Isaac makes its final approach towards Louisiana

By: Dr. Jeff Masters , 3:29 PM GMT on August 28, 2012

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The winds and water are rising all along the coast from Louisiana to the Florida Panhandle as Tropical Storm Isaac makes its final approach. Two hurricane hunter aircraft in the storm are measuring a steadily lowering pressure and increasing winds aloft, but hurricane-force winds have not yet been observed at the surface. The 8:30 am center fix found a pressure of 976 mb, which is very low for a tropical storm. Top surface winds measured with the SFMR instrument were 70 mph, but the plane measured 102 mph at an altitude of 5,000 feet. It's more typical to see surface winds of 85 mph with a storm with these characteristics. Infrared and visible satellite loops and hurricane hunter reports from this morning have shown that Isaac has developed a 25-mile diameter eye, though the eyewall has not yet formed a full circle around the eye. Heavy thunderstorm activity is lacking on the north side, where light wind shear of 5 -10 knots is still pumping some dry air into the circulation.


Figure 1. Morning satellite image of Isaac. Note how dry air has wrapped into the west side of the storm, causing a lack of heavy thunderstorm activity.

Isaac's rains
One of the most remarkable features of Isaac has been the huge spiral band that parked itself along most of the east coast of Florida and remained there for an entire day, despite the fact the center of the storm moved 400 miles away. This rain band was amplified by a weak trough of low pressure along the East Coast, which pulled away from the coast Monday night, taking the band of heavy rain out to sea (except for a few lingering showers near West Palm Beach.) Isaac's heaviest rains fell along a swath from the east coast of Florida near West Palm Beach to the center of the state, just south of Orlando. The 2-day rainfall total of 9.03" at West Palm Beach brought their monthly rainfall total to 22.28", a new August record (old record: 20.12" in 1995.) Vero Beach's 6.48" of rain was a record for any August day. A possible tornado touched down there, damaging 20 mobile homes. In the Keys, rainfall totals as high as 7.94" (at Upper Matecumbe Key) were measured. Heavy rains from Isaac are lingering over Cuba but have ended in Haiti and the Dominican Republic; flash floods in Haiti from Isaac's torrential rains killed at least 24, and two died in the Dominican Republic. The big concern in Haiti is the heavy damage that was done to crops, and the likelihood that the storm's rains will worsen the cholera epidemic that has killed over 7,000 Haitians.


Figure 2. Radar-estimated rainfall from Miami, Florida radar shows that Isaac has dumped a wide swath of 8+ inches of rain (orange colors) across the state. Rainfall amounts in excess of 20" may have fallen just west of West Palm Beach, though the highest amount reported by a rain gauge was 13.10" at Greenacres in Palm Beach County.

Latest model runs for Isaac
The latest set of 0Z and 06Z (8 pm and 2 am EDT) model runs are fairly unified taking Isaac ashore near Southeast Louisiana late Tuesday night or early Wednesday morning, but continue to show some differences in what happens after that. Isaac may scoot nearly west-northwest just inland along the coast into Texas, as predicted by the ECMWF model, or head straight inland to the northwest and into Arkansas, as predicted by the GFS model. The latest 8-day precipitation forecast from the GFS model calls for 10 - 20 inches of rain over much of Louisiana. It appears likely that Arkansas will see some heavy rains of up to five inches, which would help put a dent in the exceptional drought conditions there.

Intensity forecast for Isaac
Low wind shear of 10 knots or less is likely until landfall, along with very warm ocean temperatures. An analysis of upper level winds from the University of Wisconsin CIMSS shows that Isaac's upper-level outflow is the strongest we've seen, with a solid outflow channel to the south. These conditions favor continued strengthening of Isaac until landfall. However, we've observed in the past many instances of hurricanes suddenly weakening in the final 12 hours before making landfall along the Central Gulf Coast. Katrina, Gustav, Dennis, Ivan, and Rita all did so. A July 2012 paper in the Bulletin of the American Meteorological Society by Rosenfeld et al. titled, AEROSOL EFFECTS ON MICROSTRUCTURE AND INTENSITY OF TROPICAL CYCLONES, theorizes that this may happen because of the impact of small particles that get pulled into the outer circulation of hurricanes, seeding the clouds. These small particles, primarily from air pollution, serve as the seed around which water condenses, increasing the rain in the outer spiral bands. The increase in rain and heat energy at the periphery of the storm comes at the expense of the eyewall and inner core, where the winds tend to weaken. A detailed modeling study by Khain et al. (2010) of Hurricane Katrina in the final day before landfall was able to reproduce the storm's weakening only when this air pollution effect was included. This impact of small particles on hurricanes is not included in any operational hurricane model.


Figure 3. Tide gauge data from Shell Beach, located in Lake Borgne just east of New Orleans. The green line shows the storm surge. The red line is the storm tide, the height of the water above Mean Sea Level (MSL.)

Storm surge observations from Isaac
Isaac's storm surge has peaked along the west coast of Florida. As I explain in our Storm Surge Tutorial, we are most interested in the storm tide--the height above Mean Sea Level (MSL) of the tide plus the storm surge. The storm tide is the number given in NHC advisories for how much above ground level the ocean will be at the coast. The storm surge is the extra elevation of the water due to wind blowing on the water, and does not include the action of waves on top of the water, nor the tide. Tide gauges are specially constructed so that transient waves do not impact water level measurements. At Cedar Key on the West Florida coast north of Tampa, a storm surge of 3' and storm tide of 3.8' were observed early this morning. These were the highest water levels measured at any tide gauge along the Florida west coast. Higher storm surges are occurring in the Florida Panhandle. As of 9 am EDT, here were the storm surge/storm tide measurements along the Florida Panhandle:

Apalachicola, FL: 3.5' storm surge, 4' storm tide
Panama City, FL: 2.3' storm surge, 3.3' storm tide
Pensacola, FL: 1.5' storm surge, 2.5' storm tide

A storm surge of 3.5 feet was recorded at 10 am EDT at Shell Beach on the east side of New Orleans in Lake Borgne. This site will have one of the highest surge values during Isaac; a storm surge of 9.5' was measured at Shell Beach during Hurricane Gustav in 2008.


Figure 4. Category 2 Hurricane Gustav of 2008 followed a very similar path to Isaac, and brought a storm tide (the combined effect of the storm surge and tidal levels) of up to 14.5' above ground level to the east side of New Orleans. Isaac's surge may be similar, though probably a little less, than Gustav's.


Figure 5. Track of Hurricane Gustav of 2008, which followed a path very similar to that of Isaac's predicted path.

Isaac: similar to Category 2 Hurricane Gustav of 2008 in destructive power?
Isaac is a huge and slow-moving storm, with tropical storm-force winds that extend out 205 miles from the center. Isaac has cut its forward speed down from 14 mph yesterday to 10 mph today, and a large swath of the coast will be subject to high winds and a large storm surge for an usually long period of time for a hurricane--up to 24 hours. Long duration winds are much more damaging than short duration winds, and a long duration storm surge event allows damage to occur during multiple high tide cycles. The long duration storm event will also allow very high rainfall totals, resulting in greater fresh-water flooding problems than usual. As a result, I expect Isaac's to cause more damage than the typical Category 1 hurricane. The 9:30 am EDT Integrated Kinetic Energy analysis from NOAA's Hurricane Research Division put the destructive potential of Isaac's winds near 2.3 on a scale of 0 to 6, but the destructive potential of Isaacs's storm surge was 4.1 on a scale of 0 to 6. For comparison, the storm surge destructive potential of Category 2 Hurricane Gustav of 2008 was rated at 4.2 on a scale of 0 to 6, and the wind destructive potential was 1.1--which is lower than Isaac's, even though Isaac was just a tropical storm at 9:30 am EDT. Gustav brought a storm tide (the combined height of the storm surge and high tide) of 14.5' to the east side of New Orleans, and 11' to Waveland, Mississippi. However, the destructive potential of Isaac's surge may be overrated by this analysis. Wave heights this morning from buoy and ships in Isaac have mostly been below 15', which is quite unimpressive. One ship report to the SE of the storm had a 19' wave height (thanks to meteorologist Steve Gregory for pointing this out.) With only another 12 - 18 hours over water, Isaac likely won't have time for its slowing increasing winds to build up a storm surge that will reach as high as 14', like Gustav did. The official NHC forecast of maximum storm surge height of 12' looks like a good one. The highest rainfall total observed in Gustav was 21" at Larto Lake, Louisiana, and I expect we'll exceed that for Isaac, since the storm is moving more slowly. Gustav spawned 41 tornadoes--21 in Mississippi, 11 in Louisiana, 6 in Florida, 2 in Arkansas, and 1 in Alabama. The strongest tornado was an EF2 in Evangeline Parish, Louisiana. Isaac will likely produce 10+ tornadoes. The total damage from Gustav in the U.S. was $4.5 billion (2012 dollars.) I expect Isaac's damage total will be in the $500 million - $4 billion range.

Invest 97L in the Middle Atlantic
A tropical wave (Invest 97L) is located in the Middle Atlantic, about 1250 miles west-northwest of the Cape Verde Islands. The storm has a modest amount of spin and heavy thunderstorms, and is under moderate wind shear. In their 8 am EDT Tropical Weather Outlook, NHC gave 97L a 40% chance of developing by Thursday morning. None of the reliable models foresee that 97L will be a threat to any land areas.

Another tropical wave that moved off the coast of Africa on Sunday is located just southwest of the Cape Verde Islands, and is moving west at 15 mph. Several models develop the disturbance into a tropical depression late this week, and NHC is giving the disturbance a 10% chance of becoming a tropical depression by Thursday morning. The disturbance could begin to affect the Northern Lesser Antilles as early as Saturday night, though our two best models, the GFS and ECMWF, predict the center of the disturbance will pass a few hundred miles north of the islands. The disturbance could be a long-range threat to Bermuda.

Jeff Masters

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Quoting zschmiez:


I work in the insurance industry, and don't know of any company who has a "by definition" hurricane deductible. Most are now named storm deductibles, and even that stipulation is ignored if there is enough damage.

Hurricane deductible is an old term that still sticks around, but means much different now.

If your provider abides by that rule, you need to get a new provider.
Wind deductible
Member Since: August 16, 2007 Posts: 0 Comments: 397
Quoting weathermanwannabe:
Hurricane ISAAC NESDIS Satellite | NDBC Obs | Storm Archive
...RECONNAISSANCE DATA INDICATE ISAAC FINALLY ACHIEVES HURRICANE STATUS... ...U.S. Warnings in Effect...


No discussion posted yet; just the headline......


They're not going to do a discussion. They did an update statement.

000
WTNT64 KNHC 281618
TCUAT4

HURRICANE ISAAC TROPICAL CYCLONE UPDATE
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
1120 AM CDT TUE AUG 28 2012

...RECONNAISSANCE DATA INDICATE ISAAC FINALLY ACHIEVES HURRICANE
STATUS...

REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT
INDICATE THAT MAXIMUM WINDS ASSOCIATED WITH ISAAC HAVE INCREASED
TO 75 MPH...120 KM/H. ON THIS BASIS...ISAAC IS BEING UPGRADED TO
A HURRICANE.

SUMMARY OF 1120 AM CDT...1620 UTC...INFORMATION
-----------------------------------------------
LOCATION...28.1N 88.6W
ABOUT 75 MI...115 KM SSE OF THE MOUTH OF THE MISSISSIPPI RIVER
ABOUT 160 MI...250 KM SE OF NEW ORLEANS LOUISIANA
MAXIMUM SUSTAINED WINDS...75 MPH...120 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 10 MPH...17 KM/H
MINIMUM CENTRAL PRESSURE...975 MB...28.79 INCHES

$$
FORECASTER STEWART/BEVEN
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Isaac looks better now ...

what great radar image ... thanks Patrap
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Please..the World is tuned in here..so Language must be cordial or well..u noes.

Use the iggy if someones annoy's you.

Thats how it is done.



New Orleans
NEXRAD Radar

Base Reflectivity 0.50° Elevation
Range 248 NMI





Member Since: July 3, 2005 Posts: 423 Comments: 127803
Quoting zschmiez:


I work in the insurance industry, and don't know of any company who has a "by definition" hurricane deductible. Most are now named storm deductibles, and even that stipulation is ignored if there is enough damage.

Hurricane deductible is an old term that still sticks around, but means much different now.

If your provider abides by that rule, you need to get a new provider.

In Texas, instead of a "hurricane deductible", it is usually "tropical cyclone", "windstorm" or "named cyclone" deductibles.
Member Since: August 3, 2008 Posts: 16 Comments: 5880
Quoting Tazmanian:
this storm could still make a run for cat 2

Quoting Tazmanian:



hes not wishcasting this could still be come at lest a 90 too 100mph storm

Thank you Taz

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Quoting weathermanwannabe:
Hurricane ISAAC NESDIS Satellite | NDBC Obs | Storm Archive
...RECONNAISSANCE DATA INDICATE ISAAC FINALLY ACHIEVES HURRICANE STATUS... ...U.S. Warnings in Effect...


No discussion posted yet; just the headline......



there wont be one in tell 4pm
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Quoting StormHype:
Live mobile streaming video from chaser currently at the water in Mobile AL:
Live video stream



Wow! It's partly cloudy, breezy (27 mph right now), and there are some waves breaking over some unknown kind of thing in the background. Pressure is 29.73 and rising. Yep, those chasers are right at ground zero. :)
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Quoting wunderkidcayman:

I will not stop it because I am not wishcasting right so you and the rest of you guy SHUT UP about me wish casting I am not FREAKING WISHCASTING jesus Christ people what the hell is wrong with you



thats a good way in geting bannd
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Hurricane ISAAC NESDIS Satellite | NDBC Obs | Storm Archive
...RECONNAISSANCE DATA INDICATE ISAAC FINALLY ACHIEVES HURRICANE STATUS... ...U.S. Warnings in Effect...


No discussion posted yet; just the headline......
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Member Since: July 4, 2005 Posts: 204 Comments: 8806
364. yoboi
how many miles from land is the center at now?
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Quoting LAlurker:

Depending on your policy - "hurricane" deductibles are much higher - more $ out of your pocket. Fema doesn't care about storm status, only "disaster" declaration.
Thanks! I knew I might be way off as I had private homeowners after Jeanne and Francis and no FEMA dealings except that they reimbursed us for the small portable generator we bought because my dad needed oxygen and was undergoing Chemo and radiation at the time.

Thanks for the clarification, truly.

Truly.
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Quoting StormHype:
Insurance companies breathing a sigh of relief now that it's officially a hurricane. Now the claimant must pay a big hurricane deductible before their insurance providers incur any liability.


I work in the insurance industry, and don't know of any company who has a "by definition" hurricane deductible. Most are now named storm deductibles, and even that stipulation is ignored if there is enough damage.

Hurricane deductible is an old term that still sticks around, but means much different now.

If your provider abides by that rule, you need to get a new provider.
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Quoting LAlurker:
According to radar- the "eyewall" is about to make landfall at the mouth of the river.

According to the hurricane hunter aircraft, still a ways to go.
Member Since: August 3, 2008 Posts: 16 Comments: 5880
Quoting fireflymom:
No ant or bird behavior post today.
Animals don't wait for the NHC to start their preps; I imagine finishing preps before conditions begin deteriorating would help survival rates...
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Member Since: July 3, 2005 Posts: 423 Comments: 127803
Looks like the HH about to make another center pass.
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Finally the nhc upgraded to cat 1 Issac now,11:20 cdt.
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According to radar- the "eyewall" is about to make landfall at the mouth of the river.
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Quoting depalma13:


Stop it. It's not going to happen, so stop wishcasting.



hes not wishcasting this could still be come at lest a 90 too 100mph storm
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What is it with these tropical storms and hurricanes nowadays!? They have just declared Isaac a hurricane and there is no eye whatsoever on satellite. It's like the center has marbles in it preventing it from making a proper center with an eye. This happened to Gustav and Ike as well, I might be crazy, but is this some sort of man-made hurricane reduction technique? I could see it, "Throw some sort of degrading substance in the center of the storm to make it not be able to form a proper eyewall and eye." I know, though, that Ike and Gustav did have eyes on radar at landfall, but over the Gulf it was like what I described above, and it took them really long to strengthen or they weakened.
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Oh my!.Isaac is a hurricane and he is going to slam into NOLA as a cat 5!.What's the difference between a 70mph storm and a 75mph storm? in terms of impact?.Nothing really.Isaac will still bring the same affects.
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this storm could still make a run for cat 2
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Quoting wunderkidcayman:
I wounder guys what would happen if Hurricane Isaac rapidly tighten it circulation and he rapidly make a run to strong Cat 2 boarder cat 3


Stop it. It's not going to happen, so stop wishcasting.
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One should never put credence for a storm more than 5 days out, especially one that hasn't formed yet. Isaac should have taught us that.
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Quoting lurkersince2008:
Thanks TreasureCoastFl....
You're welcome. But you know these things could change in a blink so prepare for the worst and hope for the best ;)
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raining steadily since about 10 in atlanta.  love those rain bands.
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The moisture is finally filling in near the center. Note how much larger the rain area is:

NOW



1 hour 20 minutes ago:

Member Since: December 28, 2010 Posts: 0 Comments: 134
Quoting Felix2007:
I disagree with this. On September 9? Really?


is it illegal for there not to be a storm on september 9th?

nice high over the NE btw, if kirk stays weak enouth to skip from the AB high to the NE usa high, we could have trouble but i doubt it....seems to be a recurve in 5days or less
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I see the season shutting down very quickly after first week of september. WIth a developing el nino and the mjo not being in atlantic for the month of september we are gonna have a very lackluster peak of season
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Quoting Felix2007:
I disagree with this. On September 9? Really?


The downward phase of MJO arrives in Atlantic.
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342. hercj
Levi is right. This system will be strengthening at landfall. There is a world of difference between a system that is strengthening and one that is losing structure. The last one I remember getting stronger at landfall was Katrina when she went into Florida. Cantori was on the streets yelling into his microphone "this is the strongest cat 1 hurricane I have ever seen".
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STORM 09L
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Thanks TreasureCoastFl....
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Quoting Felix2007:
252 hours, relatively quiet, seems suspicious...


Felix, everything at 252 hours (10.5 days) seems suspicious.:) Given the model performance with Isaac, are you really giving any credence to the long range model runs? Didn't we just go through this all the way from Africa with Isaac?
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348
Member Since: July 12, 2008 Posts: 7 Comments: 383
Quoting wxmod:
From the blog above (figure 2), Dr. Masters has posted an amazing satellite of chemtrails induced rain.



Interesting. If we assume that these are chemtrails being used to induce rain, can someone explain the purpose of using them in this case? Would it inhibit intensification of Isaac by infusing more dry air? If so, would this have caused Isaac to travel further west? Can some of you knowledgable posters provide any insight? Not to debate whether they are chemtrails, but to explain the impact(s) IF they are.
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Quoting tropicfreak:


Look who returned....

I never left
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12z GFS precip map through 120 hours..my area seems to be in one big rain event and we dont even have a hurricane affecting us..

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Quoting Dsntslp:
IMO they are cheering for two reasons.

One, it is generally thought by some that if the storm is labelled as a TS a good many people will not take it as seriously as if it were a hurricane. This is supported by employers that have non essential employees coming into work during this mess and not cancelling, IMO.

Two, I am not sure of this and somebody who knows for sure please correct me and expound on this but the label of hurricane in and of itself means a greater possibility of sustained damages being covered by insurance companies and also may mean that more people, without homeowners coverage, qualify for FEMA assistance after the storm. (Run on sentence, I know, lol).

Long story short, I do believe they are cheering because hurricane status v TS status means that "What's in a name" will now work to the benefit of the general public in the short and long run.

Depending on your policy - "hurricane" deductibles are much higher - more $ out of your pocket. Fema doesn't care about storm status, only "disaster" declaration.
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img src="">
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2 weeks out but still shows nothing.
Member Since: July 12, 2008 Posts: 7 Comments: 383
Quoting LongGlassTube:


Totally irresponsible for the NHC to call a storm with 976 millibars of pressure a TS.

What is up?

My wife is expected to go to work tomorrow in a nonessential business because it is ONLY a TS.

They are blowing it!

I'm a Fire Fighter and EMS responder here in Ascension Parish. We were told to expect 48 hours of TS force winds and 12 hours of Hurricane force winds within our Parish.....


Clearly you have a right to be upset at the situation, however please reconsider and don't blame the NHC for the obvious poor judgement of your wife's employer. Your city is under a hurricane warning. My employer closes its doors without exception for a hurricane warning. The NHC has been very clear that they expect Isaac to be a hurricane when it comes ashore tonight and dangerous conditions may linger for 24 hours post landfall.

If your wife's employer is irresponsible enough to require non-essential employees to work under those conditions, then it is the employer's fault not the NHC. The NHC has no responsibility to write and implement emergency response policies for businesses, governments or individuals. They provide the information in as understandable and non-jargon laced language as possible.

They provide parameters for flood potential, rain potential and wind strengths. It is up to the people in the path of the storm to respond appropriately. I hope you and your family, and everyone in Isaac's path, will remain safe and that any damage is minimal. Good luck.

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Live mobile streaming video from chaser currently at the water in Mobile AL:
Live video stream

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Quoting StormHype:
Insurance companies breathing a sigh of relief now that it's officially a hurricane. Now the claimant must pay a big hurricane deductible before their insurance providers incur any liability.


you got that right
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I disagree with this. On September 9? Really?
Member Since: July 12, 2008 Posts: 7 Comments: 383
327. MahFL
Looks like a new bigger eye is trying to form, never good.
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Quoting Felix2007:
I'm surprised that it's forecast to be this quiet during the peak of the season.


still too early to tell hmm it even too early to tell if PRE-98L will miss the islands or if it will go Burmuida its just too early
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don't know if this has been addressed, but NOLA and those along the Mississippi river, i'm thinking, are going to be buffered from the full effects of any storm surge due to very low river levels. a saving grace perhaps? for some, maybe..
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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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