Hurricane Katrina, page 3
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reply posted on 25-8-2005 @ 02:51 PM by worldwatcher
Tropical Storm Katrina has just made it into a Hurricane...minimal, but a hurricane non the less

Hurricane KATRINA Update

000
WTNT62 KNHC 251940
TCUAT2
HURRICANE KATRINA TROPICAL CYCLONE UPDATE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
335 PM EDT THU AUG 25 2005

...RECONNAISSANCE AIRCRAFT REPORTS AND DOPPLER RADAR DATA INDICATES
THAT TROPICAL STORM KATRINA HAS STRENGTHENED INTO A HURRICANE...

SHORTLY BEFORE 330 PM EDT...REPORTS FROM A NOAA RECONNAISSANCE
AIRCRAFT AND NOAA DOPPLER RADAR DATA FROM MIAMI INDICATE MAXIMUM
SUSTAINED SURFACE WINDS INCREASED TO A CATEGORY ONE HURRICANE.

DATA FROM THE STEPPED-FREQUENCY MICROWAVE RADIOMETER ONBOARD THE
NOAA AIRCRAFT MEASURED HURRICANE-FORCE SURFACE WINDS...WHICH IS
SUPPORTED BY NOAA DOPPLER RADAR VELOCITY DATA FROM WFO MIAMI.

FORECASTER STEWART


sorry I'm not video capable quite yet

[edit on 8-25-2005 by worldwatcher]


reply posted on 25-8-2005 @ 05:34 PM by Indy
Unfortunately but expected you cannot find a single surface observation anywhere close to what the NHC reports as maximum sustained winds.

This observation station is closest to the center of the storm. It recorded a low central pressure of 29.06 but no wind over 45mph

www.wunderground.com...

Here is a list of observation stations near Boca Raton...

www.wunderground.com...

Higest reported wind speeds at 5pm central time was 37mph

Highest from Hollywood, FL was 39mph. Here is their link...

www.wunderground.com...

This observation which is monitored by the NDBC shows something a little better which is still only 42kts or about 46 or 47mph

www.ndbc.noaa.gov...

Here is another link to the NDBC dedicated to the hurricane. Highest observation from any of the points is 52kts or about 57mph.

www.ndbc.noaa.gov...

Thats about normal for the NHC. They overstate some 15 to 20mph. I challenge anyone to find an observation where the sustained wind (not gusts) is 65mph let alone 75mph.



reply posted on 25-8-2005 @ 06:20 PM by Indy
Here is an image of a storm that the NHC likes to call a hurricane. As of the latest update they have increased the winds to 80mph even though there hasn't been a 60mph sustained wind anywhere.



This storm in reality is poorly organized. The deep convention is mostly to the east and south of the center. There looks to be alot of dry air mixing in with the storm. There is no eye visible on this image either. Reason? This isn't a hurricane but a tropical storm that they are calling a hurricane. I know you'll think there is an eye based on radar but alot of tropical storms show this signature provided the center isn't fully exposed to dry air. Maximum sustained winds should be listed at 60mph. Maybe 65mph if you were lucky. That would be more consistent with the satellite signature and more consistent with the surface observations.


reply posted on 25-8-2005 @ 06:30 PM by Indy
Here is the wind and pressure history from Hollywood, FL which is on the north side of the center. The reports were collected here...

link
7:11pm 29.29" 54.1mph sustained Wind Easterly
7:02pm 29.25" 46.0mph sustained Wind Easterly
6:53pm 29.23" 43.7mph sustained Wind Easterly

6:45pm 29.20" 36.8mph sustained Wind ENE
6:38pm 29.21" 39.1mph sustained Wind NE
6:28pm 29.21" 40.3mph sustained Wind NE
5:53pm 29.21" 50.6mph sustained Wind NNE

After this point the wind is Northerly and the pressure is rising. This point is pre landfall. There are a couple reports where the wind was 52.9mph but thats as high as the sustained winds ever reach.



(mod edit to reduce large url to shorter link)

[edit on 26-8-2005 by pantha]


reply posted on 26-8-2005 @ 04:23 AM by Indy
The NHC fudging continues. Here is a statement from the 5am discusstion.

www.nhc.noaa.gov...

"WHILE THE LATEST DOPPLER RADAR VELOCITIES ONLY SUPPORT 60 KT AT THE SURFACE... THESE VALUES ARE STEADILY CLIMBING... AND THE FIRST DVORAK ESTIMATES OVER THE GULF ARE A UNANIMOUS T4.0/65 KT. THEREFORE... KATRINA IS REASSIGNED HURRICANE STATUS WITH INTENSITY OF 65 KT."

They are taking the higher estimate from a storm model over a real time dopler reading. Nice. Here is a more detailed description of Dvorak.

"The Dvorak technique is a method using enhanced Infrared and/or visible satellite imagery to quantitatively estimate the intensity of a tropical system. Cloud patterns in satellite imagery normally show an indication of cyclogenesis before the storm reaches tropical storm intensity. Indications of continued development and/or weakening can also be found in the cloud features. Using these features, the pattern formed by the clouds of a tropical cyclone, expected systematic development, and a series of rules, an intensity analysis and forecast can be made. This information is then standardized into an intensity code."

Source: www.ssd.noaa.gov...

So basically they think it looks like a 65 even though a real reading says its only 60. And even that 60 may be high depending on how much the NHC decides to trim off the higher altitude readings. Remember the dopler readings happen above the surface. You then take off a percentage to come up with the surface estimate. Its the same technique used by the hunters. This is where the problem comes in. Pre Andrew the percentage was higher. Post Andrew the percentage was lower. Before Andrew a 100kt wind observed by the hunters would equate to something like 75 or 80kts at the surface. Post Andrew they report it at around 90kts.

The only TRUE measure you have is a surface observation. Surface observations aren't subject to flight level to surface level adjustments. They are real time. And they don't support what the NHC says. Haven't in quite some time.
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