9/15/04 NOW: Hurricane Ivan [Gulf Coast]

[Morgan Palmer]

I'm not a technical radar expert, and I've never seen this addressed in anything I've read. Despite the narrow pulse width of 88D, I imagine there is significant absorption of the energy by the time the beam goes (lets say) directly through the eyewall.

How much might a current representation of the opposite eyewall be diminished?

Thanks for the help (good to know now and in the future).

mp

 

[B Ozanne]

Originally posted by Morgan Palmer
I'm not a technical radar expert, and I've never seen this addressed in anything I've read. Despite the narrow pulse width of 88D, I imagine there is significant absorption of the energy by the time the beam goes (lets say) directly through the eyewall.

How much might a current representation of the opposite eyewall be diminished?

Thanks for the help (good to know now and in the future).

mp

I've thought about that, but it doesn't really happen. Case in point is all the other hurricanes I've watched on radar, the beam made it through them just fine. Also the dry spot is in the same spot on multiple radars.

 

[David Schuttler]

Local News live video

http://video.wpmi.com/viewer/viewerpage.ph...hp?Art_ID=36468

 

[AlDanks]

Check out the base velocity radar from Mobile. It looks like Ivan has pegged the system on winds to and from the radar site.

If you go to the site and view the radar loop it looks like the eye will either go right straight up Mobile bay, or maybe slide just to the East - less storm surge in the bay.


http://www.seekthetruthfirst.com/ivan-mobile.jpg

http://weather.cod.edu/analysis/paulradar.pl?MOB

 

[mikegeukes]

Local TV Stations to follow the action:

Biloxi MS-Gulfport MS
http://www.wlox.com/ WLOX (Ch. 13) ABC
http://www.fox25.com/ WXXV (Ch. 25) FOX

Mobile AL-Pensacola FL:
http://www.weartv.com/ WEAR (Ch. 3) ABC
http://www.wkrg.com/ WKRG (Ch. 5) CBS
http://www.wpmi.com/ WPMI (Ch. 15) NBC

New Orleans LA:
http://www.wwltv.com/ WWL (Ch. 4) CBS
http://www.theneworleanschannel.com/index.html WDSU (Ch. 6) NBC
http://www.fox8live.com/ WVUE (Ch. 8 FOX
http://abc26.trb.com/ WGNO (Ch. 26) ABC

Panama City FL:
http://www.wjhg.com/ WJHG (Ch. 7) NBC
http://www.wmbb.com/ WMBB (Ch. 13) ABC

Local Newspapers: to follow the action:
http://www.sunherald.com/mld/sunherald/ -Biloxi MS
http://www.al.com/mobileregister/ -Mobile AL
http://www.nola.com/ -New Orleans LA
http://www.newsherald.com/index.shtml -Panama CIty FL
http://www.pensacolanewsjournal.com/ -Pensacola FL
http://www.picayuneitem.com/ -Picayune MS

Mike

 

[Mike Smith]

Morgan,
Actually, a WSR-88D radar, which is a 10cm "S" band radar can suffer from signal attenuation (also known as "rain fade") due to heavy rain. At the 10cm wavelength attenuation does not become significant until heavy rain or hail is occurring near or over the radar site -- which has become the case has Ivan has moved closer to the Mobile radar antenna. So, it is possible part of the back side of the eye is not being shown because the signal is being attenuated.

If you would like to email me off line ([email protected]), I would be happy to forward a couple of the graphics we use in WeatherData's internal radar training to illustrate this point.
Mike

 

[Tim Vasquez]

Which official (federal) site is reporting the strongest winds so far? As far as I can tell it is Pensacola NAS (KNPA) with 66 kt (76 mph) gusts, however it's hard to tell if other sites aren't getting plotted on my maps.

 

[B Ozanne]

Originally posted by Mike Smith
Morgan,
Actually, a WSR-88D radar, which is a 10cm \"S\" band radar can suffer from signal attenuation (also known as \"rain fade\") due to heavy rain. At the 10cm wavelength attenuation does not become significant until heavy rain or hail is occurring near or over the radar site -- which has become the case has Ivan has moved closer to the Mobile radar antenna. So, it is possible part of the back side of the eye is not being shown because the signal is being attenuated.

If you would like to email me off line ([email protected]), I would be happy to forward a couple of the graphics we use in WeatherData's internal radar training to illustrate this point.
Mike

Yes, it is possible. But in this case that is not what is happening as multiple radars are showing the same clear spot.

 

[Jeff Snyder]

I don't think the lack of precip in the western part of the eyewall has much to do with attenuation (loss of energy along the path) simply because it radar is picking up strong echoes in the eastern part of the eyewall. The amount and magnitude from the radar site the western part and the radar site to the eastern part looks pretty much the same, so any attenuation would pretty much be the same... If this was a case of the southern part having signficantlly weaker returns than ther northern eyewall, I could see a case for attenuation, as signal absorption from the precip in the northern eyewall could be signficant. However, this isn't the case so...

The central pressure continues to come up rapidly, as the eyewall falls apart.

 

[mikegeukes]

DPIA1 - Dauphin Island, AL
1005 PM CDT
Wind Direction (WDIR): ENE ( 60 deg true )
Wind Speed (WSPD): 61 kts
Wind Gust (GST): 77 kts
Atmospheric Pressure (PRES): 28.97 in

http://www.ndbc.noaa.gov/station_page.php?...p?station=dpia1
http://www.srh.noaa.gov/mob/marine.shtml

Mike

 

[mikegeukes]

Local Storm Report from the Tallahassee Office
1030 PM TORNADO 5 SE CYPRESS 30.67N 85.02W
09/15/2004 JACKSON FL AMATEUR RADIO
SPOTTED ON I-10 AND HIGHWAY 171 INTERSTECTION.

1040 PM TORNADO CYPRESS 30.72N 85.08W
09/15/2004 JACKSON FL EMERGENCY MNGR
*** 5 INJ *** TRAILER PARK HEAVILY DAMAGED. SOME
RESIDENTS STILL UNACCOUNTED FOR.
http://kamala.cod.edu/offs/KTLH/0409160349.nwus52.html

Mike

 

[Tim Vasquez]

Crap.. looks like we lost Pensacola obs. I think Gulf Breeze and Pensacola are going to get absolutely hammered.

Tim

 

[Jeff Snyder]

The intense convection that has persisted off and on for the past hour along the eastern eyewall is pretty interesting... The eyewall, on radar, has expanded, and there is almost no precipitation in the southern semicircle of this hurricane. Looking at the degradation of the structure per radar and now-eclipsed radar, I can't imagine the sustained 135mph winds will verify, but we'll see...

 

[mikegeukes]

2 AM EDT Observation: NAS Pensacola FL
KNPA 160556Z 12062G85KT 1/16SM +RA VV000 24/24 A2876 SLP740 P0024 60180 8//// T02390239 10244 20239 402610239 /PA 1130 DA 2500/

Wind from the ESE (120 degrees) at 71 MPH (62 KT) gusting to 98 MPH (85 KT) Preesure: 28.76 in. (973 mb)

Mike

 

[Jeff Snyder]

CNN has a correspondant in Gulf Shores, which is where the hurricane is landfalling. Interestingly, he says that he experienced considerably stronger winds in Frances than he's had so far in the northeastern eyewall. Now, he did say that there are a couple of buildings around him that may be influencing the winds. He says there is absolutely no way the winds are near 130mph, which is interesting since there is a strong tendency to exaggerate or over-estimate wind speed...

The eyewall, per MOB radar, has nearly collapsed. Precipitation is SLOWLY redeveloping over the southwestern quadrant of the storm, which has been precip-free (per radar) for many hours... I'd be surprised to see even high-end Cat 3 winds verify.

Last recon, at 1130pm central time, had 939mb central pressure with 122kt max flight-level winds (observed several hours earlier). Given the pressure rise of about 8mb in about as many hours, and the collapse of the eyewall (vortex message said the eyewall was "poorly defined"), I just don't think we're going to end up with the catastrophic Cat 4 that looked likely a couple of days ago...

EDIT: Ivan officially made landfall at Gulf Shores. I did find an interesting link with images of the storm surge potential impact for the Mobile / Gulf Shores area ... check out http://www.csc.noaa.gov/products/alabama/htm/hssra.htm ...