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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Ok this may be old school but some time you need to go out side and just look up at the clouds. I am about a mile from the Gulf and in MHO I think he is moving NNW!
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...threshing wheat.
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All I can say is that, once again, Isaac is weird.
It has the pressure of a hurricane, the structure of a WPAC system and the annoyingness of Ernesto.
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Quoting BahaHurican:
Biloxi?
bwahahahaha
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Quoting BahaHurican:
Biloxi?


If I were a betting man, that would be my WAG.
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Being fed dry air at the mid-levels. Constantly being chopped, like thrashing wheat.
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1348. airmet3
Quoting Tango01:
I am tired of hearing CNN and now FOX talking about how similar Isaac and Katrina are. What do they have in common? One made landfall as a hurricane in FL, the other didn't. One hit the coast due north the other seems to hit it due NNW. One was a cat 5 a few hours before making landfall the other may end up being a strong cat 2 at the time of landfall. One will produce a storm surge at most of 18 ft, the other had storm surge of almost 30 ft. Again... what do they have in common other than the usual common characteristics with many other storms that hit the Gulf coast in the last several decades?


I agree 100%. Isaac has had near zero similarities to Katrina, yet that is all most anyone wants to use as comparison.
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Seems like Isaac winked at me again.
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Looking good Isaac.
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Quoting MZT:
Was just checking my mail box. A very dry, still, cool, moonlight night here in Charlotte. I can see from the images that the outer cirrus is only a few counties away in SC though


And I have cirrus over me and I'm over in Houston/Galveston area, that's a stretch from where you are and I am.
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Quoting CoastalAlabama:
I'm getting a bit tired of...

"...it looks like we are in an intensification stage right now..."

then...

"...it seems that there is an eyewall trying to form..."

then

"...dry air continues to be coming in from (pick a direction) and it's important to remember that it is not just all about the wind, but the length of time for the rain (or the size of the impact area means (pick a result))."

...on the Weather Channel.

Loved the Mobile Bay, Mississippi by Vivian earlier today...over and over...without any corrections from editors or producers in the earpiece. Doh!
We are now known as the Landmass between LA and AL!
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Quoting Chicklit:
Storm Junkie and PressLord are in Mobile; Cantore is in New Orleans. Guess we know where Isaac is probably going.
Biloxi?
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Quoting MississippiWx:


Just don't post the models and comment on where the majority of them point. ;-)


No problem here with data, you wrote "high confidence" without any explanation and that is a term the NHC uses and I associate it with their discussions.


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1341. angiest
Quoting GetReal:


Cirrus outflow now almost all the way to Corpus Christi.
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Video of Tropical Storm Isaac's affects on Siesta Beach on Siesta Key FL at 5:30pm todayIsaac's effects on Siesta Beach

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It's really kind of scary to see the forcasted storm surge, and yet the Mississippi Gaming Commission has not closed the casinos. These things sets right on the coast. What are they thinking (that's right, they're not!).
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1337. airmet3
Quoting wilburo33:


I was watching the New Orleans tv news radar and it shows the weakness on the north side due to dry air influx. This is a weak storm that may or may not make it to cat 1 status.
The biggest issue it is going to hit a city that is below sea level but the good news is that they now have competent leadership in place!
The former mayor, Ray Nagin is going before a grand jury soon for corruption while he was in office. Nagin was the mayor during Katrina.


I remember Katrina very well. It seems that NOLA may experience a pretty good storm surge with Isaac. How confident are the folks that the rebuilt levee system can withstand the influx of water?
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Quoting SirCane:


I remember Ivan 2004 and Dennis 2005 skirting to the East a bit just before landfall. Ivan was headed for Mobile and shifted to near the AL/FL line (Gulf Shores). Dennis was projected to Mobile Bay late in forecast and ended up 3 counties over in Santa Rosa County, FL. They don't always pinpoint the exact location.
That's why they have that cone that people so like to ignore...

:o/
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Flight level winds have crossed the hurricane threshold on the northern side of the circulation. Me thinks recon will find some 100 mph flight level winds on the south side.
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1334. Kumo
Quoting Chicklit:
Meanwhile, my son and his family are in South Korea expecting Bolaven. He thinks they're prepared.
It should be a CAT 1 at landfall.
And the 28th is his 28th birthday.
Lot goin on...sigh


I remember us getting some especially nasty monsoon rains during my tour there in '05-'08. Had a bit of flooding on post but it was nothing we could not deal with. Had about 1 Million USD in damage to the camp's golf course and club house, but that was about it. The Koreans and US Military are well prepared to deal with these events. I am sure that your folks will be fine. :)
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1333. KEEPEROFTHEGATE (Mod)
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I'm getting a bit tired of...

"...it looks like we are in an intensification stage right now..."

then...

"...it seems that there is an eyewall trying to form..."

then

"...dry air continues to be coming in from (pick a direction) and it's important to remember that it is not just all about the wind, but the length of time for the rain (or the size of the impact area means (pick a result))."

...on the Weather Channel.

Loved the Mobile Bay, Mississippi by Vivian earlier today...over and over...without any corrections from editors or producers in the earpiece. Doh!
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1330. Tango01
I am tired of hearing CNN and now FOX talking about how similar Isaac and Katrina are. What do they have in common? One made landfall as a hurricane in FL, the other didn't. One hit the coast due north the other seems to hit it due NNW. One was a cat 5 a few hours before making landfall the other may end up being a strong cat 2 at the time of landfall. One will produce a storm surge at most of 18 ft, the other had storm surge of almost 30 ft. Again... what do they have in common other than the usual common characteristics with many other storms that hit the Gulf coast in the last several decades?
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Quoting vis0:

On the contrary, when it was named Issac, NHC/others 1st 2 predictions were for Issac to head towards Mexico - Texas border(s) over a week ago. Then it was to head towards the Fla panhandle then we've got into a daily two step, i.e. one step east, two steps west


Link
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997.2 mb
(~ 29.45 inHg)
28.000N 88.133W

Estimated center as of 00UTC:
26.7°N 86.5°W
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Quoting waterskiman:

Not to give you a mouthful mate, but its blowing 70 pushing some good water into the gulf states that has no where to go but inland. and did I mention wind. Mate it was blowing 50 plus and I saw roof tiles blow off a neighbors house here in the keys.


Thanks mate, but lets keep things in perspective with respect to potential intensity.
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1326. MZT
Was just checking my mail box. A very dry, still, cool, moonlight night here in Charlotte. I can see from the images that the outer cirrus is only a few counties away in SC though
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Flight level winds of 65kts and still NW of the center and still in no convection. Surface winds at 47kts.
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Quoting TropicalBruce:
Issac reminds me of a Western Pacific tropical cyclone. Very large, with a barometric pressure lower then you'd expect for its sustained wind speed because of its size. The good thing is that any wind damage may be less than expected, but the bad things are the large water surge from the Gulf on the right side of it and the copious amounts of rain associated with this system.


IMO when the wind speed decides to catch up with the pressure we will end up with a strong Cat 1 not a weak cat 1 it will get there fast too.
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Ensembles saying....west again?? what on earth is this storm gonna do.
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Quoting sunlinepr:
Is he stalling? Almost looks that way. Or are my tired eyes deceiving me
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1321. GetReal
Member Since: July 4, 2005 Posts: 204 Comments: 8815
WOW, one of our Houston news reporters was interviewing the mayor of a city somewhere outside of NOLA live. Guy said that government picked and choosed and cherry picked projects due to costs and said he has NO CONFIDENCE IN THE FEDERAL GOVERNMENT of coming thru and even the levees holding up.
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Quoting TexNowNM:


You may be remembering Humberto. Went to sleep with a tropical storm and woke up with a hurricane. Humberto is a good example that it is water that kills the most. In Texas, only one person was killed by HURRICANE Humberto. An elderly man walked out onto his carport in Bridge City, Texas durring the storm and was killed when hit by something. TROPICAL STORM Allison which hit (or kind of took up residence in) SE Texas was responsible for over 40 deaths.



EXCELLENT point! Thanks! :)
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Quoting CaicosRetiredSailor:



We've a nice looking hurricane...on the south side! ;)
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1317. ThePass
At my house in Pass Christian, 2nd Street. Just walked down to parents (which is south of second). Very light winds almost calm. Will keep y'all posted as long as cableone is up lol
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@ Tristan... Wunderblog also has a forecast verification page for Isaac, accessible from the main tropical page.
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Quoting Nolehead:
wasnt it Ike a few years back off the coast of tx/la boarder that when we all went to bed it was a ts..woke up to a cat2 so anything is possible..parden me if i got the wrong name of the storm but you remember it..


You may be remembering Humberto. Went to sleep with a tropical storm and woke up with a hurricane. Humberto is a good example that it is water that kills the most. In Texas, only one person was killed by HURRICANE Humberto. An elderly man walked out onto his carport in Bridge City, Texas durring the storm and was killed when hit by something. TROPICAL STORM Allison which hit (or kind of took up residence in) SE Texas was responsible for over 40 deaths.
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Quoting scott39:
Isaac is building a shield around his center. Dry air is not going to keep him from strengthening.
We'll see about that... It's been plaguing him throughout his life so far...
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1313. vis0

Quoting sar2401:


Not a hurricane. He wasn't supposed to do a lot of things, including getting past 85W. So much for guessing.
========================
On the contrary, when it was named Issac, NHC/others 1st 2 predictions were for Issac to head towards Mexico - Texas border(s) over a week ago. Then it was to head towards the Fla panhandle then we've got into a daily two step, i.e. one step east, two steps west
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Quoting tristanh72:
Is there any site that keeps old nhc track images of previous storms? I'm curious to see going back how off the landfall line the tracks were this far out, and which direction they were off by.

Go to NHC's website, and look for Data Archive on the left margin.
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Quoting scott39:
I bet we got a hurricane...how about you?


Ehhh, I'll hold off on that one. LOL. :-)
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A few observations from Isaac: 1) Isaac reminds me that Florida is very fortunate that Hispaniola and Cuba are where they are. Without them I can foresee most storms hitting SE Fl at least two categories higher. When hurricane David hit many years ago, it was a 200 mph monster tempered by Hispaniola into a relatively tame 80mph storm. Once again these two countries kept a very large Isaac from spinning up.

2) Isaac was such a large storm that it has had a difficult time consolidating, especially, since it followed Saharan dust and relatively dry air.

3) Rainmakers can do lots of damage
4) forecasting intensity is still a (WAG) wild ass guess.
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Quoting LongIslandXpress38:
Looks like the Gulf Coast is going to dodge bullet only because our buddy Isaac couldn't get his act
together yesterday & is going to run out of time. If he had another 24 hrs. before landfall, I think we would be looking at a Cat. 3. Thank the gods for dry air..

Not to give you a mouthful mate, but its blowing 70 pushing some good water into the gulf states that has no where to go but inland. and did I mention wind. Mate it was blowing 50 plus and I saw roof tiles blow off a neighbors house here in the keys.
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The TWC just spoke to a person on the mission into Isaac. He says, Isaac looks better tonight than he has the past few nights. He is getting better and should be a hurricane tonight or 1ST thing tomorrow morning. It does look like he is trying again. Time will tell.
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1306. scott39
Quoting MississippiWx:
Recon is reporting 45kt winds and a 1001mb pressure well away from the center and in no convection.
I bet we got a hurricane...how about you?
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1305. WxLogic
Quoting SouthDadeFish:
Great analysis, thank you for sharing this.


No problem... :)
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1304. Reb74
Quoting treehuggingsister:


It IS lovely outside.

Not sure where you are but it is stifling compared to most nights lately. Absolutely "still" feeling even if the winds are not!
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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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