Katrina wind speeds

John Farley

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I am wondering what information may now be available concerning measured wind speeds in Katrina, especially around the time of the final landfall near the LA/MS border. In a chase report on the Katrina thread, Chris Collura reported 150 mph sustained, 180 gusts between Gulfport and Biloxi. This was stronger than the NHC estimate at this time; if you are reading this, Chris, was this speed measured or your estimate? Also, does anyone know of other measured speeds that may have become recently available.

Satellite and radar loops of this landfall indicate two things:

1. There was a surge of lightning around the eastern part of the eyewall just before and during landfall.

2. There was a northeastward surge of intense precipitation from the eyewall at landfall, that passed right over Gulfport.

I am wondering if these may have indicated the hurricane was trying to go into a cycle of intensification right around the time of the final landfall; if so this might explain stronger than estimated winds in the Gulfport area. Just wondering if anyone has info that can shed light on this.
 
I find myself wondering if Katrina was a Cat 5 at landfall, considering the pressure was lower at landfall than Andrew was at landfall, and Andrew was revised as a Cat 5 a couple years ago. Correct me if Im wrong about hte pressure being lower than Andrew's. That, along with the fact there was a Cat 5 storm surge in MS.
 
Take a look at the raw data from the wind towers set up by the The Florida Coastal Monitoring Program at http://users.ce.ufl.edu/~fcmp/. They're max winds are not anywhere near 150 mph sustained. They did have gusts on their 10 m tower up to perhaps 120-140 mph. Even considering their somewhat inland location, I don't think anywhere saw category 4 sustained winds on the MS coastline. The wind damage just inland from the damaging surge doesn't compare to the kind of winds that hurcn "Andrew" inflicted in south FL. I'm judging this by the relative lack of severe and widespread roof damage between Andrew and Katrina in the aerial photos supplied by NOAA, the USGS and contacts with others down there such as Tim Marshall (see http://ngs.woc.noaa.gov/katrina/KATRINA0000.HTM). If anybody has some pictures from Andrew damage, it'd be great to pull them out of the archives and share them. This is not to diminish the experience that chasers had in the area because 120mph wind gusts are truely more horrific than most anybody can imagine.

Regarding the surge in convection at landfall, I liken that to enhanced shoreline convergence owing to differential friction as the eastern eyewall flow encountered land. The stronger convergence there could easily boost convection. Maybe that would yield some downdrafts and locally intense wind gusts but there is still nothing like what Andrew did. Katrina was still in decaying stage as the southwest eyewall was evaporating even more.


I am wondering what information may now be available concerning measured wind speeds in Katrina, especially around the time of the final landfall near the LA/MS border.

Satellite and radar loops of this landfall indicate two things:

1. There was a surge of lightning around the eastern part of the eyewall just before and during landfall.

2. There was a northeastward surge of intense precipitation from the eyewall at landfall, that passed right over Gulfport.

I am wondering if these may have indicated the hurricane was trying to go into a cycle of intensification right around the time of the final landfall; if so this might explain stronger than estimated winds in the Gulfport area. Just wondering if anyone has info that can shed light on this.
 
With due respect to the Florida Coastal Monitoring program, it does not appear their towers were in position to capture the highest wind speeds on the coast.

I noted the eyewall structure when the storm was southeast of New Orleans was considerably better than at landfall near Burras. Did it intensify? Maybe...there was plenty of water surrounding the storm at that point.

I don't know whether it was Cat 4 or 5 at this point, but I do not believe that decision can be based on the mobile towers.[/i]
 
I find myself wondering if Katrina was a Cat 5 at landfall, considering the pressure was lower at landfall than Andrew was at landfall, and Andrew was revised as a Cat 5 a couple years ago. Correct me if Im wrong about hte pressure being lower than Andrew's. That, along with the fact there was a Cat 5 storm surge in MS.
You have to remember though, that Katrina was much larger in size than Andrew. Thus the pressure gradient (and resulting wind field) would be weaker. Also, the surge lags changes in the wind speed...I've heard 24 hours thrown about as the period for that lag...


BC
 
My suspicion is that Katrina - from wind speed - will be rated a category 3 at landfall. But she was a category 3 with a category 5 storm surge. That storm surge, of course, is what did all the deadly and extensive damage with slates wiped clean, floating of casinos, damming of debris and deforestation on the coast.

It is also worth noting that Katrina was NOT the strongest hurricane EVER in the Gulf of Mexico at 902MB. Hurricane Allen in 1980 maxed out at 899MB.

KR
 
Hurricane Allen dropped to 899 millibars when it was in the Yucatan Channel, it did reach cat 5 status in the Gulf of Mexico but "only" 909 mb. Gilbert reached 888 mb in the Caribbean. I believe Katrina would be the strongest in history so far north in latitude?
 
I did just notice a Post-Tropical Cyclone Report from the Slidell NWS (like all of their products, issued through Mobile NWS) indicating that equipment near the center of Lake Pontchartrain measured sustained winds of 78 knots (about 90 mph) with gusts to 99 knots (about 115 mph). Most of the measurements elsewhere that are listed on this PNS were well before the final landfall. Note that winds on Lake Pontchartrain would have been on the west side of the eye, which would have likely been weaker than those on the east side of the eye around Gulfport.
 
I'm not surprised at the lack of wind observations showing that Katrina was any stronger than category 3 with the Mississippi coast landfall. In fact - the NHC 10 am advisory on the day of landfall concurred:

AT 10 AM CDT...1500Z...THE CENTER OF HURRICANE KATRINA WAS LOCATED NEAR LATITUDE 30.2 NORTH... LONGITUDE 89.6 WEST. THIS POSITION IS NEAR THE MOUTH OF THE PEARL RIVER...ABOUT 35 MILES EAST-NORTHEAST OF NEW ORLEANS LOUISIANA AND ABOUT 45 MILES WEST-SOUTHWEST OF BILOXI MISSISSIPPI........MAXIMUM SUSTAINED WINDS ARE NEAR 125 MPH...WITH HIGHER GUSTS. KATRINA IS NOW A CATEGORY THREE HURRICANE ON THE SAFFIR-SIMPSON SCALE.....THE MINIMUM CENTRAL PRESSURE ESTIMATED FROM AIR FORCE HURRICANE HUNTER AIRCRAFT IS 927 MB...27.37 INCHES.

So, the 'conflicting' evidence is the extreme storm surge (twice what would typically be expected for a storm of this strength) - values typically only associated with a category 5 hurricane. The MCP of 927 mb is more often associated with a category 4 hurricane, but as noted above there were some issues associated with eyewall disorganization as well as the storm being som incredibly large in size that would have limited the local pressure gradient. AOML already has the wind analyses available - and I'd note the wind distribution at landfall:

col02deg.png


Certainly, winds are highly assymetrically distributed, but only 110 knot (125 mph) winds were expected in the right eyewall, and that's for marine exposure. Also, the area with this peak wind is notably very small. I would have to assume that Chris was guessing the winds from experience - not measured, unless there were some local wind tunnel effects at his observing location.

Clearly, there is a lot about storm surge that was not well understood with this storm - perhaps more of a total kinetic energy of near surface winds summed up for the entire hurricane should be used for 'water moving potential' than the current first order guess of hurricane intensity alone.

Glen
 
Wasn't really concentrating on the micro-details at MI landfall. But I recall pretty clearly that the loops showed smaller multiple vorticies circulating just inside of the large main eyewall. This wouldn't be at all surprising, I think, and could explain the variance in the observations. Both the Cat 3 and Cat 4-5 folks may be correct, depending on their particular perspective.
 
With a lack of operating weather monitoring equipment at landfall you are going to have look at other sources to judge wind speed.

I've seen photos from Plaquemines Parish showing total defoliation. Does anybody know what kind of wind speeds are needed to do that? Defoliation probably isn't evidence of peak gusts, but long periods of high sustained winds.
 
I think Katrina should be studied for revamping the storm surge estimates given for specific category storms. I remember several cat 3's and 4's that produced no serious storm surge. I think Katrina was a natural wave/surge maker because of its slow forward speed and direction. I guess the geology of the landmass off the coast also plays a part. Any thoughts?

Mike
 
I remember several cat 3's and 4's that produced no serious storm surge.

Coastline shape and the bathymtry of the ocean floor plays a major role in storm surge magnitudes. Just look at what Isabel did with the Chesapeake Bay.
 
Defoliation occurs with Cat-2 winds pretty easily. Frances defoliated everything from Cocoa Beach on south.

I think the AOML estimated winds seem pretty reasonable though maybe slightly underestimated in some sections on the west side. Note that Slidell ASOS had a 137 mph peak gust.

regards,

Jim


Originally posted by B Ozanne
With a lack of operating weather monitoring equipment at landfall you are going to have look at other sources to judge wind speed.

I've seen photos from Plaquemines Parish showing total defoliation. Does anybody know what kind of wind speeds are needed to do that? Defoliation probably isn't evidence of peak gusts, but long periods of high sustained winds.
 
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