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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Are you saying Euro West and GFS East?
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Recon showing west, Euro back to the west......
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Quoting wxchaser97:
Oh just saw the 2am advisory, I doubt Isaac makes it past 75-80mph now.

I am predicting a peak of 75 mph...tops....

And because of this....unless you think Gordon went cat 3 briefly...we have had zero...zip...notta..big goose egg # of major hurricanes in the Atlantic this season so far....amazing given the # of the storms. Goes to show that # isn't everything. I think we have a record low ACE (Accumlated Cyclone Energy) divided by # of storms...
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Quoting atmosweather:


That's gonna get this place all riled up later in the morning.


Is that landfall somewhere just east of Lake Charles then continuing into SE Texas!! *Shakes Head*
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Quoting MississippiWx:
Lol. Quite comical to see the Euro shift this much this late in the game.
I guess it is time for an upgrade.
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Quoting Bobbyweather:

That's false info. Leslie was at that intensity while extratropical.
Hurricane Gert of 1999 holds the record, I think. I might look for stronger storms, but I haven't got much time.
Hurricane Gert (1999)
70 mph 110 kph 964 mb Tropical Storm
Ok thanks for clearing that up. I think I got confused with one person posted the track from wunderground and another from wikipedia that had conflicting pressures.
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Oh just saw the 2am advisory, I doubt Isaac makes it past 75-80mph now. Surge and rain flooding were going to be Isaac's biggest threats anyway.
Member Since: March 16, 2012 Posts: 127 Comments: 7942
Quoting MississippiWx:
Lol. Quite comical to see the Euro shift this much this late in the game.


That's gonna get this place all riled up later in the morning.
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Quoting MississippiWx:
Lol. Quite comical to see the Euro shift this much this late in the game.


I agree its almost like the Euro and GFS keep swapping sides very late in the game...Mississippi...who do we believe!! LOL
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check out the current out flow of the storm and new convection around the center...

Link
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Quoting xtremeweathertracker:
Euro going west with Isaac!!

I don't want to discredit Euro too much...but I am going to post grahpic evidence on my blog that the GFS spot-on predicted the evolution of the blocking ridge developing to Isaac's north...while the Euro has been off.... so I don't know if I believe it now....(unless it has joined GFS)
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Lol. Quite comical to see the Euro shift this much this late in the game.
Member Since: July 15, 2006 Posts: 17 Comments: 10244
Quoting sar2401:


They can't find any non-contaminated winds of 75 mph or greater....just like the last 3,144 recon flights. :) The NHC, to its credit, is just reporting the actual facts, and not trying to CYA by reporting a hurricane when none exists.


Thank you very much for clearing that up for me. I will tell you this winds have picked up to about 25 mph here. They say tomorrow all heck breaks loose.
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2241. sar2401
Quoting atmosweather:


With each pass the flight level wind data comes back a little higher, despite these ridiculous internal processes failing to establish a proper eyewall, they are going to find a hurricane force surface wind real soon. Probably with the next major fire-up of eyewall convection.


Yep, real soon now...probably....could be...maybe not...for sure...I doubt it. Take your pick, any answer seems to be equally likely now. :)
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This storm is a bust in the GOM.

RIP to those souls lost in Haiti and elsewhere in the islands - no disrespect to them...

But I am afraid that there has been too many "chicken little" overblown media attention, due to Tampa / Republican convention...or TWC infiltration of NBC producers, or what...

But this just 'feels' more hyped than normal.

Surprised that NHC hasn't called it a hurricane just to get it to that status, but I respect the fact that they have kept it to TS even though I imagine they have had some pressure to upgrade it asap to hurricane.

Strange, strange storm indeed.

BTW, I get a kick: Adam Berg looking at a webcam on Bourbon Street "pretty calm right now, people evacuating, heeding our warnings" blah blah blah.

As if... its almost 1:15 a.m. on a Monday night. Has nothing to do with warnings. Kinda like the video of I-10 traffic "Both Ways!!" during rush hour. LOL.

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Glad the storm will remain week.Still gonna be severe flooding.Will the rain help the drought states?
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2238. sar2401
Quoting nolacane2009:
Been a long time lurker and come her for ever hurricane season but do not always post. I am in Terrytown, La which is south of NOLA. I was expecting it to be upgraded. (not that is what I want nor wishing on) What is keeping the NHC from upgrading Isaac?


They can't find any non-contaminated winds of 75 mph or greater....just like the last 3,144 recon flights. :) The NHC, to its credit, is just reporting the actual facts, and not trying to CYA by reporting a hurricane when none exists.
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2237. KEEPEROFTHEGATE (Mod)
Quoting sar2401:


Arf! I've been thinking a cat 1 by 5am for five days now...this is like rooting for the Cleveland Indians. :)
or the toronto maple leafs
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Quoting MississippiWx:
Highest reading.

Flt. Lvl. Wind (30s): From 77° at 74 knots (From the ENE at ~ 85.1 mph)
Air Temp: 16.0°C* (~ 60.8°F*)
Dew Pt: 16.0°C* (~ 60.8°F*)
Peak (10s) Flt. Lvl. Wind: 76 knots (~ 87.4 mph)
SFMR Peak (10s) Sfc. Wind: 57 knots (~ 65.5 mph)


With each pass the flight level wind data comes back a little higher, despite these ridiculous internal processes failing to establish a proper eyewall, they are going to find a hurricane force surface wind real soon. Probably with the next major fire-up of eyewall convection.
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Yawn. I'm SO sick of Isaac. why does he insist on keeping me up tonight....ugh
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Euro 48 hrs. has come west now. Really disappointed with the flip flopping back and forth with the models, but maybe I should cut them some slack, Isaac is a very fickle storm and is doing whatever he likes.

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2233. drj27
Weather Alert: reporting live from ft.walton beach the winds are blowing about 5mph I think it's time to start boarding up the windows also I would like my 2hours back that I lost from work today stay tuned for the next update as I'm sure the conditions will get worse when the winds get to 10 mph
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Quoting GTcooliebai:
Someone posted Leslie of 2000 had a pressure of 973 mb. and it was a 70 mph. TS.

That's false info. Leslie was at that intensity while extratropical.
Hurricane Gert of 1999 holds the record, I think. I might look for stronger storms, but I haven't got much time.
Hurricane Gert (1999)
70 mph 110 kph 964 mb Tropical Storm
Member Since: September 7, 2006 Posts: 89 Comments: 2655
2231. sar2401
Quoting WXGulfBreeze:


Gawd, is it 1AM CDT already?

Funny how time slips away with a few JD's and wind watching outside.

Nite!


GN, Gulf. I suspect nothing will have changed much when you get back here again at this rate.
Member Since: Posts: Comments:
Been a long time lurker and come her for ever hurricane season but do not always post. I am in Terrytown, La which is south of NOLA. I was expecting it to be upgraded. (not that is what I want nor wishing on) What is keeping the NHC from upgrading Isaac?
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Highest reading.

Flt. Lvl. Wind (30s): From 77° at 74 knots (From the ENE at ~ 85.1 mph)
Air Temp: 16.0°C* (~ 60.8°F*)
Dew Pt: 16.0°C* (~ 60.8°F*)
Peak (10s) Flt. Lvl. Wind: 76 knots (~ 87.4 mph)
SFMR Peak (10s) Sfc. Wind: 57 knots (~ 65.5 mph)
Member Since: July 15, 2006 Posts: 17 Comments: 10244
2228. sar2401
Quoting GTcooliebai:
Pressure down 1 more millibar. I'm thinking a hurricane at 5AM, but with this storm anything is possible.


Arf! I've been thinking a cat 1 by 5am for five days now...this is like rooting for the Cleveland Indians. :)
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Euro going west with Isaac!!
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Quoting sar2401:


Glad to hear that. I think we all need some sleep. I'm sure not staying up all night watching Miss Piggy again. :)


Gawd, is it 1AM CDT already?

Funny how time slips away with a few JD's and wind watching outside.

Nite!
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looks like any moment the winds are gonna just pop up
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Quoting NCHurricane2009:
1 AM CDT...

978 mb...70 mph tropical storm still...amazingly low central pressure for a tropical storm. Is this a record anyone know?

I am typing up my in-depth theory on my blog on why this has happened to Isaac....
Someone posted Leslie of 2000 had a pressure of 973 mb. and it was a 70 mph. TS.
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Quoting atmosweather:
Lmao they agree with MH09 and want to see our disappointed faces...remains 70 mph at 2AM.
I don't think they upgraded it because Pasch wrote the advisory and he doesn't want his original forecast to be wrong. ;)
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2222. cjnew
Quoting playapics:
Hey gang, long time lurker here. Would it be reasonable to suggest that Isaac may actually weaken given that his slow forward motion is causing cool water to well up starving him from fuel?

You are a long time lurker. Congrats on your first comment. :D

From what I know, Isaac would have to stay over the same area for much longer before upwelling becomes an issue. Say a day or so. The dry air has kept him in check and could end up weakening him.
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2221. KEEPEROFTHEGATE (Mod)
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Quoting washingaway:


Yeah, I know, but these wobbles can add up.


And it has, look at how many wobbles it's taken on its way up here.

Though, there is something rather uncomfortable about the last 8 fixes dragging to the west-north-west and now the west...

We shall see...
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2219. sar2401
Quoting atmosweather:
Lmao they agree with MH09 and want to see our disappointed faces...remains 70 mph at 2AM.

Fer cryin' out loud...they are never going to get this right. Maybe he'll become a cat 1 over TX....or somewhere.
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Quoting CaicosRetiredSailor:
Tropical Storm ISAAC
...ISAAC CONTINUES TO HEAD FOR THE NORTHERN GULF COAST...SIGNIFICANT STORM SURGE AND FRESHWATER FLOOD THREAT EXPECTED... ...U.S. Warnings in Effect...
1:00 AM CDT Tue Aug 28
Location: 27.4°N 87.7°W
Moving: NW at 12 mph
Min pressure: 978 mb
Max sustained: 70 mph


pressure still going down... DARN WINDS GO UP!!!!
Member Since: April 23, 2011 Posts: 104 Comments: 14873
Quoting nigel20:
...ISAAC CONTINUES TO HEAD FOR THE NORTHERN GULF COAST...SIGNIFICANT STORM SURGE AND FRESHWATER FLOOD THREAT EXPECTED...
1:00 AM CDT Tue Aug 28
Location: 27.4°N 87.7°W
Moving: NW at 12 mph
Min pressure: 978 mb
Max sustained: 70 mph
Pressure down 1 more millibar. I'm thinking a hurricane at 5AM, but with this storm anything is possible.
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Every time Isaac attempts to form an eye wall, convection warms and the process has to start all over again. Appears that might be the case right now as well. Beginning to doubt if Isaac ever makes it past 75mph.
Member Since: July 15, 2006 Posts: 17 Comments: 10244
2215. will40
000
WTNT34 KNHC 280559
TCPAT4

BULLETIN
TROPICAL STORM ISAAC INTERMEDIATE ADVISORY NUMBER 28A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
100 AM CDT TUE AUG 28 2012

...ISAAC CONTINUES TO HEAD FOR THE NORTHERN GULF COAST...SIGNIFICANT
STORM SURGE AND FRESHWATER FLOOD THREAT EXPECTED...


SUMMARY OF 100 AM CDT...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...27.4N 87.7W
ABOUT 145 MI...235 KM SE OF THE MOUTH OF THE MISSISSIPPI RIVER
ABOUT 220 MI...355 KM SSE OF BILOXI MISSISSIPPI
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...978 MB...28.88 INCHES
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Quoting sar2401:


Please, please, let this be a hurricane on the next update. This is like a blind date that never ends. :)

I take it you don't live in any of the affected areas?
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1 AM CDT...

978 mb...70 mph tropical storm still...amazingly low central pressure for a tropical storm. Is this a record anyone know?

I am typing up my in-depth theory on my blog on why this has happened to Isaac....
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2212. sar2401
Quoting KEEPEROFTHEGATE:
Taz has not been banned
his blog is still showing on page 3
of the members blog list
so he is just taking a break
maybe even sleeping


Glad to hear that. I think we all need some sleep. I'm sure not staying up all night watching Miss Piggy again. :)
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Tropical Storm ISAAC
...ISAAC CONTINUES TO HEAD FOR THE NORTHERN GULF COAST...SIGNIFICANT STORM SURGE AND FRESHWATER FLOOD THREAT EXPECTED... ...U.S. Warnings in Effect...
1:00 AM CDT Tue Aug 28
Location: 27.4°N 87.7°W
Moving: NW at 12 mph
Min pressure: 978 mb
Max sustained: 70 mph
Member Since: July 12, 2007 Posts: 0 Comments: 6032
Lmao they agree with MH09 and want to see our disappointed faces...remains 70 mph at 2AM.
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Not upgraded...
pressure lowered to978.
Member Since: September 7, 2006 Posts: 89 Comments: 2655
2208. nigel20
...ISAAC CONTINUES TO HEAD FOR THE NORTHERN GULF COAST...SIGNIFICANT STORM SURGE AND FRESHWATER FLOOD THREAT EXPECTED...
1:00 AM CDT Tue Aug 28
Location: 27.4°N 87.7°W
Moving: NW at 12 mph
Min pressure: 978 mb
Max sustained: 70 mph
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Euro 24 hrs.

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Quoting MiamiHurricanes09:
Hoping this doesn't get upgraded simply to see disappointment spread across the faces of WU users. ;)

I'm workin on a blog update after some analysis of Isaac again...to be released soon (for u late nighters)...

It will include the high-def detail on what's going on as usual...but basically I conclude he isn't gonna get stronger than 70 to 75 mph....
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Quoting will40:
wonder what the 2 update will say

My NHC webpage will not refresh...does anyone know if Isaac is still at 70 mph for 2 AM EDT (1AM CDT)?
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Hoping this doesn't get upgraded simply to see disappointment spread across the faces of WU users. ;)
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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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