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 sunlinepr:
Looks split in two pieces...


haarp
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1253. Caner
current microwave, still a beeline for just south of New Orleans:

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1252. bappit
Isaac looks peaked. (pee' kd)
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1251. WxLogic
OK... back to PC ( at least for a bit ). Was checking out the moisture levels vs dry air and we still have dry air issues being pretty much enhanced by land (in this case CONUS).

Below you'll see that there's an area of quite pronounced drying to the NE of Isaac at around 400/500MB:



Also noticed that below the 500MB level, at 600MB there's more dry air but appear to be a thing layer.

This falls quite in line with the latest RAOB obs from KTBW:



I'll continue to expect Isaac to be at a border line TS/HURR like earlier until is able to manage this dry air accordingly. Almost had it earlier today but convection collapsed prematurely due to an intake of dry air. As discussed before.

On a side note... the more Isaac delays on moving quick enough the more time it gives the steering currents a chance at changing in configuration and therefore the path.
Member Since: August 14, 2008 Posts: 4 Comments: 4932
Quoting nola70119:


Katrina came ashore at Grand Isle, not Mississippi.



Lol. Actually it was Buras. Grand Isle is further west. Katrina made its third and final landfall in Mississippi at Bay St. Louis. I know this very well.
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Here's a nice little radar loop that shows clearly that Isaac is sucking in dry air. For having a TS right offshore, Pensacola is unusually un-humid tonight.

Link
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Quoting SirCane:


Bottom line this is not an exact science. Take responsibilty for your own safety.
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1247. scott39
What we have to remember with Isaacs landfall, that Al/MS/LA arent that far apart. Any variation in track could easily have Isaac make landfall in any of those states.
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Katrina track...mississippi bound...some of you say it won't make a difference it is still close to NO...b.s.....makes a big difference...i ain't afraid to tell you how it is going to be...unlike these meteo clowns on TV....all saying the same thing when water vapor shows a totally different story...
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If the Mississippi coast is affected, please consider helping out through the Back Bay Mission in Biloxi. Not taking anything away from Portlight, but Back Bay is a Biloxi institution and is always there helping those in the Gulfport-Biloxi area who lack the means to recover from disasters - natural and man-made.
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Quoting GetReal:



LOL which was Buras, La.... Just to be accurate.


Yep. Buras, then another landfall in Bay St. Louis, MS.
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Quoting MississippiWx:


Ok, I said pretty high confidence that Isaac will make landfall near the location of Katrina. Guess where "near" would be? New Orleans. You are reading way too much into this...


Katrina came ashore at Grand Isle or Buras, not Mississippi.

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1242. Walnut
Quoting CosmicEvents:
Is there anyone here who saw the last piece on TWC with the hurricane hunter crewman(pilot?). I was watching in the background but it seemed like he was bullish about this storm. And it wasn't Cpt. Reed.
Saw it and agree with your take on what he said.
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Quoting Elena85Vet:
FWIW

Paul Flaherty (Aboard Hurricane Hunter) says Isaac is more organized than he's been in three night's.

"Flight level center is closer to the surface center than it has been"





What altitude is the flight level?
Member Since: August 29, 2008 Posts: 0 Comments: 455
1240. SirCane
Quoting nola70119:


The MS/LA border is 20 minutes from my house......thats Louisiana.


I don't know what point you are trying to make with people here. I'm just pointing out that the models have shifted a bit to the East.
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Quoting Dsntslp:
UGH! :( Somebody who knows weather please, please tell me that is not possible, Please??
omg don't SAY things like that!! EDIT: oops! meant to quote Chicklit's original comment, not your response lol
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Gas stations running out of gas here.

New cartoon on facebook here:
You think shopping for Black Friday is bad? You've clearly never shopped at Walmart before a hurricane!
Member Since: August 22, 2009 Posts: 0 Comments: 3115
Quoting bixms:
A Mobile hit (sorry Mobile...) would be great for me as I am not prepared for a south wind (NO hit). No ill will meant for anyone.


Why are you not prepared for a south wind? The forecast track has had this mostly west of the Mississippi coast for a while now. That means southerly winds.
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Thanks for the answer^^^^
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Hurricane Hunters were just on TWC saying that the low level circulation and mid level circulation are extremely close to being vertically stacked this evening which is something they have not seen until tonight and they expect quick strengthening once that happens.
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FWIW

Paul Flaherty (Aboard Hurricane Hunter) says Isaac is more organized than he's been in three night's.

"Flight level center is closer to the surface center than it has been"



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Storm Junkie and PressLord are in Mobile; Cantore is in New Orleans. Guess we know where Isaac is probably going.
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1231. GetReal
Quoting MississippiWx:


Ok, I said pretty high confidence that Isaac will make landfall near the location of Katrina. Guess where "near" would be? New Orleans. You are reading way too much into this...



LOL which was Buras, La.... Just to be accurate while splitting hairs..
Member Since: July 4, 2005 Posts: 204 Comments: 8806
1230. 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 you go with the cone.
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1228. bixms
A Mobile hit (sorry Mobile...) would be great for me as I am not prepared for a south wind (NO hit). No ill will meant for anyone.
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1227. MahFL
Quoting scott39:
Guess where Jim Cantore is?......New Orleans......Guess where Isaacs center isnt going?.....New Orleans.....Lol


It's going to hook right to Biloxi for sure!
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1226. MahFL
Hmmm, peoples lives are about to be ruined and TWC cuts short a live interview with the HH because "they ran out of time". Hello ? did time stop ????
I drives me mad.
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Quoting SirCane:


They go with the TVCN which is an average of the models now at the MS/LA border. Watch and see.


The MS/LA border is 20 minutes from my house......thats Louisiana.
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1224. SirCane
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.



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.
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For those downplaying the heat content available to Isaac, they just have to look at where Gordon went from a tropical storm to a strong Cat 2 (possibly post season upgrade to Cat 3).

See above and east of 30N 50W in this TCHP map. Certainly more available in the Gulf on its future track according to SHIPS...


Also, while outflow was good in all quadrants for Gordon, it did not have quite the outflow channels that Isaac does to rapidly remove mass from the eyewall that will form.


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1221. sar2401
Quoting Dsntslp:
UGH! :( Somebody who knows weather please, please tell me that is not possible, Please??


It doesn't look possible to me. It's moving NNW and trying to nose into Georgia while trying to fight off all the dry air around it.
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Quoting nola70119:


You mean you just post models and say "high confidence"?


Ok, I said pretty high confidence that Isaac will make landfall near the location of Katrina. Guess where "near" would be? New Orleans. You are reading way too much into this...
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1219. Walnut
Quoting SirCane:


They go with the TVCN which is an average of the models now at the MS/LA border. Watch and see.
Yeah it now looks like a clear path in steering to the north now. Hurricane Hunters are saying on TWC that storm likely will be a cane tonight and is getting better organized. Guess we will see.
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1218. kjcanon
Quoting dogsgomoo:
Ah. Is it the phase of Hurricane formation where we start posting "science" articles from 100% tabloid newspapers in order to prove why the storm isn't doing what we think it should be doing?

Cool.

Personally, I think it's all Prince Harry's fault. He didn't keep what happens in Vegas in Vegas. Due to uncontrolled global exposure to crown jewels all that overwhelming dry cheeky British humor has affected Sir Isaac's NE quadrant.


Priceless.... I vote this "post of the season".
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IMO, Isaac will get picked up by the cold front and move more nne and ne...katrina track with last minute shift to east....watch out mississippi
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Issac has been pretty lopsided for some time now. Cuba prevented full development in the S-SW quadrant (too close to Cuba), his Eastern flank was having trouble earlier today (perhaps too close to Florida), and now his Northern flank has been having problems (nearing landfall in the Northern Gulf)......I am starting to see a pattern here............Big storm/big circulation and not enough room to fully pull it together.
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Quoting gulfbreeze:
He has slowed down to 10mph. Could be about to stall or change direction .Models do seem to be going back to the east. Wind here is p/u.


What does p/u mean?
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Quoting airmet3:


The center is right on the edge of the Northwest Florida radar. Not sure which radar you are using.

NW Florida is shooting through the dry air on the north side, but the mid level circulation is there and has at least some scattered convection.


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.
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1213. Grothar
Quoting mitthbevnuruodo:


hahaha well, I'm wary to click it for you in case it just infects me with a virus! You seem to be doing alright on you own ;) the other main ads I get is for some clothing store called zulily...maybe that'd be good for you?! LOL All lost on me as I have no money to spend these days on anyone selling anything anyway LOL

Aren't you supposed to be on vacation?! the hope of looking years younger making you break out of vacation mode?! LOL


No, I am not on vacation. My family is away for awhile.

I am usually a paid member, but this year when I went to go on PayPal, I got a message that read "Expired". At first I wasn't sure they meant me or the account. I will try again this week.
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Quoting SouthDadeFish:
And you base this seemingly very certain forecast upon??

That shear map is from 9 a.m. this morning (1500UTC).
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OK...we're all set. Gonna have a crew (including 2 EMT's) at the Biloxi Special Needs Shelter from tomorrow morning until the storm passes. They will be caring for shelter dwellers, as well as assisting with evacuations. They will also be doing rescues of people who call for help.

Another team will be surveying all the shelters in the area to ensure that they are accessible to all people.

John Wilbanks will be hunkered down in a Biloxi parking garage live streaming video. He's gonna be able to give great real time, on scene reports.

Wednesday we will begin doing needs assessments and start to engage in the relief phase of our work.
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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..
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Quoting MississippiWx:


No need to get snippy. I just posted models, I don't create their tracks.


You mean you just post models and say "high confidence"?
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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.

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1206. SirCane
Quoting nola70119:


Really.....that GFS has been where it is for two days. When it shifts lets talk. And the GFDL is with it. Besides the NHC is now using other tools to determine track, not just the models.


They go with the TVCN which is an average of the models now at the MS/LA border. Watch and see.
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He has slowed down to 10mph. Could be about to stall or change direction .Models do seem to be going back to the east. Wind here is p/u.
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Very high winds (30+ at times on the bluffs above Pensacola Bay). Almost no rain. I was surprised at the wind strength. Just a few blocks in from the bay I'd say winds are 5-10 MPH.
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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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