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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Good Morning...Isaac looks like a Hurricane now. You folks along the Northern Gulf Coast be safe.

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Not seeing anything that brings this system near Texas? I see southeast La then north thru Ark and then northeast? TODAY MODELS ARE IN BETTER CONSENSUS ON MOVEMENT OF ISAAC. THE
STORM WILL MOVE ON SHORE IN SOUTHEASTERN LA AND MOVE UP INTO AR.
THIS WILL MEAN MINIMAL IMPACTS HERE. WE WILL SEE WINDS GUSTING TO
THE 20S IN THE EASTERN COUNTIES WED AS ISAAC MOVES TOWARD THE
NORTH. OTHERWISE...THE STORM WILL HAVE NO EFFECT ON OUR WEATHER.

THU THE UPPER RIDGE WILL BUILD OVER THE SOUTHERN PLAINS. THIS WILL
END ANY CHANCE FOR PRECIP AND CAUSE TEMPS TO CLIMB. HOT AND DRY
WEATHER WILL CONTINUE THROUGH THE END OF THE FORECAST PERIOD.

FIRE WEATHER...
AS ISAAC MOVES THROUGH LA...THE PRESSURE GRADIENT WILL TIGHTEN
ACROSS EASTERN TX AND INTO OUR EASTERN COUNTIES. WINDS WILL
INCREASE TO 10 TO 15 MPH WITH GUSTS IN THE 20S. THURSDAY AND
FRIDAY AS THE TEMPS CLIMB...THE RH WILL DROP. THE MINIMUM RH WILL
DROP BELOW 30 PERCENT OVER MUCH OF THE WESTERN HALF OF OUR CWA THU
AND FRI AFTERNOONS. BY SAT RETURN FLOW FROM THE GULF WILL ALLOW RH
TO RECOVER.
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Quoting RTSplayer:


Taz is a little over-aggressive.

95 to 100 peak intensity at the surface, but that won't be in 3 hours unless something insane happens.

more like 9 to 12 hours from now...


I agree,the overall size of storm has become smaller and the central pressure has been dropping,that should mean an increasing wind speed.
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Quoting Fl30258713:


Right. He actually had NOAA create Isaac using a special tropical storm voodoo dance he learned in Kenya, so he could make this speech to reassure people in NOLA who went through Katrina, that if needed FEMA would be on scene with emergency supplies ASAP.

Quite the conspiracy.

Now back to reality and Isaac.

Thank you for your time.


Wow! Never said he created the storm lol. Was making a joke, just un-wad yer drawers and lighten up. I went through Katrina as well as many others. Ah well I'm done with it. C-ya.
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All eyes are on Isaac which is vital to people along the Golf Coast - but - again today there is an area just off FLA/GA/SC that seems to be an outflow from Isaac that looks really nasty. I don't recall this happening during other storms - this is what caused all of the serious storms on the east coast of FLA yesterday and there is a piece that wants to start inland around the NC/SC border.
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101 mph flightlevel?
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Did anyone note what the position of that high wind dropsonde was - way away from the center - probably in a thunderstorm.
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Dry air is the best friend that LA has right now.
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Quoting 9030mike:

This is what I think as well. Dry spot that got wrapped up looks like an eye.


Sure. It's a dry spot, that just happens to be surrounded by hurricane strength wind maximi, to show a sharp temperature gradient, and to have the pressure of a Category 2 storm.

Whatever you're smoking, I wish you'd share some. Must be good stuff.
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Quoting 9030mike:

This is what I think as well. Dry spot that got wrapped up looks like an eye.


no the southern part was dry air however now, its a true eye.
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Quoting weatherh98:
who is john oldshoe?


WU I-Witness???
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Quoting GetReal:


NHC may have to increase intensity at landfall back to a Cat 2....


Starting to look much more organized.
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Quoting weatherh98:


we are ready.

we have hot dogs sausage steak beer ice and a generator for the neighbrs:)



Man, that sounds like some pretty good grub. I'm in Houston but I'll be right over. lol
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John Oldshue (WU) has the best reports on TWC. No I'm not biased. He is REALLY GOOD. And, no we're not related.
Member Since: August 16, 2007 Posts: 0 Comments: 397
3039. WxLogic
Now that for a second time it has a fairly good eye... will it keep it!!!. I personally believe it will collapse once more before trying again for may be a last time.

I say this because there's too much dry air for Isaac to sustain an eye for too long... especially being this close to the coast:



At low levels... it has been doing a good job at shielding the entrainment of low PW into its core. If it's able to keep this up then it might have chance at keeping a 75MPH to 80MPH strength until landfall... but it has to watch itself at mid to upper levels for dry air. As shown below too:

12Z LIX:

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Quoting pipelines:


The dry spot is not an eye, sorry

Its an eye.
Member Since: March 16, 2012 Posts: 127 Comments: 7940
who is john oldshoe?
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I live 20 miles west of NOLA. Starting to see gust to about 35 mph. Skies cloudy with light rain. Prepared to ride it out with a week worth of supplies.
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WU on TWC...live interview.
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I know this sounds kinda mean and nasty of me to say, but I really hope this makes landfall in SE Louisiana near New Orleans. The reason being is that if Isaac decided to move westward at a slow pace over increasingly warm waters towards the upper Texas coast, it would give him a significantly longer time to strengthen to a monster hurricane and this would create a nightmare scenario for those people further west caught off guard.
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Quoting pipelines:


The dry spot is not an eye, sorry



Per recon data, satellite, and NHC position it is and same with the most recent microwave pass. Some you guys seem in shock and denial that after all of Isaacs struggles it might have finally reached hurricane status.
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Quoting pipelines:


The dry spot is not an eye, sorry

This is what I think as well. Dry spot that got wrapped up looks like an eye.
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Quoting Masquer08er:
Thinking this is dry air with the COC SE of that point. What do you think?


No, an eye
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3029. GetReal


NHC may have to increase intensity at landfall back to a Cat 2....
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3028. Patrap
New Orleans
NEXRAD Radar

Base Reflectivity 0.50° Elevation
Range 248 NMI

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Quoting RitaEvac:
The last frame tells it all with the eye showing now
Thinking this is dry air with the COC SE of that point. What do you think?
Member Since: August 16, 2007 Posts: 0 Comments: 397
3026. AUradar
Whats the deal with the WonderMap? It has its last track point as due north of the previous track point????
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Quoting Tazmanian:
i think we see winds up too 90 too 100mph winds at 10am
I don't think so. FL winds only support about a 85mph system. It could strengthen to 100mph, though.
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Quoting WxNerdVA:


Isaac is wrapping convection around the northern part of the eye now.


The dry spot is not an eye, sorry
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Quoting StormHype:


At the surface? LMAO at you.


Taz is a little over-aggressive.

95 to 100 peak intensity at the surface, but that won't be in 3 hours unless something insane happens.

more like 9 to 12 hours from now...
Member Since: January 25, 2012 Posts: 33 Comments: 1520
I'm sure for most posters here, the debate over strong Cat 1 vs weak Cat 2 is really irrelevent. The important factors insofar as New Orleans is concerned are:

1. Huge, slow moving, extremely wet system
2. Massive storm surge up to 15 ft.
3. Rainfall up to another 2 ft.

Katrina devasted New Orleans - which it missed - due to rain and surge, not winds. The "repairs" have been criticized and remain of concern. They will be severely tested in the next couple of days.

Frankly, it's my fear and concern that another failure is very possible, yet evacuations have been ordered only outside the city. This is foolhardy. Pray for NO.
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The last frame tells it all with the eye showing now
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Shortwave has a defined eye, though maybe still a tiny bit of openness to the west.

RGB shows a defined eye with slight upper level cloud occlusion.


The outflow is still screwed up with this storm, as it continues to have a upper level cyclone embedded in the anti-cyclone, as it did even before passing Cuba. It's just complete a-typical configuration. Maybe it's half-way between true tropical and sub-tropical characteristics in the upper levels, even though the low and mid levels are obviously becoming more and more hurricane-like.


I continue to expect at least a borderline cat1/cat2 landfall, as the models insiste it will be intensifying at landfall and even several hours thereafter.

Remember, this is Louisiana, much of what is "Land" on map is actually rivers and marshes, not even counting the labelled rivers and lakes, so intensification after landfall is not unreasonable, it has happened before in the Yucatan and Florida as well.


Look for 95 to 100mph sustained while it is stalled or nearly stalled over NOLA or just west of them.
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Viking!

Morning, we are up just a bit, maybe a foot but nothing like the 6' in PCB. I will keep an eye on it, since there are 30+/- boats anchored out that normally are not here... All is quite here, grey skies with a light breeze.
Quoting 69Viking:


Up maybe a foot just West of Fort Walton Beach on the Sound. Noticed Isaac went more North than West at the last avisory and has really slowed down, could he be turning North sooner than they forecast or is this a jog? Guess we'll see at the next advisory if this trend continues!














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Quoting TXCWC:


lol...thanks...I have worked all night and HAVE to get sleep anyway...so you can be sure I have said all I will on this...GFS AND EURO say what they say...NOT ME SAYING IT. :)


Lol. That was my problem too. Sleep works wonders. :)
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Hopefully the strengthening trend doesn't continue or NOLA will have even more problems.
Member Since: March 16, 2012 Posts: 127 Comments: 7940
Quoting Tazmanian:
i think we see winds up too 90 too 100mph winds at 10am


At the surface? LMAO at you.
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Agree with the earlier comment that NHC is/needs to issue a special advisory upgrading the status to hurricane within the next hour if not sooner.
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Quoting floridaboy14:
looks like he finally got an eye. based on his speed it looks like he will get shoved due west possibly into texas


Can't wait to see if you are right or wrong on this... Yep you are wrong
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Quoting FelixTheKat:


im see dry air enter from the NW
I think the dry air is getting closed off.
Member Since: August 16, 2007 Posts: 0 Comments: 397
Quoting hydrus:
This is the most organized I have seen this system become so far. Those folks in LA know what to do, I hope there ready.


we are ready.

we have hot dogs sausage steak beer ice and a generator for the neighbrs:)
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i think we see winds up too 90 too 100mph winds at 10am
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Quoting Gumbogator:
Landfall according to the NHC track is Grand Isle La with the idea that Isaac will bend to the West. New Orleans Metro could take a long duration hit. This will be a water storm/event. The drought in Arky and points north should be helped.


Not to mention constant onshore winds blowing into Lake Pontchartrain.
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Quoting HimacaneBrees:
Well Obama will be speaking at 10 EDT about Isaac. Campaign tactic? Think I'd rather watch QVC.


Right. He actually had NOAA create Isaac using a special tropical storm voodoo dance he learned in Kenya, so he could make this speech to reassure people in NOLA who went through Katrina, that if needed FEMA would be on scene with emergency supplies ASAP.

Quite the conspiracy.

Now back to reality and Isaac.

Thank you for your time.
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Things gonna get dicey for NOLA as long as these trends continue, if it gets to 100mph then NOLA, you're gonna have some problems at the angle it's coming into you at.
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The GFS, Euro and Nam all show SE Texas recieving 45 to 50 Knot 850 MB winds in 36 to 48 Hrs!





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Quoting WxNerdVA:


Isaac is wrapping convection around the northern part of the eye now.

If he sustains it then Isaac could do a little more strengthening.
Member Since: March 16, 2012 Posts: 127 Comments: 7940
looks like he finally got an eye. based on his speed it looks like he will get shoved due west possibly into texas
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Quoting Masquer08er:
I'll step in it and say C, but some will want F) none of the above
I always hated that in school, marking the wrong letter. B -80MPH, But I'll stand by my mistake
Member Since: August 16, 2007 Posts: 0 Comments: 397

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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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