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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Isaac is finally pulling that moisture around to his N/NE quadrants.

It's been stuck on his south side for a couple days while his north side had been taking in the dry air.
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Quoting NCHurricane2009:

What...so they finally got a hurricane force wind measured in an area not contaminated by heavy rain? How high was sustained the measurement?
66 knots. (About 76mph)
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Quoting sullivanweather:
The tornado threat with Isaac may be higher than normal for a landfalling tropical storm due to presence of all that mid-level dry air and the fact that since this storm's beginning, it seems, the mid-level center and the low-level center have never seemed to quite line up with each other. This should create much more directional shear between the low and mid-level vectors.

So the dry air allows more sunshine over land, increasing the low-level instability, feeder bands move through with their enhanced shear, more tornadoes result.


+++++++, great post, Sully! Thanks.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
Mission 30 concluded.
Mission Status: Concluded (Last Report)
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Quoting MississippiWx:


This is the oh-so precious SFMR reading that the NHC was waiting on.

What...so they finally got a hurricane force wind measured in an area not contaminated by heavy rain? How high was sustained the measurement?
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Afternoon All.

Prayers to those in the path of Isaac, time to hunker down as he looks to be tightening up.

In my trip out to Wellington I came across the staging ground for electricians, must have been 500 trucks there and 50 or so tour buses. Looked like they were getting ready to head North. Help is on the way..

I made a blog that includes pics of the flooding in Wellington, FL. Thank the lord Isaac let go of the band that had been plaguing the east coast. Not a moment too soon as many in Wellington were facing complete inundation.
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108 hours
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Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 28th day of the month at 16:00Z
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: 15
A. Time of Center Fix: 28th day of the month at 15:34:30Z
B. Center Fix Coordinates: 28°07'N 88°30'W (28.1167N 88.5W)
B. Center Fix Location: 159 miles (256 km) to the SE (144°) from New Orleans, LA, USA.
C. Minimum Height at Standard Level: 1,217m (3,993ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 55kts (~ 63.3mph)
E. Location of the Estimated Maximum Surface Wind: 24 nautical miles (28 statute miles) to the W (261°) of center fix
F. Maximum Flight Level Wind Inbound: From 347° at 59kts (From the NNW at ~ 67.9mph)
G. Location of Maximum Flight Level Wind Inbound: 50 nautical miles (58 statute miles) to the W (265°) of center fix
H. Minimum Sea Level Pressure: 975mb (28.79 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 18°C (64°F) at a pressure alt. of 1,527m (5,010ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 22°C (72°F) at a pressure alt. of 1,519m (4,984ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 19°C (66°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
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: 2 nautical miles
Remarks Section:
Maximum Flight Level Wind: 94kts (~ 108.2mph) in the east quadrant at 15:50:00
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Mobile radar is looking up a lot higher since it's farther away than Slidell, but it is showing broad area of sustained winds above 50kts and 80kts thresholds on the western eye wall, probably at flight level or so by the time you get that far away.
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Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 28th day of the month at 16:00Z
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: 15
A. Time of Center Fix: 28th day of the month at 15:34:30Z
B. Center Fix Coordinates: 28°07'N 88°30'W (28.1167N 88.5W)
B. Center Fix Location: 159 miles (256 km) to the SE (144°) from New Orleans, LA, USA.
C. Minimum Height at Standard Level: 1,217m (3,993ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 55kts (~ 63.3mph)
E. Location of the Estimated Maximum Surface Wind: 24 nautical miles (28 statute miles) to the W (261°) of center fix
F. Maximum Flight Level Wind Inbound: From 347° at 59kts (From the NNW at ~ 67.9mph)
G. Location of Maximum Flight Level Wind Inbound: 50 nautical miles (58 statute miles) to the W (265°) of center fix
H. Minimum Sea Level Pressure: 975mb (28.79 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 18°C (64°F) at a pressure alt. of 1,527m (5,010ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 22°C (72°F) at a pressure alt. of 1,519m (4,984ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 19°C (66°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
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: 2 nautical miles
Remarks Section:
Maximum Flight Level Wind: 94kts (~ 108.2mph) in the east quadrant at 15:50:00Z
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Quoting jeffs713:

Based on that map, southern Mississippi and Alabama won't be getting any rain. Lucky them! (hehe)


It sure looks that way in AL, durn it. We really need the rain for the cotton and soybean crops. Corn is already long dead. The rain bands certainly look unimpressive now. Georgia and South Carolina may end up getting more from Isaac's ex-blob than we will.
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There are some good points about NOT under-estimating the potential this storm brings despite the lack of intensification (at least intensification in the sense we are used to). Here are some quotes from what I posted on my blog this morning to emphasize to everyone being affected that might be under-estimating Isaac

"Impact statement (c) highlights the storm surge threat...which is going to be more significant than usual for a tropical storm/minimal hurricane....as the creation of the large tropical storm wind radius stirs up a large amount of water...so all mandatory evacuation orders along the US Gulf coast should have been obeyed despite the less-than-expected intensification of the storm."

"Impact statement (b) makes a point about an emerging flood risk when the storm slows and associated heavy rains persist over the same area. Impact statement (b) also emphasizes that heavy rains can be expected in squalls outside of the shown impact swath. For example...Palm Beach on the east Florida coast saw a persistent squall of heavy rain for several hours that created unexpected flooding...despite having been outside of my drawn impact swaths for the last couple of forecasts"
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Quoting ckeusa:
In a previous blog post, Dr. Masters noted that the ideal situation to break the drought in the U.S. would be a big, wet category 1 hurricane making landfall along the Gulf Coast. TS Isaac is the exact scenario that was described (only with slightly weaker winds!), yet this storm is certainly not being treated as a good thing. What gives?

The "landfall along the Gulf Coast" part.
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Kirk gaining strength, and Isaac's remnants still sitting there. 102 hours
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Quoting guygee:
The dry air was not there all along, rather Isaac had an envelope too large for its own good. It was so large it kept sucking in the subsidence created by it own collapsing convection, and it could not spin up enough to mix that dry air out.

From my perspective on the FL east coast I got heavy rains both on the east and the west sides of Isaac. Most well-organized storm give me a good dose of subsidence on the west side, but not Isaac.


To a certain extent I agree... since it had semi optimal conditions when it was closer to the FL W coast, but other conditions prevented it from acquiring an inner core. At that point it was smaller than what it is now and it still struggled.

Before that it had dry air to deal with from Cuba/NW Carib and now dry air from CONUS which gets an extra boost from the subsidence generated by Isaac himself.
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Quoting truecajun:
are sandbags for only lowlying areas and neighborhoods that have a history of flooding?

we live in a newish neighborhood. we built about 6 years ago. we've never had problems with flooding. does that mean that we most likely will not with this storm??

where are you located?
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159. yoboi
Quoting AtHomeInTX:
Stair stepping its way into TX. We might get a little more than wind shift.



i wonder if it will stall at swla and setx????
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Quoting Felix2007:
Last time you guys started guaranteeing category 1 hurricane it wasn't, so what makes you guys so sure this time? Just curious.


This is the oh-so precious SFMR reading that the NHC was waiting on.
Member Since: July 15, 2006 Posts: 17 Comments: 10250
In a previous blog post, Dr. Masters noted that the ideal situation to break the drought in the U.S. would be a big, wet category 1 hurricane making landfall along the Gulf Coast. TS Isaac is the exact scenario that was described (only with slightly weaker winds!), yet this storm is certainly not being treated as a good thing. What gives?
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Quoting Felix2007:
Last time you guys started guaranteeing category 1 hurricane it wasn't, so what makes you guys so sure this time? Just curious.
Multiple readings of 105mph + Flight-level winds, along with 75+ mph SMFR estimates.
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Quoting Jstn568:
Only a few tropical storms have had lower pressures than Isaac:


(wind speed in kts)

Note: in the above list - most of the tropical storms recorded the given pressure/wind combinations over land - so it’s not quite an apples-to-apples comparison with Isaac.

(courtesy of this article)


While that info is helpful, we need a comparison to tropical storms over water that are intensifying prior to 1st landfall (or no landfall at all).
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RECCO still thinks 70 mph, but who cares?
Surface Wind Speed (likely by SFMR): 59 knots (~ 67.9mph)

NOAA dropsonde says hurricane - confirmed.
989mb (Surface) 135 (from the SE) 65 knots (75 mph)
962mb 155 (from the SSE) 93 knots (107 mph)
954mb 155 (from the SSE) 91 knots (105 mph)
942mb 155 (from the SSE) 95 knots (109 mph)
873mb 160 (from the SSE) 95 knots (109 mph)
850mb 165 (from the SSE) 91 knots (105 mph)
802mb 175 (from the S) 95 knots (109 mph)
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Quoting Felix2007:
Last time you guys started guaranteeing category 1 hurricane it wasn't, so what makes you guys so sure this time? Just curious.


It's hard to ignore multiple cases of 90 plus kts flight level in addition to 66kts surface.

It must be a hurricane now, especially with the radar presentation.
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Quoting Patrap:


Entergy's robo call said to expect 30 Hour's of Tropical Force winds with Outages expected to affect the Metro area and that would include Kenner and Metairie.


Welcome back...
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974MB now
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Isaac's remnants still hanging out there and giving much needed rain at 90 hours. And here comes Kirk.
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Quoting guygee:
The worst is yet to come...extreme inland flooding, the biggest killer for tropical systems.

Isaac has a really fat back end too.
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Quoting truecajun:
I am not liking THIS:

"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..."

"Category 2 Hurricane Gustav..." "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"

Their were LOTS of blue tarps and downed trees from Gustav. LOTS


Right... but Gustav had a smaller core of stronger winds. The destructive potential of Isaac's winds are not necessarily related to strength, but rather duration and area. An individual house has a better chance of faring well in Isaac - but because the possible number of houses that could be damaged are much greater, the damage level is higher.

Also, in regards to the duration, a well-built wood frame house can withstand 70mph winds under normal circumstances. But it puts strain on the house. The longer those winds blow, the greater the chance of that strain finding a fault in the construction, or just giving out.

The best analogy I can think of is when someone is water skiing... they can go all day at 25-30mph, but every once in a while, a unique combination of wakes and waves will cause them to fall. The longer they are going, the greater the chances are of that fall happening.
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Quoting GTcooliebai:
15:50:00Z 28.133N 87.583W 844.1 mb
(~ 24.93 inHg) 1,391 meters
(~ 4,564 feet) - - From 181° at 92 knots
(From the S at ~ 105.8 mph) 15.6°C*
(~ 60.1°F*) -* 94 knots
(~ 108.1 mph) 66 knots
(~ 75.9 mph) 21 mm/hr
(~ 0.83 in/hr) 64.6 knots (~ 74.3 mph)
Category One Hurricane


Getting real now.

By the time you adjust the top 4 models for the errors in their pressure initializations, they have done fairly well in intensity forecasting based on pressure for about the past 36 to 48 hours.

GFS has been the poorest on intensity overall, but for most runs since 2 days ago, it has been the best on track.
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105.8 mph
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We are 3 with one still in da rack here. I plan to nap at NOON CST, then get back in the saddle for the Big Show..later.

BigDuke NOLA 7

signing off..

Member Since: July 3, 2005 Posts: 424 Comments: 128314
The tornado threat with Isaac may be higher than normal for a landfalling tropical storm due to presence of all that mid-level dry air and the fact that since this storm's beginning, it seems, the mid-level center and the low-level center have never seemed to quite line up with each other. This should create much more directional shear between the low and mid-level vectors.

So the dry air allows more sunshine over land, increasing the low-level instability, feeder bands move through with their enhanced shear, more tornadoes result.
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GFS 96 hrs.

Member Since: August 31, 2009 Posts: 0 Comments: 5628
Last time you guys started guaranteeing category 1 hurricane it wasn't, so what makes you guys so sure this time? Just curious.
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are sandbags for only lowlying areas and neighborhoods that have a history of flooding?

we live in a newish neighborhood. we built about 6 years ago. we've never had problems with flooding. does that mean that we most likely will not with this storm??
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Enough with this.
Time: 15:51:00Z
Coordinates: 28.1167N 87.5333W
Acft. Static Air Press: 843.1 mb (~ 24.90 inHg)
Acft. Geopotential Hgt: 1,414 meters (~ 4,639 feet)
Extrap. Sfc. Press: 991.6 mb (~ 29.28 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 183° at 91 knots (From the S at ~ 104.6 mph)
Air Temp: 18.0°C* (~ 64.4°F*)
Dew Pt: 18.0°C* (~ 64.4°F*)
Peak (10s) Flt. Lvl. Wind: 93 knots (~ 106.9 mph)
SFMR Peak (10s) Sfc. Wind: 66 knots (~ 75.9 mph)
SFMR Rain Rate: 7 mm/hr (~ 0.28 in/hr)
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Quoting LostTomorrows:
I'm worried that they're missing something... I have never seen a tropical storm with a category 2hurricane's pressure in my life. The last storm I recall to have much lower pressure than winds was Irene, so what is this all about?
The worst is yet to come...extreme inland flooding, the biggest killer for tropical systems.
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64.6 knots (~ 74.3 mph)
Category One Hurricane

Flight level winds:
From 181° at 92 knots
(From the S at ~ 105.8 mph)

Height level: 844.1 mb
(~ 24.93 inHg)
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93HR new TD!!
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Quoting Chicklit:
From Moonlight Cowboy:
Sat presentation is better, looks like a duck, walks like duck, quacks like a duck, well...it's probably a duck! That's the way it needs to be treated. Isaac may sneak up on folks, 80 mph winds with higher gusts is no walk in the park.

I think you're right.

Isaac is a VERY serious storm still. It's lack of further classification has likely generated considerable apathy. Mistake. There will be very long periods of hurricane force winds on land. He will not be a "passing-thru" system. There will be lots of rain and flooding. And, there will be above estimated surge, imo, as well.

Right again. It's awful to say but am suspecting there will be deaths with this storm for the very reasons cited above.


There was no public awareness to be gained by upgrading now. That would have needed to be done at 5am this morning at the latest. It is too dangerous for people in SE LA to start trying to evacuate now...that would be a disaster waiting to happen.
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Quoting PlazaRed:

Pat wasn't there supposed to be some sort of an effect on storms that was going to be unpredictable,if the CO2 should ever get into the 400PPM bracket?
Or was that just some propaganda put out by alternative energy equipment manufactures, in order to increase sales!


Sea water characteristics may change as the partial pressure of CO2 continues to increase in the atmosphere. I wouldn't know exactly how this would effect hurricanes, but think of a soda bottle. When you open the cap the CO2 fizzes out of solution and escapes into the atmosphere. If a low pressure system was to pass over the ocean, something like that might happen and choke the storm with dry air, or maybe if the CO2 fills the eye itself, it absorbs more infrared from teh Sun and raises the core temperature...

Just two possibilities...


Which effect would be greater: Drier air from depressurized CO2 escaping the sea water in a low pressure system, or increased core temperature it may provide (during the day anyway)?


Those are some things I have thought of anyway,a dn there are others.

Higher CO2 will heat the oceans and boundary layer by a few degrees C, while cooling the Stratosphere by perhaps 5C to 10C, which means MUCH higher max thermodynamic potential for a hurricane.

Now some of the experts theorize shear should increase by the time AGW gets bad enough to produce these effects, so according to them, you will have fewer hurricanes, but when they do form some of them will be far more powerful than historical norms...

I think if you adjust the thermodynamic formula to account for these changes, you can get somewhere between 20mph and 40mph increase in max intensity for what is otherwise the same conditions... so that's anywhere from 1 to 2.5 categories, depending on where you already are on the SS scale...
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look what recon found

64.6 knots (~ 74.3 mph)
Category One Hurricane
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Hurricane Isaac...(surprise surprise)

Peak (10s) Flt. Lvl. Wind: 94 knots (~ 108.1 mph)
SFMR Peak (10s) Sfc. Wind: 66 knots (~ 75.9 mph)
Member Since: July 15, 2006 Posts: 17 Comments: 10250
15:50:00Z 28.133N 87.583W 844.1 mb
(~ 24.93 inHg) 1,391 meters
(~ 4,564 feet) - - From 181° at 92 knots
(From the S at ~ 105.8 mph) 15.6°C*
(~ 60.1°F*) -* 94 knots
(~ 108.1 mph) 66 knots
(~ 75.9 mph) 21 mm/hr
(~ 0.83 in/hr) 64.6 knots (~ 74.3 mph)
Category One Hurricane
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting Melagoo:
... Is Isaac a Hurricane or an imposter LOL
Poser....
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Quoting Gearsts:
But it was a major first.

Aaaah...I am glad someone dug that archive up....

It doesn't matter if it was a major first....its about pressure gradient the storm currently has. There are non-tropical storms with 965 mb that have max winds weaker than what TS Irene in NYC had...or what TS Isaac has now. Non-tropical systems are even more spread out than a tropical cyclone ever is...which makes for a lax pressure gradient (and more lax winds) for the same central pressure....

FYI Irene was becoming non-tropical when she headed toward NYC...as she interacted with an upper trough's divergence that spread the size of her low pressure field (and hence relaxed her pressure gradient). We see this more frequently than you think....
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127. landm
Quoting StormSurgeon:


I'm just over on Hillcrest/Grelot.


You are close and no rain?
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New Orleans
NEXRAD Radar

Base Reflectivity 0.50° Elevation
Range 248 NMI

Member Since: July 3, 2005 Posts: 424 Comments: 128314
Quoting WxLogic:
Dry air has been an issue with this system for quite sometime.
Always good to take a look at the big picture first as you could see right away what would be of hindrance to a developing system and go from there.
The dry air was not there all along, rather Isaac had an envelope too large for its own good. It was so large it kept sucking in the subsidence created by it own collapsing convection, and it could not spin up enough to mix that dry air out.

From my perspective on the FL east coast I got heavy rains both on the east and the west sides of Isaac. Most well-organized storms give me a good dose of subsidence on the west side, but not Isaac.
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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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