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 Charmeck:


This is coastal carolina - no runoff from hillsides - it's flat!!! That is what we've been asking - how can this be happening so far from the center - but IT IS!!!!!
Its that chemtrail blob from Fl we got on east coast. Doc talks about it in blog post above.
Member Since: August 18, 2008 Posts: 0 Comments: 469
Good thing tides are currently going out - but they will peak again tomorrow morning.
Member Since: June 12, 2006 Posts: 0 Comments: 166
Quoting Charmeck:


The biggest problem is that all of the focus is on the "center of the storm". Yes I wouldn't want to be in the center of Isaac but I wouldn't be happy being where these outer bands are hitting either. Severe lightning, strange sounding thurder and torrential rain that just won't stop.
Nobody has had flooding like the Fla east coast. I shouldn't react to ignorant comments from trolls. Add the wind to the flooding and then you have some real problems like they may have in LA, MS, and AL.
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Quoting Levi32:
If Isaac moves north of the mouth of the Mississippi River, he will have an extra stretch of water and a favorably-shaped coastline that will help him continue tightening until final landfall.


This storm has a structure just like Hurricane Ike.
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Quoting physicseverywhere:
Seen a few comments on the rain along southeast coast.  Does seem like it was part of outer band of Isaac and as of right now we have 3-4 feet of water in the streets of Charleston, SC with high tide a few hours away.


yes that band is up around Georgetown SC now
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Quoting MississippiWx:


Recon had the strongest winds (flight level close to 110mph) in the eastern and northeastern areas.


Way up from last night......they were 70 at best.
Member Since: June 16, 2006 Posts: 0 Comments: 1565
EURO went east again. Probably no change for me. But looks like it sweeps NW through LA.
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Quoting Patrap:
Wish us well.


See y'all on the dry side..



Stay safe Pat.
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Hope everyone in the LA/MS areas stay safe.
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Barely inland in 48 hours. This illustrates the massive inland flooding threat.

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Quoting whetherboy:


Check out the image with figure 2 in the Doc's post. There appears to be numerous chemtrails associated with the convection over Florida. Perhaps there was a mad made effort to prevent moisture from being drawn into Isaac by pre-emptively triggering precipitation. This enabled the moisture to escape Isaac and be drawn north to a weak area of low pressure. It is well documented that numerous governments, including our own, engage in weather manipulation, and even the Doc noted that this event was the most "remarkable" aspect of Isaac.
Was very strange .. I never heard the booms like that before and the lightening strikes were many and incredible. Lemme know if you hear them in SC.. Doc does talk about it in his post though.
Member Since: August 18, 2008 Posts: 0 Comments: 469
Quoting MAweatherboy1:
Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 28th day of the month at 18:16Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 306)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 31
Observation Number: 24
A. Time of Center Fix: 28th day of the month at 17:42:20Z
B. Center Fix Coordinates: 28°28'N 88°50'W (28.4667N 88.8333W)
B. Center Fix Location: 128 miles (206 km) to the SE (145°) from New Orleans, LA, USA.
C. Minimum Height at Standard Level: 1,216m (3,990ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 59kts (~ 67.9mph)
E. Location of the Estimated Maximum Surface Wind: 43 nautical miles (49 statute miles) to the NW (320°) of center fix
F. Maximum Flight Level Wind Inbound: From 54° at 74kts (From the NE at ~ 85.2mph)
G. Location of Maximum Flight Level Wind Inbound: 43 nautical miles (49 statute miles) to the NW (321°) of center fix
H. Minimum Sea Level Pressure: 975mb (28.79 inHg) - Extrapolated
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 17°C (63°F) at a pressure alt. of 1,405m (4,610ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 22°C (72°F) at a pressure alt. of 1,524m (5,000ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 20°C (68°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character (Undecoded): SPIRAL BAND
M. Eye Shape: Elliptical (oval shaped)
M. Orientation of Major Axis in Elliptical Eye: 100° to 280° (E to W)
M. Length of Major Axis in Elliptical Eye: 80 nautical miles (92 statute miles)
M. Length of Minor Axis in Elliptical Eye: 70 nautical miles (81 statute miles)
N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 1 nautical mile
Remarks Section:
Maximum Flight Level Wind: 94kts (~ 108.2mph) in the east quadrant at 15:50:30Z
Sea Level Pressure Extrapolation From: 850mb


Flight level winds up to 94, from 66 late last night.....speaks for itself.
Member Since: June 16, 2006 Posts: 0 Comments: 1565
New 12z ECMWF still has Isaac offshore at 7am CDT tomorrow morning.

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Quoting dmh1026:
I think you are sadly mistaken, and have not been through anything more than a breeze based on your comment.


ive been through bertha, fran, bonnie, floyd, isabel, ernesto, charlie, ophelia and irene here in wilmington nc which = isaac is a little baby
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Quoting scott39:
Alcohol!

I knew that would be the first response!!
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all right I am just about packed and should be leaving around 4 pm central time. Hope all goes smooth and that I can find gas. Thanks for all the advice and links. I will blog when I get to the other side.
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I think if Isaac would have come into the Gulf with this structure, it probably would have bombed out into a Cat 3 or 4. This is certainly a dangerous situation along the Gulf Coast, but we're still lucky because it could be worse... He's just out of time now.

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Man, you have to be a true scum bag to do this stuff.

Hurricane Isaac looters hit boats south of Slidell, sheriff says

Link
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Wish us well.


See y'all on the dry side..

Member Since: July 3, 2005 Posts: 423 Comments: 128231
Did not if anyone noticed.The 1pm advisory stated that hurricane force winds extend out to then/ne 60 miles!thats a awful large swath for a cat one?
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Quoting ProgressivePulse:
Top winds appear to be in the NW quadrant as well.


Recon had the strongest winds (flight level close to 110mph) in the eastern and northeastern areas.
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Grand Isle about to face to main rain band, New orleans a thunderstorm. LINK has a loop version:

LINK

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Quoting leicaman:
I ntensifying

S oaking

A nnoying

A ________? (fill in the blank)

C aptivating

Astonishing
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Quoting leicaman:
I ntensifying

S oaking

A nnoying

A ________? (fill in the blank)

C aptivating

aggravating.
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Quoting Elena85Vet:


Don't forget about coastal Mississippi.

They don't get the press.

Quoting ScottLincoln:


Isn't that the "Land Mass Between New Orleans and Mobile" (tm)?


Don't forget there is a bit of "Bama" west of Mobile as well.
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Quoting RTSplayer:


That's insane.

I can only guess this is runoff from nearby mountains and foothills farther inland?!

How an it be that bad so far away from the storm, even with the feeder band merger into the trough? It seems like it should have run out of steam at some point?


This is coastal carolina - no runoff from hillsides - it's flat!!! That is what we've been asking - how can this be happening so far from the center - but IT IS!!!!!
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Power will not last long here now Uptown.

I will try to get some info to some dedicated members on the EOC Big Loop..but comm is ratty and sporadic on my end..

Member Since: July 3, 2005 Posts: 423 Comments: 128231
If Isaac moves north of the mouth of the Mississippi River, he will have an extra stretch of water and a favorably-shaped coastline that will help him continue tightening until final landfall.
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Joe Bastardi‏@BigJoeBastardi

Playing with fire.Like Ike, the tightening coming to the coast..this wind will show up.FLight level 94kts MAX FL WIND 94 KT E QUAD 15:50:00Z
Member Since: July 4, 2005 Posts: 204 Comments: 8871
HWY 90 along the beach in Bay St. Louis, MS this morning around 9:30. I'm sure it's worse than this by now.

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Quoting eyetoothtom1:
Wish for the best for all affected by this and future storms. As a little tyke whose family moved to MS Gulf Coast in "48 right after the Hurricane of 1948. That was not a direct hit there after hitting south Florida, but was bad. Went to LA or Tx after skimming MS. I've been thru or experienced the aftermath of all since. Lived in MS or Fl coast since, experienced first hand Camille, Fredrick, Geogeses, and Katrina (water to my nose @ 5 foot 6 inches nose height on land 22 feet above sea level, water swirling funiture around me, not like standing in a swimming pool that deep, floating my mother on her foam mattress with oxygen bottle. She perished nine months later from grief of losing her home since '48.

You see me as Eyetoothtom 1, I was on without the 1, back when IndianrRivergGuy posted often, he had recollection of the storm of '28 up the west coast of Fl. We chatted prior to Katrina. There was actually a link for members to contact each other. The chatting was not a post. Over the years with new computer and email address changes and lost password, couldn't sign on without new registry, thus the 1.

The blog has changed. Much bickering, I'm right, You're wrong. I predicted this two days ago. It used to be only information to help inform. And people are coming here for that.

Y'all have at it I guess. Me and ole timers like ole IndianRiverGuy will have to pass. I could never propose I'm right and you're wrong, or what's coming.

One P.S....yesteday Korinthman and some others were bemoning and saying they would get flack, but were so disappointed how weak was this storm. Bring on the next and make it better. You must not have seen the suffering? Sick!



Standing ovation from kctinney! :) I've been saying the same thing since Friday........hahaha
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Floodgates on the 17TH ST. Canal about to close. Waves are big on Lake Pontchartrain already.
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GFS has Issac on the coastline of La at 42 hours?
Member Since: June 16, 2006 Posts: 0 Comments: 1565
That spun off moisture from Isaac is starting to create grey clouds in SE Virginia.
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I take a nap and get up to a totally different storm.WOW! What a change.!
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Quoting Charmeck:
Isaac is HUGE and GOM is not the only area being affected - Almost knee deep water in downtown Charleston, SC. People - water is what kills not the winds!!!!!

Link


That's insane.

I can only guess this is runoff from nearby mountains and foothills farther inland?!

How an it be that bad so far away from the storm, even with the feeder band merger into the trough? It seems like it should have run out of steam at some point?
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Top winds appear to be in the NW quadrant as well.
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Quoting dmh1026:
I think you are sadly mistaken, and have not been through anything more than a breeze based on your comment.


The biggest problem is that all of the focus is on the "center of the storm". Yes I wouldn't want to be in the center of Isaac but I wouldn't be happy being where these outer bands are hitting either. Severe lightning, strange sounding thurder and torrential rain that just won't stop.
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Isaac is runing out of water and so are the recon
Member Since: May 21, 2006 Posts: 5091 Comments: 115072
LEVI - could you please give us your insight on steering. See my posts 683,691. Thanks so much!!
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Quoting leicaman:
I ntensifying

S oaking

A nnoying

A ________? (fill in the blank)

C aptivating
Alcohol!
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Quoting kctinney:


Isn't it pathetic that grown adults have to be treated like children? I have always been sickened by people that don't adhere to warnings and then put emergency pers. in danger because they have to be rescued! I personally think those individuals should be issued tickets vs being simply "questioned".


Yea depuity next door was called out for patrol about 2 hrs ago
Member Since: August 23, 2008 Posts: 0 Comments: 1918
Quoting Charmeck:

This is Charleston SC!
Link

Omg, a flood advisory! This is what I have been dealing with since Saturday.
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I give you "Isaac" the strongest 75 mph hurricane ever more than likely...

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Quoting AtHomeInTX:


Well that's definitely more than forecasted.


oy, yeah. Not liking this.
Member Since: September 5, 2007 Posts: 0 Comments: 3482
Quoting tennisgirl08:
According to latest steering maps, the weakness should be forcing Isaac more poleward. N, then NE. But because he is so weak, he is not feeling the weakness. I am not sure about the 10 NW mph movement, because the Plains ridge is fairly strong to his West and should block his movement. If he gains ANY strength he should start moving more NNW than WNW, but what do I know.

I think he may meander a little longer offshore than originally thought. This until he either:
a) gains more strength (moves north)
b) the ridge to the north starts to bridge with the A/B high pushing him west.

He will do what he wants, but any thoughts?
I believe he will gain more lattitue before going more W. I think we will see a LA/landmass landfall. Just joking Miss. Lol
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It can't be too bad yet, there are a lot of people walking the streets on their live cam
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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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