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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1524. reef58
You seem to be the one that is upset. The storm is what it is, and that is a cat1 hurricane. Or put another way not much weaker than the storm your user name references.

Quoting HurricaneIsabel:


I know. Most guys on this site would call a tropical depression a major hurricane. It's sickening to see most wish these storms were stronger and false cast these storms. Isaac isn't significant, maybe next year guys. Probably will make landfall as tropical storm, I know this will make most of you upset. Also, the storm surge isn't bad at all. Most won't lose power, Minor flooding, Biggest threat is tornados.
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Upcoming Recon mission should find at least 75kt cyclone; bet on it.
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Quoting Patrap:
Name: Isaac
MoreEmail
Looking for reactions to this name? Ask our community!
Name Search


GO

Origin and Meaning of the Name Isaac Debate this name info

Gender:
Boy

Origin:
Hebrew

Meaning:
He will laugh

Pronunciation:
(I zak) [Guide]

Form of:

Yitzchak



he is laughing
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Hurricane forced sustained winds and close to 100 mph gusts now occurring on the KMIS oil platform:

Station KMIS
Federal Aviation Administration
Location: 29.296N 88.842W
Date: Tue, 28 Aug 2012 20:55:00 UTC
Winds: SSE (150°) at 69.0 kt gusting to 85.1 kt
Air Temperature: 80.6 F
Dew Point: 77.0 F
Visibility: 0.2 nmi

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View from my screen porch. The east side of Isaac be rockin'.

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Quoting HurricaneIsabel:


I know. Most guys on this site would call a tropical depression a major hurricane. It's sickening to see most wish these storms were stronger and false cast these storms. Isaac isn't significant, maybe next year guys. Probably will make landfall as tropical storm, I know this will make most of you upset. Also, the storm surge isn't bad at all. Most won't lose power, Minor flooding, Biggest threat is tornados.

I'll start preparing a nice helping of crow...
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Panhandle starting to get another band and possible more.. Good luck LA,MS, AL and the panhandle of FL.. We will get through this..
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He's been a tricky storm! We thought we had a bullseye on us in Destin/Niceville (3 days ago) and bizarre Isaac has defied us! Here on the bay we have a surge of a couple to 3 feet, no rain today & gusty winds around 30mph. Mid day was gorgeous, sunshine... A tricky storm indeed!
Quoting moonlightcowboy:


You ask hard questions! ;)

He can only do one of two things:
1. Come inland, degenerate.
2. Get blocked with the plains high bridging with the weak, lateral trough lifted out. Stalling partially over land/water, maybe even heading back out to sea.

Sssshhhhh! It'll most likely be #1; but, don't repeat this, but it would not totally surprise me if the latter happened! ;)
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1515. Patrap
Name: Isaac
MoreEmail
Looking for reactions to this name? Ask our community!
Name Search


GO

Origin and Meaning of the Name Isaac Debate this name info

Gender:
Boy

Origin:
Hebrew

Meaning:
He will laugh


Pronunciation:
(I zak) [Guide]

Form of:

Yitzchak
Member Since: July 3, 2005 Posts: 421 Comments: 127633
Quoting moonlightcowboy:


You ask hard questions! ;)

He can only do one of two things:
1. Come inland, degenerate.
2. Get blocked with the plains high bridging with the weak, lateral trough lifted out. Stalling partially over land/water, maybe even heading back out to sea.

Sssshhhhh! It'll most likely be #1; but, don't repeat this, but it would not totally surprise me if the latter happened! ;)

(◕‿-)
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Quoting Patrap:


A Downhill trend I think.
Pat im at 45 mph NNE near the lakefront
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1455 CybrTeddy Didn't notice that Indianrivguy was back

Never left, jes showin' himself less often. Probably been poppin' in when you weren't readin' the blog.
Member Since: August 21, 2007 Posts: 0 Comments: 4860
Quoting Charmeck:
Link
They were earlier today - if you look at the "flash" image on this link you'll see the connection getting bigger.


Hmmm, could nearly say the biggest cane EVER...stretching in some way from central Mexico to off the coast of N/S Carolina :o
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He's expanding and looking much better on satellite.

I am in those NE outer feeder bands and I am not that impressed. Heavy rain, 20-30 mph only gusting. I get worse conditions in afternoon thunderstorms. Still havne't lost power.

Will be interesting to see what the night brings.
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Quoting TheHurricaneDundee:
Hope it doesnt. It'd suck if they gave a name to a widdle thunderstorm

I'm interested in seeing the name Leslie be attached to a formidable hurricane. That'd be interesting. lol
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blob reveals the fang...
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1504. Patrap
A Curfew is effect for St. Charles Parish from 6pm CST till 8 am tomorrow morning.

Do not venture out unless one is in a Emg Mode or Incident...
Member Since: July 3, 2005 Posts: 421 Comments: 127633
Quoting justsouthofnola:


gusting
they predicting it will soon as the COC gets closer
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Wind direction shift at 4pm cst to NE-50 at pstl1 suggests another small jog west! Pressure down to 28.91inches, and the pressure at LOP1 is also falling really fast, so the storm will probably shoot the gap between the center of these two stations, headed WNW, towards the coast just south of Houma.
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Quoting Patrap:
This is B-A-D Mojo...


The "Post-Katrina System" test...on the anniversary...yep...I'd agree...bad mojo indeed. Stay safe!
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Quoting moonlightcowboy:


You ask hard questions! ;)

He can only do one of two things:
1. Come inland, degenerate.
2. Get blocked with the plains high bridging with the weak, lateral trough lifted out. Stalling partially over land/water, maybe even heading back out to sea.

Sssshhhhh! It'll most likely be #1; but, don't repeat this, but it would not totally surprise me if the latter happened! ;)


If that mid level ridging builds in a little stronger than forecast, number 2 becomes a realistic option. I truly hope not.
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Quoting scott39:
Maybe New Orleans will a better ride on the West side.



that means we get it worse-___-
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Aw, sweet, another recon is going out, I thought they were done... If those earlier flight level winds have worked down he could be at 90mph or so right now.

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Quoting TropicalAnalystwx13:

Yeah...but it's not going to.




like it or not its going too be come the K storm 1st
Member Since: May 21, 2006 Posts: 5091 Comments: 114760
Quoting synthvol:
Conditions at KMIS, Oil Platform
29.296 N 88.842 W (29°17'46" N 88°50'31" W)
Anemometer height: 85 m

Wind Direction (WDIR):SSE ( 150 deg true )
Wind Speed (WSPD): 69.0 kts
Wind Gust (GST): 85.1 kts
Air Temperature (ATMP): 80.6 °F
Dew Point (DEWP): 77.0 °F
Visibility (VIS):0.2 nmi
Link:
Link


Thanks.
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Quoting tennisgirl08:


MLC - that's what I keep thinking, too - but the NHC seems to disagree.

Here in Mobile, Al getting heavy rain with 20-30 mph gusts. But still have power.
just got power back for 2nd time.
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1494. Patrap
Member Since: July 3, 2005 Posts: 421 Comments: 127633
Quoting tennisgirl08:


After Isaac, I am going to be tired of tracking. There is so much dry air in the ATL right now I doubt we will see any Major Hurricanes this year.



Gordon was a borderline Category 2/3 storm out in the north central Atlantic under pretty unfavorable conditions, so there's definitely opportunities for storms to become powerful this year. Particularly during the peak of the season next month.
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Quoting TheHurricaneDundee:
Hope it doesnt. It'd suck if they gave a name to a widdle thunderstorm
Oh please
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1491. scott39
Maybe New Orleans will get a better ride on the West side.
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Quoting Tazmanian:




the NHC has it be comeing a TS may be tonight



FORECAST POSITIONS AND MAX WINDS

INIT 28/2100Z 23.8N 43.9W 30 KT 35 MPH
12H 29/0600Z 24.1N 45.3W 35 KT 40 MPH
24H 29/1800Z 24.3N 47.4W 35 KT 40 MPH
36H 30/0600Z 24.6N 49.6W 35 KT 40 MPH
48H 30/1800Z 25.3N 51.7W 35 KT 40 MPH
72H 31/1800Z 27.5N 55.5W 35 KT 40 MPH
96H 01/1800Z 32.5N 55.0W 35 KT 40 MPH
120H 02/1800Z 40.0N 48.0W 35 KT 40 MPH

Yeah...but it's not going to.
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expanding, and fast

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symmetrical storm
Member Since: June 20, 2012 Posts: 0 Comments: 2150
Quoting lopaka001:


That's a lot of high pressure to the north it seems Isaac has nowhere to go but NE eventually no?


You ask hard questions! ;)

He can only do one of two things:
1. Come inland, degenerate.
2. Get blocked with the plains high bridging with the weak, lateral trough lifted out. Stalling partially over land/water, maybe even heading back out to sea.

Sssshhhhh! It'll most likely be #1; but, don't repeat this, but it would not totally surprise me if the latter happened! ;)
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Quoting mobilebayal:


You are on the hill of doom..lol. I have a natural gas generator that runs the house. I am spoiled!
Me too! My wife's friend on Chelsea has one but itdidn't auto start (she moved in the 2 weeks ago). She got it going. BTW, we're on generator now.
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Quoting HurricaneIsabel:
reedzone is still here wish casting hoping for a strong cat 5 to hit land? Sorry dude. This is borderline tropical storm, just some sprinkles here and there.
You must have some serious Lil man Syndrome or something, please go play somewhere else. If you need that much attention do it somewhere else and let genuine conversation take place...Geez some people.
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1483. Patrap
nola.com


HURRICANE ISAAC
Isaac leaves thousands without power in Lafourche, Plaquemines
Richard Thompson The Times-Picayune
HURRICANE ISAAC
NOPD officers will work 12-hour shifts during Hurricane Isaac
Ramon Antonio Vargas The Times-Picayune
Read an e-edition of The Times-Picayune
Staff The Times-Picayune
Member Since: July 3, 2005 Posts: 421 Comments: 127633
Quoting sdcbassman:


Hey oracle. You and I have been on here long enough to realize that is reed for ya. Mr. Hyped-up doom-caster. Yet when someone calls him on his ridiculousness, he basically cries about people picking on him. He should really grow a pair. If you put yourself out there like that -- expect to deal with people calling you on it.


I know, but he's hard to follow, I would love to learn from him, but then he posts ridiculous claims.

It's hard for me to tell fact from fiction on here, that's the frustrating part.
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Quoting TropicalAnalystwx13:

Yep. Right here.

It'll dissipate tomorrow though, so I'm not worried about it taking the name "Kirk" from the wave off Africa.





the NHC has it be comeing a TS may be tonight



FORECAST POSITIONS AND MAX WINDS

INIT 28/2100Z 23.8N 43.9W 30 KT 35 MPH
12H 29/0600Z 24.1N 45.3W 35 KT 40 MPH
24H 29/1800Z 24.3N 47.4W 35 KT 40 MPH
36H 30/0600Z 24.6N 49.6W 35 KT 40 MPH
48H 30/1800Z 25.3N 51.7W 35 KT 40 MPH
72H 31/1800Z 27.5N 55.5W 35 KT 40 MPH
96H 01/1800Z 32.5N 55.0W 35 KT 40 MPH
120H 02/1800Z 40.0N 48.0W 35 KT 40 MPH
Member Since: May 21, 2006 Posts: 5091 Comments: 114760
Quoting synthvol:
Conditions at KMIS, Oil Platform
29.296 N 88.842 W (29°17'46" N 88°50'31" W)
Anemometer height: 85 m

Wind Direction (WDIR):SSE ( 150 deg true )
Wind Speed (WSPD): 69.0 kts
Wind Gust (GST): 85.1 kts
Air Temperature (ATMP): 80.6 °F
Dew Point (DEWP): 77.0 °F
Visibility (VIS):0.2 nmi
Link:
Link
Seems to confirm the NHC's 70kt intensity.
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Quoting StormHype:
There should be a ban for posting more than one image. Someone broke the blog and i think we know who.


All the images are hosted offsite anyways the only thing that slows down the blog is too many people posting.
;=)
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Member Since: July 14, 2008 Posts: 1 Comments: 9628
Quoting TropicalAnalystwx13:



this storm all most look like IKE he had a big EYE
Member Since: May 21, 2006 Posts: 5091 Comments: 114760
Quoting wxgeek723:
Um....what?

...NEW TROPICAL DEPRESSION FORMS OVER THE EASTERN ATLANTIC...NO THREAT TO LAND...

Yep. Right here.

It'll dissipate tomorrow though, so I'm not worried about it taking the name "Kirk" from the wave off Africa.

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Quoting TropicalAnalystwx13:


they just keep coming
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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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