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 LargoFl:
GFS at 252 hours..oh oh...........


.....sooooo we'll get isaac landfalling and follow until dissipated and then start it all over again.
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377. GTcooliebai 10:42 PM GMT on August 27, 2012 +0
300 hrs. I think Kirk has the best chance to become this season's first Major Hurricane, which is kind of amazing we haven't gotten one yet.


Let's see: Storm Chance of being first major
Alberto 0%
Beryl 0%
Chris 0%
Debby 0%
Ernesto 0%
Florence 0%
Gordon 0%
Helene 0%
Isaac .00005%?
Joyce 0%
Kirk .0001%?

Yes, I guess that, so far, Kirk has the highest probability of becoming the season's first major hurricane. Congratulations.
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Quoting JLPR2:


Not necessarily, the GFS closes 97L off, it just doesn't deepen it much, but considering it still has an anticyclone on top of it and a good circulation, it could try.

It's possible but unlikely... the center is nowhere close to the convection.

By the way I just looked at the vis. loop of 97L and it is so cool! Watch the two little circulations rotate around each other, especially in the first half of the loop before darkness.

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451. FOREX
Quoting Charmeck:

That would in 65 minutes - it is 7:00 PM Central Time!


it is 6pm central right now.
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GFS at 252 hours..oh oh...........
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Quoting STXHurricanes2012:
I believe Isaac just moved into Central Daylight Time zone!


Well, the NHC has been using CDT for their advisories now for a while.
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Quoting Tazmanian:
the 7pm update is comeing out any time

That would in 65 minutes - it is 7:00 PM Central Time!
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Conditions at 42003 as of
(4:50 pm CDT)
2150 GMT on 08/27/2012:
Wind Direction (WDIR):

SW ( 220 deg true )
Wind Speed (WSPD):
42.7 kts
Wind Gust (GST):
56.3 kts
Wave Height (WVHT):

16.1 ft
Atmospheric Pressure (PRES):
29.22 in
Pressure Tendency (PTDY):

+0.09 in ( Rising Rapidly )
Air Temperature (ATMP):

79.5 °F
Water Temperature (WTMP):

84.9 °F
Wind Speed at 10 meters (WSPD10M):

46.6 kts
Wind Speed at 20 meters (WSPD20M):

48.6 kts




Buoy 208 nm West of Naples FL
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445. JLPR2
Quoting MAweatherboy1:
I think we can safely RIP 97L.



Future 98L will probably officially be declared 98L tomorrow or Wednesday, I believe that is the one the models are making Kirk.


Not necessarily, the GFS closes 97L off, it just doesn't deepen it much, but considering it still has an anticyclone on top of it and a good circulation, it could try.
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Quoting CaicosRetiredSailor:
Time to change this storm's name

to

saac

He just NEVER has an "I"
Love it!
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I believe Isaac just moved into Central Daylight Time zone!
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Quoting KEEPEROFTHEGATE:
only a few vis frames to go till darkness falls



Seems like it's exploding around the center.
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Quoting SFLweatherBen:
Flooding in Broward County worse than I thought it would be.

..good pic there ty..i dont think anyone ever knew east florida would get hit so bad as it did today..all that was supposed to be what we here on the gulf side were expecting, im lucky if i got a whopping 2-3 inches of rain today..we will see once the totals come in
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Quoting Chucktown:


Peak of the hurricane season is in 2 weeks. The African wave train is probably at its peak right now.
Ok.
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438. FOREX
Quoting GTcooliebai:
300 hrs. I think Kirk has the best chance to become this season's first Major Hurricane, which is kind of amazing we haven't gotten one yet.



How do you see the GFS? The site that I use it shows it hasn'rt run yet.
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only a few vis frames to go till darkness falls

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Quoting CaneHunter031472:


Well, the peak of the season is still about a month ahead, but I can only hope we do not...


Peak of the hurricane season is in 2 weeks. The African wave train is probably at its peak right now.
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to me in that last few frames looks like it may have taken a N jog..living just n/o orange beach, al we aren't taken our eyes off this crazy storm just yet..
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It is rather nice here in Fort Walton right now. Winds blowing 5-10 with smattering of rain. I think we are experiencing the part of the rotation with the dry air. Looking at the sattelite I wonder if we will get much rain here afterall.
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Quoting Stormy2day:
anyone think the current track is too far west? What are the chances that this stalls and strengthens?


Chances are huge. Gfs shows it as well as the euro, but I rather stick to the official forecast.
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._.
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Quoting Tazmanian:




ugh there uesing CDT


Yeah, I got confused earlier, too.
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Quoting Thing342:
8pm EST.



nop


NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...700 PM CDT.
NEXT COMPLETE ADVISORY...1000 PM CDT
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Quoting CaneHunter031472:


Actually I think she's about to get rid of that dry air. It does look a bit elongated tho.

I think Isaac made himself too big, which makes him susceptible to the environment around him, so he draws in dry air.
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Anyone else seeing the fact that the storm has been moving due North... long wobble.
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or maybe

I(less)saac
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Quoting angelafritz:
Has anyone else noticed that I struggle most with simple figures of speech? First, it was the elbow of Florida. Now it's pulling hairs. :)
You're doing fine. Thank you.
I recall my then fiancees first dinner/meeting with family when she jumbled her words regarding preferring one part of calamari to another. She swung and missed on tentacles.
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Quoting Hurricane12:


That would be in nearly an hour, I believe.




ugh there uesing CDT
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Quoting TomballTXPride:
Well, HWRF started out reasonable, but then bombed it out again between 18 and 24 hours. Subtract the difference to account for the bad initialization and it's still suggested IR and a VERY strong hurricane. Not buying it though. Really not.



I know it seems weird, but it's about right at the present linear rate of 1mb per hour, infact, if you add the 11 or 12 back, it's 964mb.


Right now the real storm is 981mb as of 4pm central.

It's supposedly going to hit plaquemines in 21 hours.

981mb - (1mb/hr * 21hrs) = 960mb


It's still realistic, because it's been following that rate all day long...
Member Since: January 25, 2012 Posts: 33 Comments: 1520
anyone think the current track is too far west? What are the chances that this stalls and strengthens?
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Quoting Tazmanian:
the 7pm update is comeing out any time
8pm EST.
Member Since: August 1, 2012 Posts: 0 Comments: 441
Quoting Tazmanian:
the 7pm update is comeing out any time


That would be in nearly an hour, I believe.
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Quoting SFLweatherBen:
Flooding in Broward County worse than I thought it would be.



Stay safe.
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the 7pm update is comeing out any time
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Quoting TropicalAnalystwx13:
I'm still holding onto my thought that the USA will be impacted by a major hurricane this season. Ernesto missed it by four days. Isaac will likely miss it due to dry air. It seems we're getting closer though (unfortunately) as we head farther into the season.
Well I'm up for a chase. Isaac is too far away. Anywhere on the FL. peninsula East or West Coast I'm willing to go should a hurricane be bearing down on it this season.
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I think we can safely RIP 97L.



Future 98L will probably officially be declared 98L tomorrow or Wednesday, I believe that is the one the models are making Kirk.
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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.

Quoting RTSplayer:
We probably have a closed eye now.

It went from dry slot to a hot tower over the former dry slot within about a 1 hour time frame.


Crazy storm has been deepening about 1mb per hour all day long, so at that rate it could shed another 24 to 30 or more mb before landfall.

If you correct the HWRF by 11mb to fix the bad initialization, you get 957mb at land fall.

If you subtract one millibar per hour between now and the official forecast landfall, you'd get 961mb at lower plaquemines and about 940mb at NOLA, since the model actually says it will keep intensifying for a few hours after passing Plaquemines. So basically split the difference on that, and you'd still maybe have 950mb at NOLA coordinates, and this ends up in the same ballpark as the model itself.

Overall, HWRF may be doing a good job on intensity, it just started out a tad too strong.


GFDL is about 3 to 6 mb too high, so we need to subtract that from the results, giving 960 to 963mb as it approaches landfall on the other side of the state.


Of course, those model runs are about to update, so we'll see if they corrected their mistakes and had better initializations this time around.

Anyway, reality has not been too far behind HWRF's rate of intensification once you correct for the bad inititialization, indeed, reality has actually beaten the average rate of intensification of the HWRF...


This say's it all. LMAO

It has been cycling LLC's with dry air for 5 day's now. Today will be no different. Still enough going on to reach CAT 1 but that's about it.
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Quoting blsealevel:


yea I just hope it dont get any stronger but a slight stall and here we go :)


Memories of Allison flooding Houston. That's not what NOLA needs. Slowing down and no intensification could be just as bad as a cat2 (or worse)
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Flooding in Broward County worse than I thought it would be.

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Quoting GetReal:


Funny HH just found 65+kt winds n the NE Quad....



Remember this is flight level winds. They are flying at about 4,800 feet.
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So is a more dominate westerly track being ruled out now?
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Time to change this storm's name

to

saac

He just NEVER has an "I"
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Quoting TropicalAnalystwx13:
I'm still holding onto my thought that the USA will be impacted by a major hurricane this season. Ernesto missed it by four days. Isaac will likely miss it due to dry air. It seems we're getting closer though (unfortunately) as we head farther into the season.


Well, the peak of the season is still about a month ahead, but I can only hope we do not...
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Quoting Hurricane12:


It's a pretty nice consensus.


yea I just hope it dont get any stronger but a slight stall and here we go :)
Member Since: August 23, 2008 Posts: 0 Comments: 1918
Quoting LargoFl:
GFS at 336 hours..storm #3


Quite a bit can happen in 2 weeks. Good to see models but I'm a skeptic. As Dr. Neil said, when it gets to the islands we'll start to watch.
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Quoting GetReal:



Has anyone on the blog currently ever seen an ATL TS, in the month of August or Sept, with a 981mb pressure reading that wasn't a strong Cat 1, or low end Cat 2???

I know that I haven't until today, after 40 years of observing ATL storms.


Yes it is rather fascinating, however anything is possible with mother nature. I think this year more than ever we have seen that.
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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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