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 Stormchaser121:

Ensembles saying....west again?? what on earth is this storm gonna do.


He won't go back east. IMO, the landfall threshold now moves to a less likelihood of Mobile and is a bit further west. Just for saying sakes it takes a really strong storm to push up against 1016mb. Isaac has squeezed every inch it can up against 1012mb. See the SFC MAP - 1012mb is wrapped totally, almost in a circle around the storm, and it's still having trouble getting northwards, hence the slowed motion to 10 mph. Even if it strengthens a bit (and should, despite the dry air) it's still going to have a tough time getting ashore unless that shortwave trough trailing now over eTX further erodes the western periphery of the eConus ridge.

With Isaac's dry air/subsidence troubles on the northeast side he's only going to gradually strengthen having missed the warmer neast corner of the loop eddy. There's still a fair channel of warm water that runs swest to neast that should allow for some strengthening, but now I'm not thinking it'll be overly significant. We can't forget Humberto, but he was also much closer to shore (if I remember correctly), so there's still room, time for intensification; but, a 3 is likely not in the cards at this point.

Earlier I mentioned that this "stall" was beginning to concern me, having mentioned it yesterday too. If the plains high squeezes the swave trough and it lifts out to the neast or gets more lateral, we're looking at the makings of a blocking high northwards. Isaac could actually make landfall where it would eventually spin down, OR it could move back over open waters again. Not much chance of this I know, models probably not suggesting either, but I think it's possible. Call me crazy! ;)

Weaker is west, stronger is wnw, nw and then almost due north. Current motion at nw at 10 mph means Isaac is trying to escape, pushing as hard as he can, but he can't get there, so he'll creep westwards slowly, trying to put on some more armor and get poleward.

The circulation is too strong. And, he's trying harder to get symmetrical and vertical. Earlier this evening the MLC had broadened with the llc more intense for a change. The levels are getting symmetrical now, but the mlc and upwards are still a bit linear southwards. If that improves he'll be able to close off that neastern side and grow an eyewall. Lots of ifs!!!! ;P

With that vigorous a circulation and with no upwelling with slowing or stalling, I'm fairly confident Isaac will get to cane status and maybe to a low 2. He's going to slow even further, look for 5/6 mph at the next update or the next one.

The key bit here is still going to be surge (underestimated imo) and Isaac's strength to push poleward. A weaker, leveled off intensity storm will either weaken more and move further west, or it'll pop more northwards at the slightest bit of weakness that the shortwave trough may give it.

....slow, slow, slow deal developing
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Quoting Hurricanes101:
1509. AussieStorm 2:57 AM GMT on August 28, 2012
Carriere, Mississippi is going to get 16.92".

Question, how are they expecting that area to get 16.92 inches if they think the landfall will be in Louisiana; this is a west heavy cyclone. I would think the only shot Mississippi has at getting that kind of rainfall is if the system came in east of them


On shore flow. NE Quad has the strongest wind and the higher rainfall.
Btw, it's no me that is predicting that amount of rain, it's the HPC.
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1552. IndySuz
I'm too new to know how to post it, and I think it might break the copyright rules of the site anyway, but I laid the forecast track over the drought monitor map. I hate to think what this might do to the gulf coast, but once it's inland it's forecast to go over some areas that sorely need the rain.

(As one in an area that just finally got out of the "deep maroon" on the map, I appreciate rain more this year than I ever have. Water and burn bans just don't happen in Indiana!)
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24H 29/0000Z 29.1N 89.2W 80 KT 90 MPH...ON THE COAST
36H 29/1200Z 29.9N 90.1W 65 KT 75 MPH...INLAND
48H 30/0000Z 30.7N 90.7W 50 KT 60 MPH...INLAND
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Quoting txjac:



G'night ...bit first, what kind of animal is that you are holding in your avatar?

Ferral goat southern end of Aruba
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1549. jake436
Quoting oddspeed:
Katrina vs. Isaac:

KATRINA






Isaac




With that, you just put to bed the "similarities" between Katrina and Isaac...but I bet people will still be waking it up throughout the night...lol.
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Quoting MississippiWx:
A 979mb tropical storm. Lol. I've seen it all.

Life is now complete, I think the winds will respond soon though.
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1545. acl8610
Quoting fmhurricane2009:
Well... Isaac broke the record of being the 1st sub 980 millibar TROPICAL STORM EVER, it has a pressure of a strong category 1 hurricane.

Isaac is in DEEP thought right now, you get it? Because it is a Deep tropical cyclone?

Yeah, that was joke was about as bad as Jose (2010)

Is that actually true? first sub-980 Atlantic tropical storm
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1544. Dsntslp
The blob is dying out... :)

Link

Good night all.
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Not sure how much ya'll trust the long range GFS, I sure don't, but could we be looking at an Isaac CopyCat in the future?
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Quoting CoastalAlabama:



Alabama and Mississippi are often forgotten in the mainstream media. They are always seemingly New Orleans or the Florida Panhandle...we just fill the 'flyover state'. But this was really exposed following the Katrina aftermath, I think everyone could agree with that.

So this is rich:

Riddle me this... Channel 5 in Mobile:

"We are expecting to receive between 10-20 inches of rain"

then 60 seconds later:

"We have a 90% chance of rain Wednesday"


HAHAHA!!! C'mon. At least local Fox moments ago called for 100% rain Wed.


Hey don't say those 2 states, my comment on how you got the brunt of Katrina and not LA got my comment deleted by the mods.
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Quoting WXGulfBreeze:


Down by the port, it's decidedly UN-humid, but winds have picked up to maybe 20mph. Moon is ducking in and out of the clouds. Actually a nice night, though a bit on the breezy side. Only a few boats left in the marina.


It was cool as a cucumber around 6 this evening. Absolutely lovely.
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Quoting keno66:

First, we all know the dangers of where we live, so no one should need sympathy for a decision we consciously made. Second, I understand Mississippians "whining" because NOLA's disaster was truly "man-made." However, I can empathize with everyone who lost everything. We all had to pick ourselves up, dust ourselves off, and move on with our lives. With that being said, I apologize if my comment offended you.
NOLA's disaster was not totally man made. Without the levies, they still would have experienced considerable flooding. The damage was caused by the storm. Don't forget that though Katrina had cat 3 winds, the surge was like a cat 5 storm. This put extra strain on the levies. Moreover, a case could be made for "man made" causes of the MS losses too. I keep telling people, there's a reason why old-fashioned Bahamians didn't build their houses right on the beach. But you are right; there is no more or less suffering with this story. Everything I saw, very much secondhand, after the passage of Katrina, was horrendous and heart-wrenching. How much more difficult it must have been to experience firsthand that level of devastation.

I do think the media "ignored" the damage on the MS coast, because the NOLA story was so dramatic and, frankly, unprecedented. Additionally, the number of deaths there made for a morbid fascination. Finally, NOLA was relatively easily accessed. IIRC, it was literally days before outside help got to some parts of the MS coast.

I'm really gone with this post...
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Quoting fmhurricane2009:
Well... Isaac broke the record of being the 1st sub 980 millibar TROPICAL STORM EVER, it has a pressure of a strong category 1 hurricane.

Isaac is in DEEP thought right now, you get it? Because it is a Deep tropical cyclone?

Yeah, that was joke was about as bad as Jose (2010)

Wrong tropical storm Leslie of 2000 had winds of 70 mph and a pressure of 973mb
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Katrina vs. Isaac:

KATRINA






Isaac



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Quoting jake436:
Guys, Taz has been Taz here since long before I joined the blog. It used to drive me nuts too, but you get used to it. He's the resident...er...Taz. Take it with a grain of salt.

Ditto and double....I haven't been on here for a long long time but Taz is PART of this blog. Like if I were describing it I would have to throw him in....that's the atmosphere...it works.....it's where we come to get the real hurricane info.....
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1535. airmet3
I'm going to take one last dig at all of the Pasch Bashers from yesterday, because I can. If nothing else, I hope some folks have developed a little more respect for the fine folks in Miami.

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1534. acl8610
Quoting CloudGatherer:
The Air Force just registered 979.4MB - and it's flying at 5k feet, closer to the surface than NOAA. That'll be the level for the 11pm.

And a NOAA dropsonde in the southern eyewall just picked up 50kts at the surface - but 70kts a few hundred feet above it.

70 kts a few hundred feet agl... that should mix down to the surface soon if some more convection can get going
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-2mb in 3 hours, resuming the prior trend?

linear projection of -2mb per 3 hours would be -14mb from present offical, which is 965mb.

I adjusted the 18z GFDL and HWRF for their errors at present time and projected forward, and both were 963mb.

Adjusted landfall intensity predictors:

Adjusted GFDL 963mb
Adjusted HWRF 963mb
Linear Trend 965mb
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Quoting CoastalAlabama:



Alabama and Mississippi are often forgotten in the mainstream media. They are always seemingly New Orleans or the Florida Panhandle...we just fill the 'flyover state'. But this was really exposed following the Katrina aftermath, I think everyone could agree with that.

So this is rich:

Riddle me this... Channel 5 in Mobile:

"We are expecting to receive between 10-20 inches of rain"

then 60 seconds later:

I hope that I am the 10 percent that gets no rain!


I hope that I am the 10 percent that gets no rain!

"We have a 90% chance of rain Wednesday"


HAHAHA!!! C'mon. At least local Fox moments ago called for 100% rain Wed.



I hope that I am the 10 percent that gets not rain;)
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Quoting JLPR2:
Well no hurricane, but in other news, the EPac has a new TS.

...TROPICAL STORM ILEANA FORMS...NO THREAT TO LAND...
8:00 PM PDT Mon Aug 27
Location: 15.5°N 107.7°W
Moving: WNW at 12 mph
Min pressure: 1000 mb
Max sustained: 45 mph


I bet Ileana could make it to hurricane first than Isaac..what a shame.
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1530. IMA
Quoting gecko:


Did you totally log out and log back in again? It's been a while since I renewed but I thought that was in the instructions.
Thanks, y'all, but as a paid member since 2005 I really did try it all before I sent the first request for assistance -- banged my head on the wall; whined to the neighbor's cat about how I couldn't see more than 6 frames on local radar when we were getting our first storms in ages here in drought-stricken TX; logged out/in; logged out, closed browser, logged back in; logged out, cleared cookies, cleared cache, closed/re-opened browser; tried all other browsers -- not in that order, the head-banging & whining came later
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Quoting fmhurricane2009:
Well... Isaac broke the record of being the 1st sub 980 millibar TROPICAL STORM EVER, it has a pressure of a strong category 1 hurricane.

Isaac is in DEEP thought right now, you get it? Because it is a Deep tropical cyclone?

Yeah, that was joke was about as bad as Jose (2010)


should we make Jose the official worst looking crappy storm ever??
Member Since: April 23, 2011 Posts: 104 Comments: 14873
Off to bed.

Hurricane Isaac at sunrise IMO

G'nite

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1526. JLPR2
Well no hurricane, but in other news, the EPac has a new TS.

...TROPICAL STORM ILEANA FORMS...NO THREAT TO LAND...
8:00 PM PDT Mon Aug 27
Location: 15.5N 107.7W
Moving: WNW at 12 mph
Min pressure: 1000 mb
Max sustained: 45 mph

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1509. AussieStorm 2:57 AM GMT on August 28, 2012
Carriere, Mississippi is going to get 16.92".

Question, how are they expecting that area to get 16.92 inches if they think the landfall will be in Louisiana; this is a west heavy cyclone. I would think the only shot Mississippi has at getting that kind of rainfall is if the system came in east of them
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A 979mb tropical storm. Lol. I've seen it all.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Well... Isaac broke the record of being the 1st sub 980 millibar TROPICAL STORM EVER, it has a pressure of a strong category 1 hurricane.

Isaac is in DEEP thought right now, you get it? Because it is a Deep tropical cyclone?

Yeah, that was joke was about as bad as Jose (2010)
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979mb tropical storm. Western Pacific, anyone?
Well I'll call it a night. Isaac is weird.
Night everyone.
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Isaac 2012
The big storm that just couldn't.
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There is a potential for a flooding event being caused by the surge in the Tampa Bay. We are three hours before high tide and the water is about a foot from coming over the sea wall here in St Pete. Not sure what is going on with the water that is stacking up at the top of the bay. I will try to stay awake and give details as i know them. It is going to be close
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Quoting charlottefl:


That looks like a baby's head coming through the birth canal!!! As you were
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If these wildfield is tilted this way for landfall...lots of wind for long hours there in Nouvelle Orléans
Member Since: April 23, 2011 Posts: 104 Comments: 14873
980mb (28.94 inHg) Sea Level (Surface)
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1516. txjac
Quoting jake436:
Guys, Taz has been Taz here since long before I joined the blog. It used to drive me nuts too, but you get used to it. He's the resident...er...Taz. Take it with a grain of salt.


Know this sounds evil ...just cant do it
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Some of y'all act like you've never been on the Internet before. Unlike Isaac toughen up.
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Der ehrenwertest Grothar. Haben Sie irgendeinen Schaden oder Flutausgaben an Ihrem Ort gestern gehabt?
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1511. guygee
Quoting jake436:
I'm very familiar with Buras, and no doubt your area was demolished. However, "imagine driving into an area in which you spent 38 years and not knowing where you were because there weren't any recognizable landmarks"...you DO realize the same could be said for the entire MS coast, right?
I certainly do not want to make light of the destruction wrought by Katrina and the suffering caused, but how many of us at all could go to our birthplace and recognize anything? "Progress" wreaks its own kind of destruction...the long wars and the long ongoing depression have no end in sight.

A little of an old favorite song by the late John Hartford helps cheer me up when I think of these events:

Well the city's growing up where it looks all square
Like a crossword puzzle on the landscape
It looks like an electric shaver now
Where the courthouse used to be
The grass is all synthetic
And we don't know for sure about the food
The only thing we know for sure is them steamboat whistle blues
I'd sit and watch my TV if I thought I could trust the news
About the only thing I trust these days
Is them steamboat whistle blues


Good Night.
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1510. jake436
Quoting TomballTXPride:

Surprised that's been allowed to go on for so long.
Guys, Taz has been Taz here since long before I joined the blog. It used to drive me nuts too, but you get used to it. He's the resident...er...Taz. Take it with a grain of salt.
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Carriere, Mississippi is going to get 16.92".



Isaac will be known as a rain maker and not for his wind .
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fldude99 - you got mail!
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Quoting RitaEvac:
flag Taz's post, he'll be perma-banned for good, and never be back.


Rita, pls check your mail. Thanks!
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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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