Hurricane Isaac, Part 3 - Analysis and Forecasting Thread

[David Reimer]

IMHO, this caters to the point that we aren't going to have a very intense system...ie, a cat 1 cane.

Please correct me if I'm wrong, but how many systems do we see develop in a major cane over the shelf waters of the N GOM immediately prior to LF???

Again, I think a cat 2 is the realistic ceiling for this, with a cat 1 being much, much more likely.

Don't get me wrong, I don't see this becoming a major hurricane. I'm just saying don't be surprised to see a sudden uptick as it gets closer to the coast. Stewart mentions this in the 15Z advisory discussion. If the storm was strengthening while moving onshore, it would help winds transport to the surface more efficiently than a weakening or steady-state storm.

[David Reimer]

Product: Air Force Vortex Message (URNT12 KNHC)

Transmitted: 27th day of the month at 15:01Z

Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)

Storm Number & Year: 09L in 2012

Storm Name: Isaac (flight in the North Atlantic basin)

Mission Number: 25

Observation Number: 21

A. Time of Center Fix: 27th day of the month at 14:37:00Z

B. Center Fix Coordinates: 26°01'N 85°22'W (26.0167N 85.3667W)

B. Center Fix Location: 222 miles (357 km) between the WSW and W (259°) from Fort Myers, FL, USA.

C. Minimum Height at Standard Level: 1,334m (4,377ft) at 850mb

D. Estimated (by SFMR or visually) Maximum Surface Wind: 55kts (~ 63.3mph)

E. Location of the Estimated Maximum Surface Wind: 78 nautical miles (90 statute miles) to the NE (45°) of center fix

F. Maximum Flight Level Wind Inbound: From 123° at 47kts (From the ESE at ~ 54.1mph)

G. Location of Maximum Flight Level Wind Inbound: 56 nautical miles (64 statute miles) to the NE (45°) of center fix

H. Minimum Sea Level Pressure: 987mb (29.15 inHg)

I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 18°C (64°F) at a pressure alt. of 1,525m (5,003ft)

J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 22°C (72°F) at a pressure alt. of 1,529m (5,016ft)

K. Dewpoint Temp (collected at same location as temp inside eye): 18°C (64°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: 51kts (~ 58.7mph) in the northwest quadrant at 12:48:30

987 millibars with max SFMR at 55 knots in the latest VDM.

[40/70 Benchmark]

Don't get me wrong, I don't see this becoming a major hurricane. I'm just saying don't be surprised to see a sudden uptick as it gets closer to the coast. Stewart mentions this in the 15Z advisory discussion. If the storm was strengthening while moving onshore, it would help winds transport to the surface more efficiently than a weakening or steady-state storm.

Yes, I should have been clearer that I wasn't implying that was your stance.

I absolutely agree with the rest of this....I think its appropriate that one of the issues here is dry air because I have a feeling what most of us hobbyists, and pros alike, are going to be doing for the next 24 hours will be akin to watching paint dry in that "dry" air.....then as some of us are leaping from bridges, and proclaiming that all of this time was wasted on a mere TS...surprise, we have a solid little cane, who's track, angle of approach, area affected, and timing of intensification will be optimal for making this one of the most memorable "minimal" canes in history.

As a side note, I think it draws a parallel to Katrina's FIRST LF in that rergard....if you remember, it was a minimal can that was going to town upon LF in s FL.....very efficient translation of wind energy from aloft to the surface.

[Srain]

IMHO, this caters to the point that we aren't going to have a very intense system...ie, a cat 1 cane.

Please correct me if I'm wrong, but how many systems do we see develop in a major cane over the shelf waters of the N GOM immediately prior to LF???

Again, I think a cat 2 is the realistic ceiling for this, with a cat 1 being much, much more likely.

[40/70 Benchmark]

This image is a fail for me....what were you trying to illustrate?

[David Reimer]

Yes, I should have been clearer that I wasn't implying that was your stance.

I absolutely agree with the rest of this....I think its appropriate that one of the issues here is dry air because I have a feeling what most of us hobbyists, and pros alike, are going to be doing for the next 24 hours will be aking to watching paint dry in that "dry" air.....then as some of us are leaping from bridges, and proclaiming that all of this time was wasted on a mere TS...supprise, we have a solid little cane, who's track, angle of approach, area affected, and timing of intensification will be optimal for making this one of the most memorable "minimal" canes in history.

As a side not, I think it draws a parallel to Katrina's FIRST LF in that rergerd....if you remember, it was a minimal can that was going to town upon LF in s FL.....very efficient translation of wind energy from aloft to the surface.

Agreed. As I recall, most of New Orleans received at max around 100 MPH winds with Katrina making landfall. Most of the city didn't even receive that and wind damage was equivalent of a strong straight-line wind event out here in the plains. My concern is if Isaac is strengthening at landfall and does move fairly close to New Orleans, it could produce more wind damage than what some expect from a Category 1 because of the "lack" of wind damage from Katrina in New Orleans. Obviously Katrina also moved further east. In addition, we may also see more efficient transportation of stronger gusts to the surface which while not fitting the definition of a higher category hurricane, could prove to exacerbate the damage situation. Assuming NOLA does not evacuate, they could have a fairly high-impact event because of power loss and the associate failure of services.

That's just speculation and some observations in my opinion if we are dealing with a strengthening cyclone at landfall. Sustained winds may not increase much relative to a pressure drop before landfall, but the gusts may prove noteworthy. Overall, I still expect Isaac to be a fairly high impact event since it will be affecting a large population center.

[40/70 Benchmark]

Agreed. As I recall, most of New Orleans received at max around 100 MPH winds with Katrina making landfall. Most of the city didn't even receive that and wind damage was equivalent of a strong straight-line wind event out here in the plains. My concern is if Isaac is strengthening at landfall and does move fairly close to New Orleans, it could produce more wind damage than what some expect from a Category 1 because of the "lack" of wind damage from Katrina in New Orleans. Obviously Katrina also moved further east. In addition, we may also see more efficient transportation of stronger gusts to the surface which while not fitting the definition of a higher category hurricane, could prove to exacerbate the damage situation. Assuming NOLA does not evacuate, they could have a fairly high-impact event because of power loss and the associate failure of services.

That's just speculation and some observations in my opinion if we are dealing with a strengthening cyclone at landfall. Sustained winds may not increase much relative to a pressure drop before landfall, but the gusts may prove noteworthy. Overall, I still expect Isaac to be a fairly high impact event since it will be affecting a large population center.

Yes.

It really is a travesty that the percise LF intensity is obsessed over so much because its only one factor, albeit an important one.

There are a myriad of other factors at play here and there is a great risk posed if folks let there guard down because the hot blonde on the TV is only flaunting 2 digits, as opposed to 3.

How susceptible is the area being impacted? How largely populated is the area? What is the slope of the continental shelf just offshore from said area? At what angle is the system approaching the cost? Lastly, is the system intensifying, or decaying as it makes LF?

I think all five of those secondary factors that I have just outlined are going to work to accentuate the impact in this case, but the fact that the folks will only see 2 numbers next to the wind speed, as opposed to 3, may prove to be the most indirectly menacing factor of all.

[40/70 Benchmark]

One factor that could work in NO's favor as far as limiting wind damage, is that if this does indeed grind to a hault as it makes LF, then much of the wind energy may be expended over the relatively sparsely populated marshlands along the immediate LA coastline....the caveat being, that that would likely increase the threat of fresh water flooding, and allow more time for surge to pile up.

[dan11295]

The good news is any actual stall does not appear in the cards. A slow down to 5 mph will of course result in a lot of rain, but at least it will be moving.

[PSUBlizzicane2007]

Looks like the 12Z GFS shifts slightly to the right from a landfall SW of New Orleans at 06Z to a landfall S, almost SSE of New Orleans at 12Z. This isn't too surprising as the GFS and Euro (which should shift west) come more in line with each other between just west of New Orleans and Bay St. Louis.

[LakeEffectKing]

Loop this at http://wwwghcc.msfc.nasa.gov/GOES/goeseastconus.html

[Sunny and Warm]

Loop this at http://wwwghcc.msfc....seastconus.html

shallow shelf water showing the sand beneath?

[rcad1]

Looks like Hunters just found a 80 mph wind in the nw quadrant

[turtlehurricane]

Those are turbid continental shelf waters, the storm mixed up all the sediments and what not so it's opaque

[Baroclinic Zone]

Looks like the 12Z GFS shifts slightly to the right from a landfall SW of New Orleans at 06Z to a landfall S, almost SSE of New Orleans at 12Z. This isn't too surprising as the GFS and Euro (which should shift west) come more in line with each other between just west of New Orleans and Bay St. Louis.

I also have a hard time believing the 12z GFS slamming into that upper level ridge over the SW and not turning to the N.

[David Reimer]

Looks like the 403rd Wing based at Keesler Air Force Base (Hurricane Hunters) have relocated from Biloxi,MS and are now flying out of Houston, TX.

[Dunkman]

Looks like Hunters just found a 80 mph wind in the nw quadrant

Not seeing that unless you're talking about where it was raining 2in/hr in which case that seems like a lot of rain.

[PSUBlizzicane2007]

I also have a hard time believing the 12z GFS slamming into that upper level ridge over the SW and not turning to the N.

I've had a problem with that since 18Z Saturday considering the Euro and UK models completely disagreed. I think what is best is, as the NHC has mostly done, is just track it down the middle... and with the 12Z GFS shifting slightly to the east, it seems like that is the best bet at the moment.

[Sunny and Warm]

I also have a hard time believing the 12z GFS slamming into that upper level ridge over the SW and not turning to the N.

The experimental GFS enKF that LEK posted earlier seems a good track for Isaac. Coming N or NNW from directly south of NOLA, slowing down but not stopping for a day, and then continuing the north path through TN.

[Bruinsyear]

I think this storm will certainly put the levee's and pumps to the test since they have been rebuilt. They are only calling for 3-6 feet of surge but you get 15-20+ inches of rain and there are additional elements straining the system at Lake Ponch. Regardless of this storms strengthens beyond Cat 1. A long duration event with a continued fetch can be very problematic. Odd that it will almost make landfall the same day as Katrina (not trying to compare the storms by any stretch of the imagination).

[DopplerWx]

12z GFS still showing sig. strengthening tonight up until landfall.

[SmokeEater]

Not seeing that unless you're talking about where it was raining 2in/hr in which case that seems like a lot of rain.

TWC just said they found hurricane force winds in the NE quad.

[David Reimer]

TWC just said they found hurricane force winds in the NE quad.

We haven't had an aircraft in the northeast quadrant for over an hour now. In fact, I don't believe we have any aircraft in the system right now. We have two aircraft headed home with one just departing Houston.

[SACRUS]

Aside from when dry air and shear improve, Isaac's best chance for strengthening should be the next 10 hours and then prior to landfall over the best fuel conditions

[Dunkman]

TWC just said they found hurricane force winds in the NE quad.

There hasn't been a plane there in 90 minutes and the VDM from the last pass through the NE quad said 55 knots. I think one of the on air people probably tried to read recon data which is apparently beyond their field of expertise. There have been a few hurricane force SFMR readings but they were all heavily rain contaminated and did not jive with the flight level winds.

edit: Also, I've seen about enough of the erroneous TCHP map from 3 days ago. Can we agree to stop posting it?

[PSUBlizzicane2007]

Aside from when dry air and shear improve, Isaac's best chance for strengthening should be the next 10 hours and then prior to landfall over the best fuel conditions

That image is three days old.

[OSUmetstud]

Isaac has a more sheared look than the satellite analysis is depicting. I have to imagine that's either because of a) shear is found at a level that is being missed by GOES (perhaps 300-500mb) or the combination of modest shear and dry air entrainment.

[SACRUS]

That image is three days old.

Latest update i would expect those areas haven't changed much since Fri.

[DaculaWeather]

Based on the SPC meso-analysis, it appears the ridge to the east over the Carolinas and Georgia will be relaxing over the next 4-6 hours, but what that means for track changes I'll leave to the mets here.

[Msalgado]

I don't think there's much of a chance for strengthening based on those TCHP plots. While people see slivers of warmer water, I see a real lack of TCHP that we usually see in this area of the Gulf and a large system that will be encouraging a large amount of upwelling.