as the ocean tries to adjust. It brings whatever is near the bottom up higher in the water column and currents can then push it towards the coast." Up to 1 million barrels of oil from the spill are estimated to still be present in the deep water sediment, on beaches, and in the marshes of Louisiana, and it is possible some of this oil will wash up on the Gulf Coast in coming months. The storm surge of Isaac also likely flushed out oil lodged in the coastal marshes of Louisiana, but it is unknown how much of a concern this might be.

2. What's the deal with these super-sized Category 1 and 2 hurricanes that have been hitting the U.S.? The past three landfalling hurricanes in the U.S.--Isaac (2012), Irene (2011), and Ike (2008)--have all been exceptionally large, among the top ten on record for horizontal extent of tropical storm-force winds. Each of these storms had an unusually low pressure characteristic of a storm one full Saffir-Simpson category stronger. Is this the new normal for U.S. hurricanes?

3. Did the new $14.5 billion upgrade to the New Orleans levee system cause worse flooding elsewhere? Whenever a new levee or flood control structure is created, you make someone else's flood problem worse, since the water has to go somewhere. Where did the water was stopped by the new $1.1 billion, 1.8 mile-long Lake Borgne flood barrier on the east side of New Orleans go? Did it flow south and contribute to the overtopping of the levees near Braithwaite? Or did it go north and contribute to the 36 hours of storm surge in excess of 5' observed along the Mississippi coast at Waveland? I posed this question to NHC's storm surge expert Jaime Rhome, and he said it was impossible to know without doing detailed storm surge modeling studies.

4. Can only hurricanes beginning with the letter "I" hit the U.S. now? Isaac (2012), Irene (2011), and Ike (2008) are the last three hurricanes to hit the U.S. It turns out that hurricanes that begin with the letter "I" and "C" have more names on the list of retired hurricanes than any other letter (nine each.) I'm thinking Isaac will get its name retired, letting storms beginning with "I" take over sole possession of first place on the retired storms list.

Hurricane Kirk in the Central Atlantic
Hurricane Kirk intensified into a 105 mph Category 2 hurricane this morning, becoming the 2nd strongest hurricane of the 2012 Atlantic hurricane season. Hurricane Gordon was the only stronger storm; Gordon hit sustained winds of 110 mph just before reaching the Azores Islands on August 18. Kirk has probably peaked in intensity, and is about to move over colder waters and gradually decay. Kirk is not a threat to any land areas.


Figure 4. Morning satellite image of Tropical Storm Leslie.

Tropical Storm Leslie a long-range threat to Bermuda, Canada, and the U.S. East Coast
Tropical Storm Leslie formed on Thursday in the Central Atlantic. Leslie's formation date of August 30 puts 2012 in 2nd place for earliest formation date of the season's 12th tropical storm. Only 1995 had an earlier formation date of the season's 12th storm. With records dating back to 1851, this year is only the second time 8 total storms have formed in August. The other year was 2004, when the first storm of the season formed on August 1 (Alex), and the 8th storm (Hermine) formed on August 29th. Satellite loops show that Leslie has a modest amount of heavy thunderstorm activity, and respectable low-level spiral bands and upper-level outflow. Conditions appear ripe to allow Leslie to intensify into a Category 2 hurricane by Sunday. Fortunately, Hurricane Kirk is weakening the ridge of high pressure to the north of Leslie, and Leslie is expected to turn to the northwest and miss the Lesser Antilles Islands. However, steering currents for Leslie are expected to collapse early next week, as Leslie gets stuck between two upper level lows. The storm will then slowly meander over the open ocean for many days, potentially threatening Bermuda. Leslie will stay stuck until a strong trough of low pressure approaches the U.S. East Coast around September 8. This trough should be strong enough to pull Leslie to the north and then northeast by September 9. At that time, Leslie may be close enough to the coast that the storm will make landfall in New England, Canada, or the Mid-Atlantic states. Leslie could also miss land entirely; this all depends upon the timing and strength of the September 8 trough of low pressure. Regardless, Leslie is expected to bring an extended period of high waves to the U.S. coast. According to NOAA's Wavewatch III model, large swells from Leslie will reach Bermuda by Monday, and arrive along the U.S. East Coast on Tuesday. These waves will be capable of creating dangerous rip currents and beach erosion.

Portlight disaster relief charity responds to Isaac
The Portlight.org disaster relief charity, founded and staffed by members of the wunderground community, are in Mississippi, helping out with Isaac relief efforts. You can check out their progress or donate to Portlight's disaster relief fund at the portlight.org website.

I'm planning on taking Saturday off, but will have a new post for you on Sunday. Have a great holiday weekend, everyone!

Jeff Masters

Hurricane Isaac Louisiana (apphotos)
People play in the storm surge from Hurricane Isaac, on Lakeshore Drive along Lake Pontchartrain, as the storm nears land, in New Orleans, Tuesday, Aug. 28, 2012. (AP Photo/Gerald Herbert)
Hurricane Isaac Louisiana
Portlight volunteers at Biloxi shelter (Portlight)
Portlight volunteers at Biloxi shelter
Hurricane Isaac Louisiana (apphotos)
Research students from the the University of Alabama measure wind speeds as Hurricane Isaac makes landfall, Wednesday, Aug. 29, 2012, in New Orleans, La. Isaac was packing 80 mph winds, making it a Category 1 hurricane. It came ashore early Tuesday near the mouth of the Mississippi River, driving a wall of water nearly 11 feet high inland and soaking a neck of land that stretches into the Gulf. The storm stalled for several hours before resuming a slow trek inland, and forecasters said that was
Hurricane Isaac Louisiana
TS Isaac (Raine911)
Between the rain bands
TS Isaac

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872. 7544
Quoting xtremeweathertracker:
Ok i just looked at the funktop imagery with Tropical Forecast points on.....is it my imagination or is the center of Leslie located under those cold cloud tops and well south and west of the NHC forecast points??? Just sayin!!!
yeap the nhc will relocate the coc soon imo
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871. denni
Hi, I'm am normally a lurker, but I noticed tonight that the names I follow during storms are almost the only ones on here tonight. It kinda got hectic during Isaac on this blog, but I always look for some of you guys. Thanks for being there, it helps.
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17.4N? 0.o
Member Since: July 6, 2010 Posts: 113 Comments: 32855
Quoting pottery:

Hmmmm.
What you think, 16.8 ??

edited from 15.8 to 16.8



That was at 00:12 GMT
and I am confident of at least 16.5 N
(likely a bit higher)

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868. Relix
Quoting trHUrrIXC5MMX:
is it my computer or they made changes here in the website with the fonts....?


They changed them
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Quoting Relix:
NHC at 17.2N at least... so sure of it :P
I agree, they won't change
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Quoting NativeSun:
Gro, I'm only 40 miles south of you, weve been really lucky the past few years, it's only a matter of time before our luck runs out.


We have been very lucky.
Member Since: July 17, 2009 Posts: 71 Comments: 27210
is it my computer or they made changes here in the website with the fonts....?
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Quoting xtremeweathertracker:
Ok i just looked at the funktop imagery with Tropical Forecast points on.....is it my imagination or is the center of Leslie located under those cold cloud tops and well south and west of the NHC forecast points??? Just sayin!!!
Another 2.5 to 3 degrees west without the stutter-step...and I would say that the trough has been missed.
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The market has closed. Some mention of "temporary jog" has closed the favorite at 9/5. Anything beyond that is a longshot.
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Quoting RTSplayer:


For the past decade, Levees seem to be far better suited to holding water in, rather than holding it out.


I was wondering -- instead of breaching levees to get water out, why can they just put a bunch of giant hoses over them to SIPHON the water out?
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Ok i just looked at the funktop imagery with Tropical Forecast points on.....is it my imagination or is the center of Leslie located under those cold cloud tops and well south and west of the NHC forecast points??? Just sayin!!!
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860. Relix
NHC at 17.2N at least... so sure of it :P
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...KIRK WEAKENS SOME MORE...
11:00 PM AST Fri Aug 31
Location: 33.9°N 49.5°W
Moving: NNE at 16 mph
Min pressure: 988 mb
Max sustained: 80 mph
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting trHUrrIXC5MMX:
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 01 SEP 2012 Time : 011500 UTC
Lat : 17:10:03 N Lon : 52:02:06 W


CI# /Pressure/ Vmax
3.9 / 991.4mb/ 63.0kt


Final T# Adj T# Raw T#
3.7 3.4 3.4

HURRICANE LESLIE according to this

Isaac had real low press. long before the winds came up, too.
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I'm gonna' go with 16.8 or 17 at 11PM.
My eyes don't know much but I'm just not seeing this decoupling thing. Maybe a stair-step relocation WWWSW??
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Gro, I'm only 40 miles south of you, weve been really lucky the past few years, it's only a matter of time before our luck runs out.
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CIMMS has 17.1N.
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854. Relix
Quoting JLPR2:


It would be ironic is Leslie ends up bringing more weather for us than Isaac. XD


Isaac was a joke. Big fat joke... for us at least. I know the NHC will go with the WNW movement and the usual 17 something latitude. Expecting it... but when someone like kman sees the same as I do, I get a little... how can we say this... nervous? Excited?
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Quoting NativeSun:
Grothar. nice graphic but it should be a thousand miles are so to the west right over Miami Ft. Lauderdale J/K maybe.


Thanks! :)
Member Since: July 17, 2009 Posts: 71 Comments: 27210
Quoting CaicosRetiredSailor:

Hmmmm.
What you think, 16.8 ??

edited from 15.8 to 16.8
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TWO YEARS AGO...

Hurricane EARL

ZCZC MIATCPAT2 ALL
TTAA00 KNHC DDHHMM
BULLETIN
HURRICANE EARL ADVISORY NUMBER 27
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072010
1100 PM AST TUE AUG 31 2010

...POWERFUL HURRICANE EARL CONTINUES MOVING NORTHWESTWARD...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...23.0N 69.9W
ABOUT 130 MI...210 KM NE OF GRAND TURK ISLAND
ABOUT 910 MI...1460 KM SSE OF CAPE HATTERAS NORTH CAROLINA
MAXIMUM SUSTAINED WINDS...135 MPH...215 KM/HR
PRESENT MOVEMENT...NW OR 315 DEGREES AT 15 MPH...24 KM/HR
MINIMUM CENTRAL PRESSURE...940 MB...27.76 INCHES
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Will be a super swell for the islands... and will stall for a while...

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Grothar. nice graphic but it should be a thousand miles are so to the west right over Miami Ft. Lauderdale J/K maybe.
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848. JLPR2
Quoting Relix:
Well, Leslie bringing in some fun here for me in the NE islands while tracking it. It will still fly to the NW eventually.


It would be ironic is Leslie ends up bringing more weather for us than Isaac. XD
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The oddest thing with this, is that Leslie has an immense core of cold cloud tops. You normally see this in a very strong developing system. That yellow indicates them.



Member Since: July 17, 2009 Posts: 71 Comments: 27210
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 01 SEP 2012 Time : 011500 UTC
Lat : 17:10:03 N Lon : 52:02:06 W


CI# /Pressure/ Vmax
3.9 / 991.4mb/ 63.0kt


Final T# Adj T# Raw T#
3.7 3.4 3.4

HURRICANE LESLIE according to this
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844. Relix
Won't worry until 11AM tomorrow. If same thing keeps happening I may freak out a bit
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Quoting washingtonian115:
Who's saying this season is a bust?.I said it's a fail because what everyone has thought about this season never came true.From the seasonal predictions to the intensity/track forecast.


Fail in many people's eyes is a bust, though I did understand the context you used it in.. having proficiency in understanding the "internet" as it where.
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Quoting CosmicEvents:
I haven't seen anything like that since I was 52.

HAHAHAHAHAHAH.
Whoooo !
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Member Since: July 17, 2009 Posts: 71 Comments: 27210
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Quoting sunlinepr:

Post 835.

Erie, man, Irie too.
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Quoting pottery:

Almost perfectly vertical.
I haven't seen anything like that since I was 52.
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The FIM8 still has a very powerful hurricane in the Atlantic in a few days.


Member Since: July 17, 2009 Posts: 71 Comments: 27210
Leslie trying to pull a Earl on us?
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834. Relix
Well, Leslie bringing in some fun here for me in the NE islands while tracking it. It will still fly to the NW eventually.
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833. Relix
Quoting 1900hurricane:
Really...?



Awesome... XD!
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Quoting 1900hurricane:
Really...?


Don't you love those?
Member Since: July 6, 2010 Posts: 113 Comments: 32855
a cyclone watch may be required
for the northern islands
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Quoting Bielle:


Wow! That's a huge area.


My nephew and sister are without e. power....
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Really...?

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Leslie you were suppose to obey your forecast track and stay away from land unlike fat Isaac...
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Quoting Terradad:


Are you sure about that 'old man'?

My best guess is W

But that is just a shot in the dark, so to say....

Very interesting, and hardly annoying!


Yes, Quite sure. But I am still awaiting the next CAT scan, I mean ASCAT to be positive.
Member Since: July 17, 2009 Posts: 71 Comments: 27210
Quoting CybrTeddy:


Realistically, I'm seeing a slow down in the insane activity we've been seeing, but by no means a crash. Probably 4 in September, giving us up to 16 named + 1 in October or November, giving us a total of 17 named, 8 hurricanes, and 2 major hurricanes (Leslie and another)

Maybe in the post season, Gordon could be upgraded to a major. I see no reason why not to, it's just a 1mph increase in winds...
Igor all over again...
I think 16-18 named storms is a reasonable forecast. I'm not going to give a forecast for hurricanes or majors, though.
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Given recent satellite trends, Tropical Storm Watches need to be issued for the northern Leeward Islands.
Member Since: July 6, 2010 Posts: 113 Comments: 32855
Maybe Lesilie missed the weak trough and will move a lot further west as the high builds in to the North and West.
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Quoting kmanislander:
If you believe it

Really impossible to say right now. All we can do is look at the last microwave imagery and extrapolate the current position
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Good evening all from beautiful Antigua. Very quiet in my neighbourhood but by the look of things it might not be come Sunday if Leslie has anything to say about it. Not worried though.
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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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