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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Isaac has a lot of winds on its south side most likely...
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Quoting GetReal:


Apparently you are not familiar with the area of GOM Isaac is currently located.... That water is very deep (Mississippi Canyon) and warm.


Maybe he meant "shallow" close to shore - as TWC talked about in regards to impact of storm surge.
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Isaac
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 28 AUG 2012 Time : 124500 UTC
Lat : 28:00:15 N Lon : 88:43:10 W


CI# /Pressure/ Vmax
3.6 / 987.1mb/ 57.0kt


Final T# Adj T# Raw T#
3.6 4.0 4.8

Estimated radius of max. wind based on IR : 17 km

Center Temp : -18.6C Cloud Region Temp : -55.8C

Scene Type : EYE

Positioning Method : RING/SPIRAL COMBINATION

Ocean Basin : ATLANTIC
Dvorak CI > MSLP Conversion Used : ATLANTIC

Tno/CI Rules : Constraint Limits : 0.5T/hour
Weakening Flag : OFF
Rapid Dissipation Flag : OFF

C/K/Z MSLP Estimate Inputs :
- Average 34 knot radii : 160km
- Environmental MSLP : 1014mb

Satellite Viewing Angle : 36.0 degrees

************************************************* ***
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Quoting reedzone:


Your right, that is a large dry slot and the eye is right under it... Storms with very low pressure have small (pinhole) intense eyes.. This is going to be worse then what people think for New Orleans.


Radar shows that he is really cranking up. I don't think there is any question in my mind that he still achieve at least a 90 knot storm. Maybe a even a bit more. People should have been prepared though NHC has done a pretty darn good job with this system for 4-5 days outlooks.
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3100. Pastey
Baton Rouge checking in. I appreciate everyone continuing to post between updates. I've been following this storm for about a week now. I'm expecting weak Cat1 or strong TS winds here in Baton Rouge early tomorrow morning and into the mid-day. We're obviously still sunny here with a light breeze and some moderate cloud cover. I'll continue to post updates as the day and evening progresses. Thanks again for everyone's insight and updates.
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Quoting RickWPB:
Lake Okeechobee is up to 13.12' today. One good thing from all the rain in the past two days.

Now they just need to empty lake O a week before the next tropical system threatens, like they did a few years ago.
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Dr. Knabb winds just below hurricane force.
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Quoting GetReal:



Time for today's underwater geography lesson....




Isaac is most likely BARELY off the continental shelf...

Has anyone heard anything on the louisiana sinkhole?
Will Isaac make it bigger?
Will all that water get in there and lessen the explosion threat?
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Quoting Patrap:
Uptown, the first feeder has arrived, Very layered Atmo noted thru as we can see the CDO to the Se.

IM-PREssive

Good to see you blogging, even on vacation, Patrap! Stay safe (and have a Fresca)
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80MPH Hurricane at 11AM. Latest Dropsonde.

Significant Temperature And Relative Humidity Levels...
Level Air Temperature Dew Point
988mb (Surface) 25.8C (78.4F) 25.3C (77.5F)
850mb 19.8C (67.6F) 18.4C (65.1F)
764mb 17.0C (62.6F) 16.0C (60.8F)
752mb 14.8C (58.6F) 14.8C (58.6F)

Significant Wind Levels...
Level Wind Direction Wind Speed
988mb (Surface) 195 (from the SSW) 70 knots (81 mph)
983mb 190 (from the S) 67 knots (77 mph)
970mb 185 (from the S) 77 knots (89 mph)
939mb 190 (from the S) 81 knots (93 mph)
909mb 195 (from the SSW) 74 knots (85 mph)
896mb 200 (from the SSW) 67 knots (77 mph)
850mb 210 (from the SSW) 64 knots (74 mph)
752mb 220 (from the SW) 54 knots (62 mph)
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President to speak on Isaac at 10:00 a.m. EST.
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Quoting MAweatherboy1:
It looks like there are two eye like features in Isaac now. I think the larger one farther north is a dry spot, and then the smaller, more obscured one a little further south is the eye.

No, the northern spot is the eye, and southern spot is a small dry area that is already filling in.



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Quoting atmosweather:


Probably not all the way closed still...latest RECON fix from 30 minutes ago showed it being open SE to SW. He could still close it off and begin to organize faster, although he has tried this process countless times over the last 48 hours only to have the eyewall eroded away by dry air entrainment and being slightly displaced from its mid level spin.

L. Eye Character: Open from the southeast to the southwest
M. Eye Shape & Diameter: Circular with a diameter of 30 nautical miles (35 statute miles)


Thanks for your helpful response!
(Folks, the response was made early this morning; not current.)
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3090. Patrap
Uptown, the first feeder has arrived, Very layered Atmo noted as we can see the CDO to the Se.

IM-PREssive
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Quoting SrChiefFan1:


At least this POTUS has someone in charge of FEMA that knows something about disaster response instead of horse grooming....
If you want to rant about politics, go to MSNBC.
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Quoting weatherh98:


no he is.

Yah I know, took him a pretty long time to do so.
Member Since: March 16, 2012 Posts: 127 Comments: 7927
Recon looks to be heading for the center, 976.7mb so far, but they're not there yet.
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3086. RickWPB
Lake Okeechobee is up to 13.12' today. One good thing from all the rain in the past two days.
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Im sorry, but this has to be a Hurricane.
Member Since: August 1, 2007 Posts: 0 Comments: 167
3084. Patrap
New Orleans
NEXRAD Radar

Base Reflectivity 0.50° Elevation
Range 248 NMI



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sat shows eye still just covered slightly
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3080. jcxt
Nice page of near real time wind speeds, pressure and water levels of Gulf coast stations.


http://tidesandcurrents.noaa.gov/quicklook/data/I SAAC.html
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3079. GetReal
Quoting TomballTXPride:
Looking like a very low end category 1 for landfall...probably 80mph. Shallow continental shelf waters and much dry air still disrupting the center now now will keep intensity in check. Still big surge though.



Time for today's underwater geography lesson....


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3078. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting MAweatherboy1:
It looks like there are two eye like features in Isaac now. I think the larger one farther north is a dry spot, and then the smaller, more obscured one a little further south is the eye.



Your right, that is a large dry slot and the eye is right under it... Storms with very low pressure have small (pinhole) intense eyes.. This is going to be worse then what people think for New Orleans.
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Quoting TomballTXPride:

It appears both are dry air pockets according to Mid-level dry air analysis. See post 3039.

No, one of them is an eye, it has been reported by recon.
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Quoting wxchaser97:

Yup and with the dropsonde saying 80mph surface I think Isaac is a hurricane.


no he is.
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It's looking to me like Isaac has made hurricane status.

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Quoting CybrTeddy:



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.

Not questioning that it's a hurricane, because it is. I'm questioning two frames of sat because just a couple hours ago, everyone was claiming a different dry spot was an eye, which is now gone I may add.
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Quoting CybrTeddy:



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.
Not at all. Just don't think the dry spot is the "eye". There is an eye developing, though.
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Quoting wxchaser97:

Yup and with the dropsonde saying 80mph surface I think Isaac is a hurricane,


When/where was that dropsonde?
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Just a reminder, this strengthening isnt totally unexpected, Isaac was forecasted to be a 90-100mph storm at landfall, and the NHC factored that into their shear forecast....so this extra strengthening isnt going to make this storm anymore catastropic than it was forecast to be from the beginning, and certain isnt going to make it flood NOLA if it want forecasted to do so before.
Unless it bombs out immensely between now and landfall, which is unlikely now that it is up on the continental shelf, the classic hurricane weakening zone...it wont be catastropic
The strengthening and finally wrapping around is more likely due to land friction pileup than anything isaac did differently than before, but it is almost out of time.
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The weather channel just said recon found 101 mph flight level wind and could be a hurricane in the next advisory
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Quoting TheThinker:
Pre. Obama on TV to talk about Isaac? Will turn it off too. Know what he will say, It's Bush's fault! LOL!


At least this POTUS has someone in charge of FEMA that knows something about disaster response instead of horse grooming....
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They say big rain in S FL today:/
Member Since: May 23, 2012 Posts: 0 Comments: 4392
twc says no upgrade till next advisory.... 1.5 hours from now


also 101 flight level winds
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Just when I'm on the edge of my seat for recon to show data from the NE quadrant, both planes have stopped reporting data—or at least it isn't showing up in Google Earth. Anyone else having this problem?
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3061. GetReal
Quoting TomballTXPride:
Looking like a very low end category 1 for landfall...probably 80mph. Shallow continental shelf waters and much dry air still disrupting the center now now will keep intensity in check. Still big surge though.


Apparently you are not familiar with the area of GOM Isaac is currently located.... That water is very deep (Mississippi Canyon) and warm.
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Quoting weatherh98:
101 mph flightlevel?

Yup and with the dropsonde saying 80mph surface I think Isaac is a hurricane.
Member Since: March 16, 2012 Posts: 127 Comments: 7927
Check out the WV loop near the end...AWESOME...convective wrap around the eye...

Link
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It looks like there are two eye like features in Isaac now. I think the larger one farther north is a dry spot, and then the smaller, more obscured one a little further south is the eye.

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Quoting aasmith26:


WU I-Witness???


Ya but whats his handle?
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Quoting pipelines:


The dry spot is not an eye, sorry


Yes, it is.

It shows up as an eye on 3 different radar stations, and has been discussed by TWC meteorologists and Dr. Knabb at NHC, unless you think the director of NHC doesn't know wtf an "eye" is...
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Good Morning...Isaac looks like a Hurricane now. You folks along the Northern Gulf Coast be safe.

Member Since: August 31, 2009 Posts: 0 Comments: 5628

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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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