Dr. Jeff Masters' WunderBlog

Unanswered questions concerning Hurricane Isaac

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

+54

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 Issac
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)

Portlight volunteers at Biloxi shelter (Portlight)

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

TS Isaac (Raine911)

Between the rain bands

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2051. Hurricanes101 4:21 PM GMT on September 02, 2012
anyone have the 8am atcf coordinates for 99L? Member Since: March 10, 2010 Posts: 1 Comments: 6902

2052. RTSplayer 4:22 PM GMT on September 02, 2012
Wow... GFS has a colossal stall and takes pressure down to 972mb eventually. Member Since: January 25, 2012 Posts: 27 Comments: 875

2053. windshear1993 4:22 PM GMT on September 02, 2012
okay guys i looked at recent years and the 1936 atlantic hurricane season is a perfect anologue... 16-7-1 Member Since: June 1, 2012 Posts: 0 Comments: 66

2054. Articuno 4:23 PM GMT on September 02, 2012
Quoting RTSplayer: Yeah, we want one that goes out to see, like Katia. Member Since: October 22, 2011 Posts: 0 Comments: 1926

2055. wxchaser97 4:23 PM GMT on September 02, 2012
Another view of Leslie, who needs help fast, and 99L. Member Since: March 16, 2012 Posts: 87 Comments: 6785

2056. TropicalAnalystwx13 4:26 PM GMT on September 02, 2012
Quoting wxchaser97: Another view of Leslie, who needs help fast, and 99L. That's from 7:45 a.m. EDT this morning. Member Since: July 6, 2010 Posts: 89 Comments: 25283

2057. wxchaser97 4:26 PM GMT on September 02, 2012
GFS 00z run: GFS 12z run: Both have a strong hurricane stalling over Bermuda. Member Since: March 16, 2012 Posts: 87 Comments: 6785

2058. LiveToFish0430 4:27 PM GMT on September 02, 2012
Quoting wxchaser97: 2024, this year does not suck. Think of all the people affected by Isaac, Ernesto, Beryl, and Debby. They sure dont think this year sucks. Well, they might think it sucks, with all the flooding and damage, but i doubt they think its a bust Member Since: September 1, 2010 Posts: 0 Comments: 29

2059. washingtonian115 4:27 PM GMT on September 02, 2012
Quoting GTcooliebai: 156 hrs. Bermuda takes a direct hit! Look at the trough over the mid-west.Right out to sea. Member Since: August 14, 2010 Posts: 5 Comments: 10627

2060. WeatherNerdPR 4:27 PM GMT on September 02, 2012
Leslie reminds me of Fiona. A moderate TS passing North of the Antilles. Fiona passed closer, though. Member Since: July 7, 2010 Posts: 0 Comments: 5464

2061. Tazmanian 4:28 PM GMT on September 02, 2012
Quoting Hurricanes101: anyone have the 8am atcf coordinates for 99L? its still on 6:08am L, 99, 2012090206, , BEST, 0, 283N, 376W, 25, 1015, Member Since: May 21, 2006 Posts: 5088 Comments: 111341

2062. wxchaser97 4:28 PM GMT on September 02, 2012
Quoting LiveToFish0430: Well, they might think it sucks, with all the flooding and damage, but i doubt they think its a bust Well suck as in bust. They don't like the season due to the damage. Member Since: March 16, 2012 Posts: 87 Comments: 6785

2063. NOLALawyer 4:29 PM GMT on September 02, 2012
Quoting lobdelse81: So many garbage storms this year. I think this may be a record. Can anyone remember a season that has gone on to produce 12 named storms or more without yet producing a major hurricane??? Tell all of those people in and around New Orleans about how Isaac was just a garbage storm. I am sure they would agree with you, especially the ones who now have garbage, instead of homes. It does not take a major to be destructive and life changing. Member Since: September 3, 2009 Posts: 0 Comments: 517

2064. WunderAlertBot (Admin) 4:30 PM GMT on September 02, 2012
JeffMasters has created a new entry.

2065. lobdelse81 4:30 PM GMT on September 02, 2012
Quoting windshear1993: okay guys i looked at recent years and the 1936 atlantic hurricane season is a perfect anologue... 16-7-1 You may be right about the 1936 analogue. Hurricane #13 of 1936, could that be what Leslie ends up doing? Member Since: September 9, 2011 Posts: 0 Comments: 263

2066. stormchaser19 4:30 PM GMT on September 02, 2012
Quoting wxchaser97: GFS 00z run: GFS 12z run: Both have a strong hurricane stalling over Bermuda. Bermuda is in dangerous situation....when was the last time a major hurricane impact directly Bermuda? Member Since: June 20, 2012 Posts: 0 Comments: 1357

2067. wxchaser97 4:31 PM GMT on September 02, 2012
Quoting TropicalAnalystwx13: That's from 7:45 a.m. EDT this morning. You know I would post a certain gif but I wont cause I know what will happen. Anyway it still shows both of them. Is this better: Member Since: March 16, 2012 Posts: 87 Comments: 6785

2068. Hurricanes101 4:31 PM GMT on September 02, 2012
Quoting lobdelse81: So many garbage storms this year. I think this may be a record. Can anyone remember a season that has gone on to produce 12 named storms or more without yet producing a major hurricane??? Tell those affected by Beryl, Debby, Ernesto, Gordon and Isaac that this season has had so many garbage storms You really should think before you post something Member Since: March 10, 2010 Posts: 1 Comments: 6902

2069. wunderkidcayman 4:34 PM GMT on September 02, 2012
good morning guys Quoting wxchaser97: GFS 00z run: GFS 12z run: Both have a strong hurricane stalling over Bermuda. no no no no 00Z runs have the center stalling E of Bermuda and the 12Z runs have the center stalling W of Bermuda I think it could either head further W and stall further W missing Bermuda altogether or it stalls just off the W side of Bermuda and will get the worst from Leslie's "NE Corner" or as we Caymanians like to say "NorEast corner" Member Since: June 13, 2009 Posts: 2 Comments: 5409

2070. ILwthrfan 4:34 PM GMT on September 02, 2012
So looks like there going to be NO easy storm to track this hurricane season, Leslie looks to be yet another fickle storm to track. Dumped 2.5" of rain from the remnants of Isaac in the last two days here, and that is probably the least amount around the central parts of Illinois. It was definitely a much welcomed event up here as it should make a good little dent in our D3 drought. Most areas saw 2-4 inches, some areas 5 inches. Member Since: February 2, 2010 Posts: 0 Comments: 1029

2071. RTSplayer 4:47 PM GMT on September 02, 2012
Quoting wxchaser97: GFS 00z run: GFS 12z run: Both have a strong hurricane stalling over Bermuda. Model raw / Adjusted minimum pressure forecasts. 12z GFS 964mb / 956mb 06z GFDL 962mb / 966mb 06z HWRF 958mb / 959mb 00z Euro 973mb / 970mb (sept 07) 00z Euro 943mb / 940mb (lowest frame, sept 09) and and 168hrs (7p.m. Central September 8, or 00z September 9) and 120hrs, sept 7 Member Since: January 25, 2012 Posts: 27 Comments: 875

2072. hydrus 5:31 PM GMT on September 02, 2012
Way out, but if it were to happen, it would be potent. A sign that fall is rapidly approaching. Member Since: September 27, 2007 Posts: 1 Comments: 14271

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