Isaac approaching hurricane strength

By: Angela Fritz , 9:14 PM GMT on August 27, 2012

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Isaac is walking the line of hurricane status this afternoon after a hurricane hunter mission investigated the storm and found winds of 80+ mph with the SFMR instrument, which looks down at the surface from the plane and estimates what wind speeds are. This instrument has a notoriously rough time in doing so when there's heavy rain, and since the strongest winds were recorded coinciding with the strongest rain, you can imagine that this region of high wind speed could be suspect. The hurricane hunter mission is still in the storm, so I imagine they will issue a special update if needed. Currently the best estimate of wind speed within the storm is 70 mph. Isaac's pressure has been dropping today as well and is now 981 mb. Isaac is moving northwest at 12 mph--no change since this morning. Satellite loops show that Isaac remains large, though asymmetric, with most of the strong thunderstorm activity on the west and southwest side. Isaac's southeast side continues to struggle with dry air and wind shear, which could help to moderate Isaac's intensity as it approaches the coast.

An oil platform in the northern Gulf of Mexico is reporting sustained winds from the north-northeast at 40 mph this afternoon. A buoy west of Tampa, Florida is recording sustained winds around 30 mph, and platforms south of Louisiana are recording winds from 35-40 mph. The widespread heavy rain of yesterday has lightened up in Florida, but a strong line of thunderstorms in one of Isaac's outer bands is training northward along and offshore of the east coast of Florida, affecting everyone from Miami to Jacksonville.

This afternoon the AP reported that Isaac's death toll in Haiti jumped to 19, which puts Isaac's total death count at 21. It appears most of the deaths in Haiti were due to collapsing structures.


Figure 1. Satellite imagery of Tropical Storm Isaac around 3pm EDT on Monday.

Track forecast:
Models seem to be coming into better agreement today on where Isaac will make landfall, closing in on Louisiana and New Orleans as most likely landfall point. The ECMWF, HWRF, and UKMET all suggest New Orleans as the landfall location. The GFS is only slightly west of that. The GFDL is the farthest west, predicting landfall near the Louisiana-Texas border. Landfall timing remains Tuesday night. Beyond landfall, Isaac is expected to move north toward the Midwest through the rest of this week, however, models are showing that the system will likely slow down around landfall time, prolonging impacts like surge and inland flooding.

Intensity forecast:
The closer Isaac gets to landfall without having formed an eye, the better it is for intensity at landfall. Isaac has strengthened only modestly in the past 24 hours, and is still struggling with a less-than-conducive atmospheric environment. The HWRF remains on the high end of the intensity spectrum, suggesting Isaac will be a weak category 2 upon landfall. Other models suggest it will be a strong category 1, but the difference is splitting hairs. The National Hurricane Center's official forecast is for Isaac to continue strengthening over the next day, reaching category 2 at landfall.


Figure 2. Tide gauge data from St. Petersburg, Florida. The green line shows the storm surge. As Isaac's counterclockwise winds blew offshore this morning, water levels feel two feet at St. Petersburg. The winds switched to onshore this afternoon as the center of Isaac moved more to the northwest, bringing a storm surge of two feet to the city.

Storm surge observations from Isaac
This morning, as Isaac's counter-clockwise winds brought offshore winds to the Tampa/St. Petersburg area, ocean waters fell two feet along the coast. This afternoon, winds have shifted to blow onshore, and a two foot storm surge has been observed at Naples, Fort Meyers, and St. Petersburg on the west coast of Florida. Water levels have also begun to rise along the coast of Louisiana, with a storm surge of 1.5 feet already occurring at Shell Beach on the east side of New Orleans in Lake Borgne.

Angela and Jeff

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Quoting HoustonTxGal:


I agree, I was just sharing it because it was interesting how it was done.


Yes, it was very interesting how it was done. Thanks for that.
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Quoting KEEPEROFTHEGATE:
..just look at itst size..when it comes ashore..it hits 3-4 states at one time lol...incredible how Large this system is, takes up 3/4 of the gulf, we were getting it in florida and the rain bands were reaching south carolina..wow
Member Since: August 6, 2011 Posts: 4 Comments: 36880
Quoting samiam1234:


seriously.. the storm is almost landing at the border of Louisiana/Miss.. its almost landing, every can see the north west projection.. and Texans are still thinking its coming for them.. guys come on this will not impact texas in any way...

Get a grip on yourself...you act like you have a magic ball and you know Exactly what this storm will do ...well guess what you don't ...THERE IS a possibility for Issac to go further west so chill out!!! May all stay safe in the path of Issac non matter where you are.
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Quoting allancalderini:
Washi Hanna will be coming in 2014 not 16.
Ah yes sorry for that mistake.Thanks :).
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550. ARiot
Mobile local news doing a good job explaining water surge potential.

Repost: NOLA and other gulf coast local coverage mix on Directv ch. 349. (No commercials :-)
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Quoting MississippiWx:
Isaac has an excellent outflow pattern and this will help him eliminate dry air issues eventually. You can see that the area east of him has gone from nearly cloudless earlier in the day to being mostly cloudy with bands of rain finally developing there.

Would be surprising if Isaac never becomes a hurricane.
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Quoting Pirate999:


12Z GFS run has landfall right on NOLA.

Although not impossible, it's doubtful that it would head west (famous last words).


I agree, I was just sharing it because it was interesting how it was done.
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546. wxmod
MODIS satellite photo today of churned up water off the Florida keys. Probably a large current flowing through there as Isaac pushes water in front of it.

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Quoting HoustonTxGal:


I believe he used the GFS for earlier today to create it.


12Z GFS run has landfall right on NOLA.

Although not impossible, it's doubtful that it would head west (famous last words).
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Quoting Dakster:
Next update, is Isaac a Cat 1 or not?


I doubt it. He may have slid back a bit pressure wise.

I would be surprised if a current vortex message still had eyewall values like it did a few hours ago.
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Quoting washingtonian115:
Gordon in 1994 was not taken off the list in.He killed 1000+.Hanna in 2008 killed 800 and as you can see will be back for 2016...
Washi Hanna will be coming in 2014 not 16.
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Quoting redwagon:

I don't see how can make any other landfall except Miss/Ala at noon tomorrow as a TS.
..if it does go into miss..then the panhandle of florida will also get those flooding rains, going to be one active day tomorrow in here huh
Member Since: August 6, 2011 Posts: 4 Comments: 36880
Quoting washingtonian115:
The models bombed Isaac out as a major.Didn't happen.This is why you must always be skeptical when it comes to models runs.Was entertaining to see what they did with Isaac though.


Isaac may just be nothing more than a 85 mph Cat. 1 in S. Florida we had much more intense storms and wind than when the center passed to out south.
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Quoting samiam1234:


seriously.. the storm is almost landing at the border of Louisiana/Miss.. its almost landing, every can see the north west projection.. and Texans are still thinking its coming for them.. guys come on this will not impact texas in any way...


I DID NOT CREATE IT... I was only sharing for those who might like to see it.. Trust me, I have o desire for the storm to come to TX.
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I see Isaac hasn't properly managed the dry air are mid levels. Good call on NHC on holding on that HURR declaration.... IMO.
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Isaac seems to be taking a jog North and is slowing considerably.

He is bottom heavy...needs to get the SW side to wrap around. Dry air!
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Is this even still possible?!?!
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Quoting weatherganny:

Do you think that is where Issac will go??


I believe he used the GFS for earlier today to create it.
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Quoting HoustonTxGal:
Here is an awesome WV image with the current NHC forecast and 15z WRF forecast overlaid




seriously.. the storm is almost landing at the border of Louisiana/Miss.. its almost landing, every can see the north west projection.. and Texans are still thinking its coming for them.. guys come on this will not impact texas in any way...
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Again Issac has problems.


URNT12 KWBC 272311
VORTEX DATA MESSAGE AL092012
A. 27/22:44:15Z
B. 26 deg 34 min N
086 deg 21 min W
C. 700 mb 2973 m
D. 48 kt
E. 139 deg 18 nm
F. 212 deg 70 kt
G. 132 deg 37 nm
H. EXTRAP 981 mb
I. 12 C / 3054 m
J. 16 C / 3073 m
K. 11 C / NA
L. POORLY DEFINED
M. NA
N. 12345 / 7
O. 1 / 1 nm
P. NOAA2 2809A ISAAC OB 19
MAX FL WIND 70 KT SE QUAD 22:34:49Z
MAX OUTBOUND FL WIND 52 KT NW QUAD 22:51:23Z
SLP EXTRAP FROM 10K FT
MAX FL TEMP 16 C 145 / 7 NM FROM FL CNTR
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Quoting Tazmanian:



nop


NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...700 PM CDT.
NEXT COMPLETE ADVISORY...1000 PM CDT

Taz:

7PM CDT= 8PM EDT.
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Quoting GTcooliebai:
Is that always the case with a storm that goes over Haiti that the government chooses not to call for retirement?


Not to sound bleak, but I think it's possibly because so much of the population is so poor, many probably don't even know the name of the storm (as in, probably don't have tv). Also, they would have to retire the name of a lot of storms being it's a likely scenario there that there will be a lot of loss. They don't even need an actual tropical system to cause a lot of loss.

Or, may just be the government doesn't care....or maybe some of both...
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Quoting HoustonTxGal:
Here is an awesome WV image with the current NHC forecast and 15z WRF forecast overlaid



Do you think that is where Issac will go??
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Quoting Tropicsweatherpr:


Invest 97L not developing opens the door for future 98L to go more west as the ridge expands.


And moisten things up for pre-98L to survive
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Product: NOAA Vortex Message (URNT12 KWBC)
Transmitted: 27th day of the month at 23:11Z
Aircraft: Lockheed WP-3D Orion (Reg. Num. N42RF)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 28
Observation Number: 19
A. Time of Center Fix: 27th day of the month at 22:44:15Z
B. Center Fix Coordinates: 26°34'N 86°21'W (26.5667N 86.35W)
B. Center Fix Location: 258 miles (415 km) to the WSW (248°) from Tampa, FL, USA.
C. Minimum Height at Standard Level: 2,973m (9,754ft) at 700mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 48kts (~ 55.2mph)
E. Location of the Estimated Maximum Surface Wind: 18 nautical miles (21 statute miles) to the SE (139°) of center fix
F. Maximum Flight Level Wind Inbound: From 212° at 70kts (From the SSW at ~ 80.6mph)
G. Location of Maximum Flight Level Wind Inbound: 37 nautical miles (43 statute miles) to the SE (132°) of center fix
H. Minimum Sea Level Pressure: 981mb (28.97 inHg) - Extrapolated
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 12°C (54°F) at a pressure alt. of 3,054m (10,020ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 16°C (61°F) at a pressure alt. of 3,073m (10,082ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 11°C (52°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Poorly Defined
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature
N. Fix Level: 700mb
O. Fix Determined By / Fix Level (Undecoded): 1 / 1 nm
Remarks Section - Remarks That Were Decoded...
Maximum Flight Level Wind: 70kts (~ 80.6mph) in the southeast quadrant at 22:34:49Z
Maximum Flight Level Wind Outbound: 52kts (~ 59.8mph) in the northwest quadrant at 22:51:23Z
Maximum Flight Level Temp: 16°C (61°F) which was observed 7 nautical miles to the SE (145°) from the flight level center
Remarks Section - Additional Remarks...
SLP EXTRAP FROM 10K F
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Looking a little ragged
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Good evening, geeks! ;) Y'all got this thing figured out?
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Isaac has an excellent outflow pattern and this will help him eliminate dry air issues eventually. You can see that the area east of him has gone from nearly cloudless earlier in the day to being mostly cloudy with bands of rain finally developing there.

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Wind Direction (WDIR):

NNW ( 330 deg true )

Wind Speed (WSPD):

25.3 kts

Wind Gust (GST):

31.1 kts

Wave Height (WVHT):

11.8 ft

Buoy 180nm South of Southwest Pass, Miss R.
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T/S Isaac is struggling again.


That's great. However, he's slowing down and that's not good.
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Anyone else over this storm? Hope all goes well in the gulf coast but this storm has been unimpressive from the beginning.
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Quoting HoustonTxGal:


A friend of mine has a friend with Water Decisions Technologies (WDT) he created the graphic to show the NHC projected path and water vapor.


Thanks! sure did get my attention. ;)
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Quoting Pirate999:
Interesting.. We are all concerned about NOLA (rightly so) and the flooding but it you look at where landfall is predicted, the bulk of the rain and surge will hit Mississippi and Alabama.
yes your right, and i have to warn you, that can be some real heavy rainfall there
Member Since: August 6, 2011 Posts: 4 Comments: 36880
Quoting Pirate999:
Interesting.. We are all concerned about NOLA (rightly so) and the flooding but it you look at where landfall is predicted, the bulk of the rain and surge will hit Mississippi and Alabama.


Thank you. Here in Alabama we are a tad bit concerned.
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So glad I put up boards now just makes me feel better for some reason

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Quoting airmet3:


Aircraft data is not supporting it.


Good to know... I would rather a strong TS hit than a Cat 1/2 Hurricane.
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Quoting Dakster:


I hope you are right... Because that would mean the levees in NOLA held up.
I've been hoping for that since the storm moved past FL. and all the models began to point towards them, 2 days ago it wasn't looking good and the HWRF had this storm blowing up into a Cat. 4 Hurricane and at the angle it is going in from the surge would have been a lot worst probably more than Katrina. Best case scenario is for Isaac to turn North towards Gulfport, make landfall and then do what it has to do to bring relief to drought in the Midwest.
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looks to me a bit of a jog to north oh well thats what they do
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Interesting.. We are all concerned about NOLA (rightly so) and the flooding but it you look at where landfall is predicted, the bulk of the rain and surge will hit Mississippi and Alabama.
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Quoting Dakster:
Next update, is Isaac a Cat 1 or not?


Aircraft data is not supporting an upgrade.
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Quoting Pirate999:


Where did that come from? The writting at the bottom was too small.


A friend of mine has a friend with Water Decisions Technologies (WDT) he created the graphic to show the NHC projected path and water vapor.
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Quoting Tazmanian:



not yet soon


I guess we find out either way in 43 minutes.
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Quoting MAweatherboy1:
He's in huge trouble now... Watch the last frame or two... convection has weakened significantly in the N/NE quadrant, worse than it already was... I think he's swallowed a ton of dry air... Anything more than a minimal hurricane seems unlikely to me now. Feel free to bash me, but that's what I'm seeing.



Well I agree, I mentioned it earlier and was going to mention it this afternoon but was afraid of getting bashed! But looks like a good swirl of dry was pulled right in to me too
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Very bad feeder band seems to approach Apalachicola Bay.

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Quoting Dakster:
Next update, is Isaac a Cat 1 or not?



not yet soon
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When a hurricane is this large, approaching any coastline that is not dead-flat will impede the circulation well before the center has a chance to get near the shore. Just as Katrina dropped from a 5 to a 3 as it approached the coast I would expect Isaac to weaken if it continues towards New Orleans.

Issac now might need to reach 975mb in order to reach category 1 strength, the area of circulation is so large. I think the only chance for Isaac to do this is if it stays slows and goes due west so that only the outer edges of the circulation will be affected.
Member Since: December 28, 2010 Posts: 0 Comments: 134
Next update, is Isaac a Cat 1 or not?
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Quoting washingtonian115:
Gordon in 1994 was not taken off the list in.He killed 1000+.Hanna in 2008 killed 800 and as you can see will be back for 2016...
Is that always the case with a storm that goes over Haiti that the government chooses not to call for retirement?
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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.