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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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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Quoting SirCane:


I agree GFS and GFDL was WAY out there with a TX/LA landfall.


The tracks are all the same its about the timing......
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1201. scott39
Guess where Jim Cantore is?......New Orleans......Guess where Isaacs center isnt going?.....New Orleans.....Lol
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If he blows up, it'll be now. His convection is continuously refiring, with new storms appearing to have begun firing to the west of the developing CDO. (two orange dots)



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Quoting nola70119:


By who? You?


No need to get snippy. I just posted models, I don't create their tracks.
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1198. sar2401
Quoting TomballTXPride:

That's the HPC ones, right? I just got done checking it out. Then yeah, those never pan on. LOL


Correct, the HPC models, which are almost never right, even with normal terrestrial storms, much less anything tropical.
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1197. Grothar
Quoting MississippiWx:


That's funny WX. You and I must have had the same thought at the same time. I mentioned this afternoon if anybody expected a shift changed and they acted like I.. well, I'll save that for later.
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Looks split in two pieces...

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Quoting SouthDadeFish:
And you base this seemingly very certain forecast upon??


He's related to StormTop.

Just kidding..
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1193. Dsntslp
Quoting Chicklit:
It would be really awful if the blob off the east coast turned around and headed back to south Florida.
Link WV Loop
UGH! :( Somebody who knows weather please, please tell me that is not possible, Please??
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Quoting TomballTXPride:


Poll?

A) Dry air

B) Eye


In that sat pic,the dry air actually looks like a knife point,sticking Isaac in it'd heart! Excellent Pic..
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1191. azduck
Quoting GetReal:



Isaac has ONE more chance and that is DMAX tonight. That will be his LAST chance...


Yeah, I agree with that, but even that is highly unlikely to be RI or anything like it.

Don't get me wrong, a serious rain event is seriously bad news for New Orleans. Lets hope the rain ends up somewhere with better drainage if that's what we're in for.
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Quoting Caner:


You know adblock plus is free, right?

;)


I do now, thank you
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1189. SirCane
Quoting MississippiWx:


GFS/GFDL are the only models remaining that show that track. Euro/Ukmet join the others.


I agree GFS and GFDL was WAY out there with a TX/LA landfall.
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Quoting MississippiWx:


Yep, pretty high confidence in Isaac making a landfall in close to the same spot as Katrina.


By who? You?
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1187. GetReal
Member Since: July 4, 2005 Posts: 204 Comments: 8896
Quoting osuwxguynew:
Good Evening Everyone!

Very impressive divergence is evident on the western side of Issac this evening.


Fairly strong easterly shear impacting the storm now, but looking at the the cimms shear, it appears that the expansive anti-cyclone is heading back toward Isaac now, as was suggested by the global models the past 24 hours.

CIMSS SHEAR


He'll struggle for another several hours, but he'll be undergoing RI late tonight into tomorrow afternoon up to landfall. Strong Cat 2 winds only likely despite a fairly low pressure (940s/950s). Going to be a rough day in Mississippi and eastern Lousiana...

And you base this seemingly very certain forecast upon??
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Quoting jake436:


OK, I clicked your link, I watched it loop several times, I sped it up, I slowed it down. So, what is occuring in that loop that would explain what's happening to Isaac right now? Serious question...
It was showing newly reformed convection firing on the northern side and a eye forming. And now we have a new eye and CDO forming.
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1184. MahFL
Isaac has excellent outflow on the SE and NW sides.
Member Since: June 9, 2004 Posts: 0 Comments: 3541
Quoting SirCane:
Shifting to Mississippi.



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.
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Quoting drj27:
Are the models starting to shift back to the east


Yep, pretty high confidence in Isaac making a landfall in close to the same spot as Katrina.
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Quoting nola70119:



GFS and GFDL are the only ones that matter...


GFS/GFDL are the only models remaining that show that track. Euro/Ukmet join the others.
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1180. Caner
Quoting Autistic2:



Every time I see a Muslim from Kenya I get sick. I don’t like being sick. I spent 10$ and suddenly I don’t see anyone like that anymore and I don’t get sick.

Maybe they are showing you what they know you don’t want to see to get the 10bucks?

Just asking



You know adblock plus is free, right?

;)
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1179. BtnTx
Quoting Walnut:
With Firefox and Ghostery I get no ads at all.
I pay my fair share subscription fee of $5/year as I am charter member. Look at my Member Since date. But even if I wasn't I would gladly pay $25/year as WU is worth it!
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1178. jake436
Quoting hurricanehunter27:
Good sat loop showing what is occurring with Isaac right now.

Link


OK, I clicked your link, I watched it loop several times, I sped it up, I slowed it down. So, what is occuring in that loop that would explain what's happening to Isaac right now? Serious question...
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1177. drj27
Quoting MississippiWx:
Are the models starting to shift back to the east
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Quoting Grothar:


Can I have a link to that ad?

All I get on here are ads for cemeteries and arthritis creams.


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
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1175. SirCane
Shifting to Mississippi.

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Even if Isaac remained a Tropical Storm, it would probably be the most damaging one since Tropical Storm Allison in 2001.
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Quoting gustavcane:
This was Bolaven on sat. when Upgraded to Category 1 Typhoon.



Now this is TS Isaac at this moment. Look familiar? he has the shape Typhoon Bolaven had.  He will be his twin if he can get that full round eye developed.




A little more goes into it than shape, lol, Bolaven had much more favorable conditions than Isaac.
Member Since: February 11, 2012 Posts: 83 Comments: 7834
Here comes the CDO. This looks like a very promising chance for Isaac if he want to make a serious attempt at Cat 2 or above.

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Quoting MississippiWx:



GFS and GFDL are the only ones that matter...
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1169. SirCane
Quoting sar2401:


Which models? Link? And don't tell me it's the UKMET.


Look at the ones MississippiWx just posted.
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Quoting waterskiman:

thats a bunch of bull, since the only lib site I frequent is this and all I get is Obama stuff.


And if you want to take it step further. The storm was around haiti and what was everyone talking about. Tampa Tampa Tampa, as if the storm was going to hit there full on when if you check out the thursday trak from the NHS which happened to be right by the by went no where near the freaking place
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Good Evening Everyone!

Very impressive divergence is evident on the western side of Issac this evening.


Fairly strong easterly shear impacting the storm now, but looking at the the cimms shear, it appears that the expansive anti-cyclone is heading back toward Isaac now, as was suggested by the global models the past 24 hours.

CIMSS SHEAR


He'll struggle for another several hours, but he'll be undergoing RI late tonight into tomorrow afternoon up to landfall. Strong Cat 2 winds only likely despite a fairly low pressure (940s/950s). Going to be a rough day in Mississippi and eastern Lousiana...

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This was Bolaven on sat. when Upgraded to Category 1 Typhoon.



Now this is TS Isaac at this moment. Look familiar? he has the shape Typhoon Bolaven had.  He will be his twin if he can get that full round eye developed.



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1165. Walnut
Quoting WXGulfBreeze:


With a paid subscription to support the site, I get no ads. ;-)
:)
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1164. vis0
Landfall over NOLA or just east as a strong TS or Cat1. Slowing and plenty of rain east of the storm (MS/AL).

Get a boat.. or floaties..
===================================
FIRST pay attention to REAL warning(s). IF i may just add a bit of levity as to the 3rd grade level:

A - Bewildering - Cat ??? - Doesn't - Elevate - From - Gusts to - Hurricane - Instead - Just a few - Knots below - Lallygagging - Mindlessly - Near - Orleans - Possibly - Questioning - Repeatedly - Should i - Turn - Up - Vastitude or just - Winds - Xanaduing with - Yynambus coloured edges - Zig zaging thru the gulf of Mexico (why i LIKED earlier comment ~ lets watch Issac Tango with Flo~.)

Know i know my ABCs won't you come and spin with me.
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Funny how cranky the blog is in the evening.

GO EAT, then come back.
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Quoting Ryuujin:
Possibly? Perhaps?


my guess is that it is an eye but clod tops and thunderstorms seem to have collapsed on the north side of the pin hole so it could be just dry air. HOWEVER, no one seems to be talking about how the center seems to be off track. I even just had one friend confirm that as not just me by stating that it looks like it is headed due north. I personally would guess Northwest.
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1161. Grothar
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Quoting HurricaneHunterJoe:
Im now watching New Orleans Coverage of Isaac. Thanks to whoever posted the Direct TV having the coverage on Channels 325 and 349.


Does anyone know if Dish Network is doing the same thing?
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Quoting TomballTXPride:

What's your thoughts, CCS? Been noticing you posting that same graphic now for about 5 times without any commentary. None to add? No problem. But would love to hear your thoughts on our buddy in the Gulf.



My guess is that Isaac will have a closed eyewall at 11pm Eastern
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1157. sar2401
Quoting SirCane:
Mississippi Landfall... Models showing that now.


Which models? Link? And don't tell me it's the UKMET.
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Quoting weatherh98:
Burst of convection on the north side is a very positive thing for the storm, negative for us


Yep, he's gonna make another run for an eyewall
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Quoting Chicklit:

Otherwise Isaac will be a big wet sloppy mess cruising into a Gulf coastal area and hanging around for days. What is worse?
I know. Sometimes the tropical storms that just hang for days cause the most damage.
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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.