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 hurrtracker1994:


There isn't any indication from recon that we are there yet. I would agree we are close to a hurricane, but we are not there yet.



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.
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Quoting MAweatherboy1:

I think Kirk (or whatever name this storm gets) will be a big one... You never see so many models on board for development this early on.


Kirk could be pretty bad and that wave definitely needs to be watched. GFS also shows Isaac bringing me some rain which would be good.
Member Since: March 16, 2012 Posts: 127 Comments: 7981
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Quoting Fishinnfever05:
Man there is a lot of activity from mobile tonight. I am here off of cottage hill!

Do you. Think we will really get that much rain?


I have no idea.
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looks like its calming down some in florida, just cells of rain coming in around here..isolated not like over on the east coast, local weather met said for the next 2 days this is what we can expect..sun then rain,sun then rain etc
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Quoting washingtonian115:
I don't think Isaac will go through RI.


In the immediate future I definitely agree. There are just too many factors going against Isaac that will impede RI from occurring.
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Pressure has leveled off for now, a consistent 981-982mb.
Member Since: March 16, 2012 Posts: 127 Comments: 7981
Central Louisiana here! Going to setup live video, if possible. 
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Quoting Fishinnfever05:
Man there is a lot of activity from mobile tonight. I am here off of cottage hill!

Do you. Think we will really get that much rain?
Yea I'm sure it will be like 2" per Hour at times and maybe 4" per hour.... we could get as much as 12" between tomorrow and Wed morning....

Taco :o)
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This storm is definately interesting to try to forcast.
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Quoting msgambler:
Wait, wife is cooking eggs, bacon , and grits. I may have to eat here first.....LOL



Cereal for my family..lol
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From the heavy rainfall reported seems the twin blob to the east is the rainmaker? Am I wrong? And if so, what is that blobs projected path. It is an outer feeder band right? So will it wrap around and go over Panama city/do than Alabama area ya think?
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Quoting JLPR2:


Weaker in this run. Still, it's too far out to celebrate. :P

I think Kirk (or whatever name this storm gets) will be a big one... You never see so many models on board for development this early on.

Member Since: February 11, 2012 Posts: 88 Comments: 8290
Here's a picture of my street flooding from earlier before the heaviest rain fell.
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I don't think Isaac will go through RI.

So get that out of your heads.
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Quoting txag91met:


It will be a hurricane by 8PM or 11PM.

or 2 am or 5 am or 8 am or 11 am or 2 pm or 5 pm.
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Quoting MiamiHurricanes09:
I'm going with a conservative 80kt maximum intensity at landfall.
I agree with this, 90 mph maybe up to 100 max? Looks like Isaac has been fighting dry air for several days or that is what I am hearing?
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What is the traffic like getting out of NOLA right now?
Is there any panic to leave town? I live in Houston, should I prepare for lots of out of town visitors to Htown?
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Quoting StormHype:


And it was forecast to be a Cat1 in Key West. It's still a TS and it's 250 miles NW of there now. It could happen, but how many times can they continue to be wrong on the intensity forecast? Not enough it seems. Cat2 is a cover-your-a** forecast based on the sensitivity of NOLA's issues. Just my opinion. Rainfall is going to be significant concern for sure.


Your comments reflect an attitude of many on this blog I find curious. Do you really think that the NHC could have done a better scientific job of predicting intensity and/or track, but for some incomprehensible reason, just refused to do so? Do you think they are just making mistakes with the data and that no one is checking the work? Do you think you could just fly in some other experts who know more about the science to do a better job? These people are likely the best there is, and anyone else would still have the same so-called "political" problems they do. They will be wrong (and right) until the science improves. Persuade the powers-that-be to spend the money to improve the research to improve knowledge base, then you will get better forecasts. (end of on-topic rant)
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Quoting GetReal:


It's more likely already there... IMO


There isn't any indication from recon that we are there yet. I would agree we are close to a hurricane, but we are not there yet.
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Rut ro, looking like a stall
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Man there is a lot of activity from mobile tonight. I am here off of cottage hill!

Do you. Think we will really get that much rain?
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Quoting hurrtracker1994:
Hello everyone just thought I would check in. Isaac is starting to develop a large CDO however wind shear continues to disrupt the CDO on the southwestern area of the storm. Also the dry air that Isaac was contending with earlier is finally starting to mix its way out. If the anticyclone can center itself over Isaac then we can start to see the storm intensify quicker. I would expect the storm to be a hurricane by the morning, if dry air and wind shear continue to lessen.



You can see the wind shear that is really making this system rather lopsided.


It will be a hurricane by 8PM or 11PM.
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330. JLPR2
Quoting MAweatherboy1:
Here comes Kirk...



Weaker in this run. Still, it's too far out to celebrate. :P
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Isaac looks a lot like Katrina when she left florida....he's just rotated 90 degrees.
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Quoting MiamiHurricanes09:
I'm going with a conservative 80kt maximum intensity at landfall.

I'm going with a strong cat1 to at the most moderate cat2. Then again Isaac could do the unexpected and RI, hopefully not and I don't think he will do that.
Member Since: March 16, 2012 Posts: 127 Comments: 7981
Quoting Masquer08er:
Same here. I just had disc surgery in my neck and my wife doesn't need a big clean up job LOL. Say something next time you see me.


I sure will say something. I hope your neck feels better. Just don't do anything to jar it trying to clean up!
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Wait, wife is cooking eggs, bacon , and grits. I may have to eat here first.....LOL
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Quoting Reb74:

Any thoughts to where it may go? GOM? East Coast?
To far out in time, but two things have happened that the people at the NHC and the models should be praised for..# 1- The mets saw that in the long range models a zonal flow pattern was practically a certainty. # 2- The models were on the money predicting the zonal flow way in advance..The bad news is that now with the zonal pattern nearly in place, and nothing in the northern hemisphere indicating a switch back to a high amplification pattern ( except maybe Isaac himself ) the storms that come off Africa will most likely reach our part of the world. Excluding waves that exit Africa north of the Cape Verde Islands. This sais it well..EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
331 PM EDT MON AUG 27 2012

VALID 12Z THU AUG 30 2012 - 12Z MON SEP 03 2012


...HEAVY RAINFALL EXPECTED WITH TROPICAL CYCLONE ISAAC AND ITS
REMNANTS...

STAYED CLOSE TO THE 00Z AND 12Z ECMWF FOR THE FRONTS AND PRESSURES
FOR DAYS 3 AND 4...SWITCHING TO A BLEND OF THE 00Z/12Z ECMWF AND
00Z EC ENSEMBLE MEAN THEREAFTER. THIS WAS DRIVEN LARGELY BY THE
ECMWF BEING CLOSEST TO THE OFFICIAL TRACK FOR ISAAC...BUT THE
ECMWF DOES MEET OUR EXPECTATIONS FOR THE NORTHERN STREAM FLOW TO
BECOME DECIDEDLY PROGRESSIVE...AS WE CURRENTLY OBSERVE NO BLOCKS
AROUND THE HEMISPHERE. GIVEN THE SEASON...THIS PROGRESSION WILL
LIKELY CARRY WAVES OF LOW TO MODERATE AMPLITUDE.
UNFORTUNATELY...SUCH A REGIME LEADS TO DECREASING CONFIDENCE AS
MODELS BECOME OUT OF PHASE BY DAYS 5/6. GIVEN THIS...AND THE
INFLUENCE OF ISAAC...THERE IS PERHAPS LESS THAN AVERAGE CONFIDENCE
IN THIS MEDIUM RANGE PERIOD.
IT IS NOTEWORTHY...THOUGH...THAT EVEN THE MODELS AND ENSEMBLE
MEMBERS THAT TRACK ISAAC FARTHER WEST DEPICT RECURVATURE AND
EASTWARD ACCELERATION BY DAY 6.

IN THE SHORT RANGE...A BRIEF AMPLIFICATION OF THE NORTHERN STREAM
FLOW WILL CAUSE AN EASTERN U.S. TROUGH TO BRUSH ACROSS
ISAAC...LIKELY STRETCHING THE SYSTEM AND ITS MOISTURE
EAST-NORTHEAST OF THE CENTER. A SURFACE HIGH ASSOCIATED WITH THE
AMPLIFICATION WILL BRING DRIER LOW LEVEL AIR INTO THE OHIO VALLEY
AND MID MISSISSIPPI VALLEY PRIOR TO ISAAC MOVING NORTH OF THE GULF
COAST STATES. THIS SUGGESTS THE HEAVY RAIN THREAT WILL REMAIN
INTACT NEAR THE CENTER OF THE CYCLONE...AND NOT EXPAND TOO FAR
NORTHWARD...BUT WILL RATHER EXPAND EASTWARD ACROSS THE TENNESSEE
VALLEY/SOUTHEAST STATES THROUGH DAY 4.

THERE IS A CLEAR TREND TOWARD SEEING A SHORT WAVE RIDGE CENTER
MIGRATE ACROSS THE TOP OF THE TROPICAL CYCLONE...BRINGING A BRIEF
HEAT WAVE TO THE OHIO VALLEY/MID ATLANTIC/NORTHEAST DAYS 4-6. THIS
SAME AREA WOULD THEN SEE A CHANCE OF HEAVY RAIN AND INCREASED WIND
ON DAYS 6/7 IF THE FORECAST FOR THE REMNANTS OF ISAAC VERIFIES.

BURKE/FRACASSO
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Quoting jeebsa:
No problem. Hey great job on the blog Largo appreciate all the maps and images
thanks, i hope i helped people today, the warnings were coming out so fast i could not keep up lol
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I'm going with a conservative 80kt maximum intensity at landfall.
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Quoting KEEPEROFTHEGATE:
then there will be four
and then there were four.
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Quoting LargoFl:
ok ty..good thing no one got hurt
No problem. Hey great job on the blog Largo appreciate all the maps and images
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Quoting msgambler:
On my way to Sheri's
Me Too :o)

Taco :o)
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then there will be four
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Here comes Kirk...

Member Since: February 11, 2012 Posts: 88 Comments: 8290
Quoting KEEPEROFTHEGATE:
soaking rains first of the fall storms 5 more will come 1 will be the one
yeah try the GFS at around 366 hours..a third one hits the same area
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Quoting LargoFl:
..thats storm number 2..going to the same place as issac according to the GFS
the next of five
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Quoting mobilebayal:


Oh wow! I have seen you. That's great! I am really curious to see what this storm brings. I sure hope not much.
Same here. I just had disc surgery in my neck and my wife doesn't need a big clean up job LOL. Say something next time you see me.
Member Since: August 16, 2007 Posts: 0 Comments: 397
Quoting Tazmanian:





its forcast too be come a cat 2


And it was forecast to be a Cat1 in Key West. It's still a TS and it's 250 miles NW of there now. It could happen, but how many times can they continue to be wrong on the intensity forecast? Not enough it seems. Cat2 is a cover-your-a** forecast based on the sensitivity of NOLA's issues. Just my opinion. Rainfall is going to be significant concern for sure.
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Quoting mobilebayal:




So, are you cooking for all of the Mobile people on here? When should we come?
On my way to Sheri's
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Quoting jeebsa:
No injuries but its between 20 and 30 Mobile homes.
ok ty..good thing no one got hurt
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Based on the models and an average of everybody's opinions.....I'm predicting landfall at Port Fourchon with 110 mph sustained.
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Quoting Dsntslp:
Peoples backyards are being washed into the drainage canals here. The cars on the road out front won't slow down and it pushes the water toward the yards and out the back and into the canal.
simply amazing whats happening over there
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Quoting LargoFl:
there have been no reports of tornado touchdowns, according to Bay News 9 Chief Meteorologist Mike Clay. However, a tornado has been reported in Indian River County, near Vero Beach, and damaged 20 mobiles home. There is no word as to injuries.
Local weather is expected to be rainy at times, with gusty winds for the rest of the day and night, Clay said. Thunderstorms could also develop quickly and produce torrential rainfall for the next few days.

In the last 72 hours, wind gusts as high as 49 mph were reported in the Bay area.
No injuries but its between 20 and 30 Mobile homes.
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NE quad is way too weak to get past Cat 1... 85mph peak IMO.

Member Since: February 11, 2012 Posts: 88 Comments: 8290
Quoting LargoFl:
..keeper if it does follow that path, the huge rains could indeed help those midwest drought states alot huh
soaking rains first of the fall storms 5 more will come 1 will be the one
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Quoting Masquer08er:
There was a jubilee last week too, right?


I think so. We have a house outside of Weeks Bay and so far have not had one this year. Last year, we had 4 in a row. Each one was different. It was really neat.
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Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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