Katrina H-Wind Analysis, marginal 3 at landfall

[fasterdisaster]

OT: Wow this thread is quite popular!!

Katrina took out many trees here in Miami. It was the most vigorous Category 1(when it hit here) I had ever seen.

[Recurve]

Cat 3 winds and above cause real destruction. Houses will probably be ripped apart. Some NHC descriptions make anything but Cat 5 sound less destructive, but a lot of construction is not up to coastal standards. A roof without hurricane straps is a sail , walls without a roof collapse, windows without shutters break and let winds blow roof decking off, even with hurricane straps.

Many variables too. "Storm structure," where the winds are was mentioned. Duration -- one-and-a-half hours of Andrew's winds vs. more hours of lower winds from a slower/larger storm. Mesovortices in spiral bands (http://www.srh.noaa.gov/mlb/bonniemeso.html). Weakening of structures by gusts (when you want to tear something down, you pound on it, not push constantly).

The trajectory of the eye. If your structure survives a pass into the eye after gradually increasing winds, at the other edge of the eyewall, winds go from nearly calm to the highest sustained winds in a matter of seconds, from the opposite direction. Seemingly the exact mix of forces that will explode a weakened structure.

If you are in an area traversed by the width of the storm but miss the eye, you don't have the break in sustained winds from eye passage, you have wind direction changing throughout by as much as 180 degrees, acting on structures in more than one direction to tear them apart.

I think, no confirmation, that water-laden winds can have an effect on damage. If storm winds carry enough ocean spray or rain, with the same windspeed, seems the additional density of the wind would have a greater force. Or am I misstating the windspeed/density/force factor? If it takes more energy to move denser air at the same speed, I assume a hurricane can supply that.

[kevin]

As I've posted in another thread...

A 918 mb storm will do 918 mb damage.

However you debate it, I believe that the NHC will only move Katrina's winds at landfall up or down 5 mph. The bottom line is that Kat was a Cat 4 at landfall in LA and a strong Cat 3 at landfall in MS.

Huh?? A 918 mb storm will do 918 mb damage?

So a 1004 mb storm will have the same winds regardless of structure or surrounding pressures? Doesn't make sense, because we all know that at different mb's storms have been lower and weaker than others and so on.

???

I meant that a hurricane with a 918 mb pressure, regardless of its winds (trust me, they won't be of Cat 2 strength or lower), will do what you would expect a 918 mb hurricane (marginal Cat 5) would do, even if it is not a Cat 5. Likewise, a hurricane with 980 mb pressure you should expect strong Cat 1 damage regardless of wind speeds.

This is meant as a general rule of thumb. If a hurricane stalls and causes flash flooding the intensity does not matter. But otherwise it works well.

A 918 mb hurricane with 130 mph winds will do exactly 130 mph in damage. Pressure doesn't cause trees to uproot, shingles to fly off, debris to strike windows, or the vast majority of the storm surge. Wind and windfields are all that matter.

[fasterdisaster]

As I've posted in another thread...

A 918 mb storm will do 918 mb damage.

However you debate it, I believe that the NHC will only move Katrina's winds at landfall up or down 5 mph. The bottom line is that Kat was a Cat 4 at landfall in LA and a strong Cat 3 at landfall in MS.

Huh?? A 918 mb storm will do 918 mb damage?

So a 1004 mb storm will have the same winds regardless of structure or surrounding pressures? Doesn't make sense, because we all know that at different mb's storms have been lower and weaker than others and so on.

???

I meant that a hurricane with a 918 mb pressure, regardless of its winds (trust me, they won't be of Cat 2 strength or lower), will do what you would expect a 918 mb hurricane (marginal Cat 5) would do, even if it is not a Cat 5. Likewise, a hurricane with 980 mb pressure you should expect strong Cat 1 damage regardless of wind speeds.

This is meant as a general rule of thumb. If a hurricane stalls and causes flash flooding the intensity does not matter. But otherwise it works well.

No that makes no sense whatsoever. A 918 mb hurricane with 130 mph winds will do exactly 130 mph in damage. Pressure doesn't cause trees to uproot, shingles to fly off, debris to strike windows, or the vast majority of the storm surge. Wind and windfields are all that matter.

You do mean 140 mph in damage? RIGHT???

[kevin]

As I've posted in another thread...

A 918 mb storm will do 918 mb damage.

However you debate it, I believe that the NHC will only move Katrina's winds at landfall up or down 5 mph. The bottom line is that Kat was a Cat 4 at landfall in LA and a strong Cat 3 at landfall in MS.

Huh?? A 918 mb storm will do 918 mb damage?

So a 1004 mb storm will have the same winds regardless of structure or surrounding pressures? Doesn't make sense, because we all know that at different mb's storms have been lower and weaker than others and so on.

???

I meant that a hurricane with a 918 mb pressure, regardless of its winds (trust me, they won't be of Cat 2 strength or lower), will do what you would expect a 918 mb hurricane (marginal Cat 5) would do, even if it is not a Cat 5. Likewise, a hurricane with 980 mb pressure you should expect strong Cat 1 damage regardless of wind speeds.

This is meant as a general rule of thumb. If a hurricane stalls and causes flash flooding the intensity does not matter. But otherwise it works well.

No that makes no sense whatsoever. A 918 mb hurricane with 130 mph winds will do exactly 130 mph in damage. Pressure doesn't cause trees to uproot, shingles to fly off, debris to strike windows, or the vast majority of the storm surge. Wind and windfields are all that matter.

You do mean 140 mph in damage? RIGHT???

I was using a hypothetical....

And NO I do not mean 140mph in damage, I mean 130mph in damage. 130mph winds would cause 130mph damage, and 140mph winds would cause 140mph damage. My point was pressure doesn't matter only wind does.

[fasterdisaster]

Oh, sorry . I didn't realize you were using a hypothetical.

[timNms]

000
WTNT32 KNHC 291254
TCPAT2
BULLETIN
HURRICANE KATRINA INTERMEDIATE ADVISORY NUMBER 26B
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
8 AM CDT MON AUG 29 2005

...LARGE AND EXTREMELY DANGEROUS CATEGORY FOURHURRICANE KATRINA
POUNDING SOUTHEASTERN LOUISIANA AND SOUTHERN MISSISSIPPI...

A HURRICANE WARNING IS IN EFFECT FOR THE NORTH CENTRAL GULF COAST
FROM MORGAN CITY LOUISIANA EASTWARD TO THE ALABAMA/FLORIDA
BORDER...INCLUDING THE CITY OF NEW ORLEANS AND LAKE PONTCHARTRAIN.

A TROPICAL STORM WARNING AND A HURRICANE WATCH ARE IN EFFECT FROM
EAST OF THE ALABAMA/FLORIDA BORDER TO DESTIN FLORIDA...AND FROM
WEST OF MORGAN CITY TO INTRACOASTAL CITY LOUISIANA.

A TROPICAL STORM WARNING IS ALSO IN EFFECT FROM DESTIN FLORIDA
EASTWARD TO INDIAN PASS FLORIDA...AND FROM INTRACOASTAL CITY
LOUISIANA WESTWARD TO CAMERON LOUISIANA.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...INCLUDING POSSIBLE
INLAND WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED
BY YOUR LOCAL WEATHER OFFICE.

AT 8 AM CDT...1300Z...THE CENTER OF HURRICANE KATRINA WAS LOCATED
NEAR LATITUDE 29.7 NORTH... LONGITUDE 89.6 WEST OR ABOUT 40 MILES
SOUTHEAST OF NEW ORLEANS LOUISIANA AND ABOUT 65 MILES SOUTHWEST OF
BILOXI MISSISSIPPI.

KATRINA IS MOVING TOWARD THE NORTH NEAR 15 MPH...AND A GRADUAL TURN
TO THE NORTH-NORTHEAST AT A SLIGHTLY FASTER FORWARD SPEED IS
EXPECTED OVER THE NEXT 24 HOURS. ON THIS TRACK...THE CENTER WILL BE
PASSING JUST TO THE EAST OF NEW ORLEANS DURING THE NEXT FEW HOURS
WITH THE WORST OF THE WEATHER FOR THAT CITY OCCURRING OVER THE NEXT
COUPLE OF HOURS. THE CENTER IS EXPECTED TO MOVE INTO SOUTHERN
MISSISSIPPI LATER TODAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 135 MPH...WITH HIGHER GUSTS.
KATRINA IS AN EXTREMELY DANGEROUS CATEGORY FOUR HURRICANE ON THE
SAFFIR-SIMPSON SCALE. WEAKENING IS FORECAST AS THE CIRCULATION
INTERACTS WITH LAND TODAY. WINDS AFFECTING THE UPPER FLOORS OF
HIGH-RISE BUILDINGS WILL BE SIGNIFICANTLY STRONGER THAN THOSE NEAR
GROUND LEVEL.

KATRINA IS A VERY LARGE HURRICANE. HURRICANE FORCE WINDS EXTEND
OUTWARD UP TO 125 MILES FROM THE CENTER...AND TROPICAL STORM FORCE
WINDS EXTEND OUTWARD UP TO 230 MILES. PASCAGOULA MISSISSIPPI CIVIL
DEFENSE REPORTED A WIND GUST TO 118 MPH...AND GULFPORT MISSISSIPPI
EMERGENCY OPERATIONS CENTER REPORTED SUSTAINED WINDS OF 94 MPH WITH
A GUST TO 100 MPH.. BELLE CHASSE LOUISIANA...JUST SOUTHEAST OF NEW
ORLEANS...RECENTLY REPORTED SUSTAINED WINDS OF 76 MPH WITH A GUST
TO 88 MPH. A LITTLE EARLIER...BELLE CHASE REPORTED A GUST TO 105
MPH. NEW ORLEANS LAKEFRONT AIRPORT RECENTLY REPORTED SUSTAINED
WINDS OF 69 MPH WITH A GUST TO 86 MPH.

THE MINIMUM CENTRAL PRESSURE RECENTLY REPORTED BY AN AIR FORCE
RESERVE UNIT RECONNAISSANCE AIRCRAFT WAS 923 MB...27.26 INCHES.


000
WTNT32 KNHC 291438
TCPAT2
BULLETIN
HURRICANE KATRINA ADVISORY NUMBER 27
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
10 AM CDT MON AUG 29 2005

...CENTER OF POWERFUL HURRICANE KATRINA AGAIN MOVING ASHORE...NEAR
THE LOUISIANA-MISSISSIPPI BORDER...CONTINUES POUNDING SOUTHEASTERN
LOUISIANA AND SOUTHERN MISSISSIPPI...

A HURRICANE WARNING IS IN EFFECT FOR THE NORTH CENTRAL GULF COAST
FROM MORGAN CITY LOUISIANA EASTWARD TO THE ALABAMA/FLORIDA
BORDER...INCLUDING THE CITY OF NEW ORLEANS AND LAKE PONTCHARTRAIN.

AT 10 AM CDT...1500Z..ALL HURRICANE WATCHES ARE DISCONTINUED.
A TROPICAL STORM WARNING REMAINS IN EFFECT FROM EAST OF THE
ALABAMA/FLORIDA BORDER TO INDIAN PASS FLORIDA...AND FROM WEST OF
MORGAN CITY TO CAMERON LOUISIANA.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...INCLUDING POSSIBLE
INLAND WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED
BY YOUR LOCAL WEATHER OFFICE.

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.

KATRINA IS MOVING TOWARD THE NORTH NEAR 16 MPH...AND THIS GENERAL
MOTION IS EXPECTED TO CONTINUE TODAY AND TONIGHT. ON THIS TRACK
THE CENTER WILL MOVE OVER SOUTHERN MISSISSIPPI TODAY AND INTO
CENTRAL MISSISSIPPI THIS EVENING.

MAXIMUM SUSTAINED WINDS ARE NEAR 125 MPH...WITH HIGHER GUSTS.
KATRINA IS NOW A CATEGORY THREE HURRICANE ON THE SAFFIR-SIMPSON
SCALE. WINDS AFFECTING THE UPPER FLOORS OF HIGH RISE BUILDINGS
WILL BE SIGNIFICANTLY STRONGER THAN THOSE NEAR GROUND LEVEL.
WEAKENING IS FORECAST DURING THE NEXT 24 HOURS AS THE CENTER MOVES
OVER LAND. HOWEVER...HURRICANE FORCE WINDS ARE EXPECTED TO SPREAD
AS FAR AS 150 MILES INLAND ALONG THE PATH OF KATRINA. SEE INLAND
HURRICANE AND TROPICAL STORM WARNINGS FROM NATIONAL WEATHER SERVICE
FORECAST OFFICES.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 125 MILES FROM THE
CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP
TO 230 MILES.

THE MINIMUM CENTRAL PRESSURE ESTIMATED FROM AIR FORCE HURRICANE
HUNTER AIRCRAFT IS 927 MB...27.37 INCHES.

COASTAL STORM SURGE FLOODING OF 15 TO 20 FEET ABOVE NORMAL TIDE
LEVELS...ALONG WITH LARGE AND DANGEROUS BATTERING WAVES...CAN BE
EXPECTED NEAR AND TO THE EAST OF THE CENTER. STORM SURGE FLOODING
OF 10 TO 15 FEET...NEAR THE TOPS OF THE LEVEES...IS STILL POSSIBLE
IN THE GREATER NEW ORLEANS AREA. SIGNIFICANT STORM SURGE FLOODING
IS OCCURRING ELSEWHERE ALONG THE CENTRAL AND NORTHEASTERN GULF OF
MEXICO COAST.

RAINFALL TOTALS OF 5 TO 10 INCHES...WITH ISOLATED MAXIMUM AMOUNTS OF
15 INCHES...ARE POSSIBLE ALONG THE PATH OF KATRINA ACROSS THE GULF
COAST AND THE TENNESSEE VALLEY. RAINFALL TOTALS OF 4 TO 8 INCHES
ARE POSSIBLE ACROSS THE OHIO VALLEY INTO THE EASTERN GREAT LAKES
REGION TUESDAY AND WEDNESDAY.

A FEW TORNADOES ARE POSSIBLE OVER PORTIONS OF SOUTHERN AND EASTERN
MISSISSIPPI...SOUTHERN AND CENTRAL ALABAMA...AND THE WESTERN
FLORIDA PANHANDLE TODAY.

REPEATING THE 10 AM CDT POSITION...30.2 N... 89.6 W. MOVEMENT
TOWARD...NORTH NEAR 16 MPH. MAXIMUM SUSTAINED WINDS...125 MPH.
MINIMUM CENTRAL PRESSURE... 927 MB.

INTERMEDIATE ADVISORIES WILL BE ISSUED BY THE NATIONAL HURRICANE
CENTER AT NOON CDT AND 2 PM CDT FOLLOWED BY THE NEXT COMPLETE
ADVISORY AT 4 PM CDT.

FORECASTER PASCH


000
WTNT32 KNHC 291654
TCPAT2
BULLETIN
HURRICANE KATRINA INTERMEDIATE ADVISORY NUMBER 27A
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
NOON CDT MON AUG 29 2005

...KATRINA STILL POWERFUL BUT GRADUALLY WEAKENING AS IT MOVES
FARTHER INLAND...

A HURRICANE WARNING IS IN EFFECT FOR THE NORTH CENTRAL GULF COAST
FROM MORGAN CITY LOUISIANA EASTWARD TO THE ALABAMA/FLORIDA
BORDER...INCLUDING THE CITY OF NEW ORLEANS AND LAKE PONTCHARTRAIN.

A TROPICAL STORM WARNING REMAINS IN EFFECT FROM EAST OF THE
ALABAMA/FLORIDA BORDER TO INDIAN PASS FLORIDA...AND FROM WEST OF
MORGAN CITY TO CAMERON LOUISIANA.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...INCLUDING POSSIBLE
INLAND WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED
BY YOUR LOCAL WEATHER OFFICE.

AT NOON CDT...1700Z...THE CENTER OF HURRICANE KATRINA WAS LOCATED
NEAR LATITUDE 30.8 NORTH... LONGITUDE 89.6 WEST OR ABOUT 40 MILES
SOUTH-SOUTHWEST OF HATTIESBURG MISSISSIPPI.

KATRINA IS MOVING TOWARD THE NORTH NEAR 17 MPH...AND THIS GENERAL
MOTION IS EXPECTED TO CONTINUE TODAY AND TONIGHT. ON THIS TRACK
THE CENTER WILL CONTINUE MOVING OVER SOUTHERN MISSISSIPPI TODAY AND
INTO CENTRAL MISSISSIPPI THIS EVENING AND TONIGHT.

MAXIMUM SUSTAINED WINDS HAVE DECREASED TO NEAR 105 MPH...WITH HIGHER
GUSTS. KATRINA IS NOW A CATEGORY TWO HURRICANE ON THE
SAFFIR-SIMPSON SCALE. WINDS AFFECTING THE UPPER FLOORS OF HIGH
RISE BUILDINGS WILL BE SIGNIFICANTLY STRONGER THAN THOSE NEAR
GROUND LEVEL. WEAKENING IS FORECAST DURING THE NEXT 24 HOURS AS
THE CENTER MOVES OVER LAND. HOWEVER...HURRICANE FORCE WINDS ARE
EXPECTED TO SPREAD AS FAR AS 150 MILES INLAND ALONG THE PATH OF
KATRINA. SEE INLAND HURRICANE AND TROPICAL STORM WARNINGS FROM
NATIONAL WEATHER SERVICE FORECAST OFFICES.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 125 MILES FROM THE
CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP
TO 230 MILES. FAR FROM THE CENTER...DAUPHIN ISLAND ALABAMA REPORTED
SUSTAINED WINDS OF 76 MPH WITH A GUST TO 102 MPH...MOBILE ALABAMA
REPORTED A WIND GUST TO 83 MPH...AND PENSACOLA FLORIDA REPORTED
SUSTAINED WINDS OF 52 MPH WITH A GUST TO 69 MPH.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 940 MB...27.76 INCHES.

COASTAL STORM SURGE FLOODING ALONG THE NORTHERN AND NORTHEASTERN
GULF OF MEXICO COAST WILL BEGIN TO SLOWLY SUBSIDE LATER TODAY.

RAINFALL TOTALS OF 5 TO 10 INCHES...WITH ISOLATED MAXIMUM AMOUNTS OF
15 INCHES...ARE POSSIBLE ALONG THE PATH OF KATRINA ACROSS THE GULF
COAST AND THE TENNESSEE VALLEY. RAINFALL TOTALS OF 4 TO 8 INCHES
ARE POSSIBLE ACROSS THE OHIO VALLEY INTO THE EASTERN GREAT LAKES
REGION TUESDAY AND WEDNESDAY.

A FEW TORNADOES ARE POSSIBLE OVER PORTIONS OF SOUTHERN AND EASTERN
MISSISSIPPI...SOUTHERN AND CENTRAL ALABAMA...AND THE WESTERN
FLORIDA PANHANDLE TODAY.

REPEATING THE NOON CDT POSITION...30.8 N... 89.6 W. MOVEMENT
TOWARD...NORTH NEAR 17 MPH. MAXIMUM SUSTAINED WINDS...105 MPH.
MINIMUM CENTRAL PRESSURE... 940 MB.

AN INTERMEDIATE ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE
CENTER AT 2 PM CDT FOLLOWED BY THE NEXT COMPLETE ADVISORY AT 4 PM
CDT.

FORECASTER PASCH


000
WTNT32 KNHC 292051
TCPAT2
BULLETIN
HURRICANE KATRINA ADVISORY NUMBER 28
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
4 PM CDT MON AUG 29 2005

...KATRINA CONTINUES WEAKENING OVER MISSISSIPPI BUT STRONG WINDS AND
HEAVY RAINS STILL A THREAT...

AT 4 PM CDT...2100Z...THE HURRICANE WARNING FOR LAKE PONTCHARTRAIN
AND FROM THE MOUTH OF THE PEARL RIVER EASTWARD TO THE
ALABAMA/FLORIDA BORDER IS CHANGED TO A TROPICAL STORM WARNING. ALL
OTHER WARNINGS ARE DISCONTINUED.

A TROPICAL STORM WARNING REMAINS IN EFFECT FOR LAKE PONTCHARTRAIN
AND
FROM THE MOUTH OF THE PEARL RIVER EASTWARD TO THE ALABAMA/FLORIDA
BORDER. THIS WARNING WILL LIKELY BE DISCONTINUED THIS EVENING.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...INCLUDING POSSIBLE
INLAND WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED
BY YOUR LOCAL WEATHER OFFICE.

AT 4 PM CDT...2100Z...THE CENTER OF HURRICANE KATRINA WAS LOCATED
NEAR LATITUDE 31.9 NORTH... LONGITUDE 89.6 WEST OR ABOUT 30 MILES
NORTHWEST OF LAUREL MISSISSIPPI.

KATRINA IS MOVING TOWARD THE NORTH NEAR 18 MPH...AND A GRADUAL TURN
TO THE NORTH-NORTHEAST WITH AN ADDITIONAL INCREASE IN FORWARD SPEED
IS EXPECTED DURING THE NEXT 24 HOURS. ON THIS TRACK THE CENTER
WILL BE MOVING OVER CENTRAL AND NORTHERN MISSISSIPPI TONIGHT AND
INTO WESTERN TENNESSEE ON TUESDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 75 MPH...WITH HIGHER GUSTS.
KATRINA IS A CATEGORY ONE HURRICANE ON THE SAFFIR-SIMPSON SCALE.
CONTINUED WEAKENING IS FORECAST DURING THE NEXT 24 HOURS.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 60 MILES FROM THE
CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 205
MILES...MAINLY TO THE SOUTHEAST.

AT 2 PM CDT...A WIND GUST TO 110 MPH WAS MEASURED...BEFORE
INSTRUMENT FAILURE...IN LAUREL MISSISSIPPI BY JONES COUNTY
EMERGENCY MANAGEMENT.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 960 MB...28.35 INCHES.

COASTAL STORM SURGE FLOODING ALONG THE NORTHERN AND NORTHEASTERN
GULF OF MEXICO COAST WILL SLOWLY SUBSIDE.

STORM TOTAL RAINFALL TOTALS OF 4 TO 8 INCHES...WITH ISOLATED MAXIMUM
AMOUNTS OF 10 INCHES...WILL ACCOMPANY KATRINA FROM THE GULF COAST
THROUGH THE TENNESSEE AND OHIO VALLEYS.

A FEW TORNADOES ARE POSSIBLE OVER PORTIONS OF CENTRAL...EASTERN...
AND NORTHERN ALABAMA...AS WELL AS PORTIONS OF WESTERN GEORGIA AND
THE WESTERN FLORIDA PANHANDLE THIS EVENING.

REPEATING THE 4 PM CDT POSITION...31.9 N... 89.6 W. MOVEMENT
TOWARD...NORTH NEAR 18 MPH. MAXIMUM SUSTAINED WINDS... 75 MPH.
MINIMUM CENTRAL PRESSURE... 960 MB.

AN INTERMEDIATE ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE
CENTER AT 7 PM CDT FOLLOWED BY THE NEXT COMPLETE ADVISORY AT 10 PM
CDT.

FYI I'm 20 miles east of Laurel. It was a bit windy here

[wxmann_91]

As I've posted in another thread...

A 918 mb storm will do 918 mb damage.

However you debate it, I believe that the NHC will only move Katrina's winds at landfall up or down 5 mph. The bottom line is that Kat was a Cat 4 at landfall in LA and a strong Cat 3 at landfall in MS.

Huh?? A 918 mb storm will do 918 mb damage?

So a 1004 mb storm will have the same winds regardless of structure or surrounding pressures? Doesn't make sense, because we all know that at different mb's storms have been lower and weaker than others and so on.

???

I meant that a hurricane with a 918 mb pressure, regardless of its winds (trust me, they won't be of Cat 2 strength or lower), will do what you would expect a 918 mb hurricane (marginal Cat 5) would do, even if it is not a Cat 5. Likewise, a hurricane with 980 mb pressure you should expect strong Cat 1 damage regardless of wind speeds.

This is meant as a general rule of thumb. If a hurricane stalls and causes flash flooding the intensity does not matter. But otherwise it works well.

A 918 mb hurricane with 130 mph winds will do exactly 130 mph in damage. Pressure doesn't cause trees to uproot, shingles to fly off, debris to strike windows, or the vast majority of the storm surge. Wind and windfields are all that matter.

A 918 mb hurricane has the potential to do Cat 5 damage, even with 130 mph winds. The windfield could be small but it's all irrelavent because the area that gets the maximum damage could get Cat 5 damage. Somehow nature compensates. A weakening hurricane will retain low pressures, and the surge damage in one would be maximized. A strengthening hurricane will have relatively high pressures initially, so thus the wind damage would be the main factor. We all know wind is less damaging then surge. Sure pressure does not cause damage but what I'm saying is that the pressure can correlate with the damage.

I hope that clears it up. It's just a theory though. Whatever the case is IMHO winds are overrated.

[f5]

Katrina's storm surge looks like a CAT 5 went threw there entire TOWNS were flattened such as waveland,pass christian ect

[HurricaneBill]

Katrina's storm surge looks like a CAT 5 went threw there entire TOWNS were flattened such as waveland,pass christian ect

That's why I'd classify Katrina as a Category 5 based on storm surge and pressure.

I know, I know. It's determined by sustained wind and sustained wind only. But let's be honest here, there is a HECK of a lot more to a hurricane than sustained winds.

If the pressure and storm surge far exceed the level of sustained winds, I see nothing wrong with bending the SS scale rules a bit.

[tornadochaser86]

surface winds keyword surface what they are at the surface hurricane hunters measure winds at 3000 ft the winds dont always make it to the ground

[Frank P]

On my block on the front beach in Biloxi I don't think we lost an Oak Tree... my neighbors lost several large limbs, and their Oak by highway 90 has severe erosion, but all are still intact... I have two great Oaks in my front yard as does all my neigbors and they all survived, my large Magnolia, large pecan tree and several large Oaks in the back yard also did well... maybe they survived because they were all in 15 feet of water....

pine trees were another matter, they were down all over the place, some uprooted and some snapped about half way up...

[Derek Ortt]

918mb has absolutely no bearing on the damage. Not sure where that belief came from to be honest, as the laws of physics dictate otherwise

The NHC advisories typically are subject to revisions of as much as 20%; thus, they do not provide much value to the debate. The NHC advisory said Floyd hit Eleuthra with winds of 155m.p.h., but best track had it hitting with 120 m.p.h. winds

[timNms]

918mb has absolutely no bearing on the damage. Not sure where that belief came from to be honest, as the laws of physics dictate otherwise

The NHC advisories typically are subject to revisions of as much as 20%; thus, they do not provide much value to the debate. The NHC advisory said Floyd hit Eleuthra with winds of 155m.p.h., but best track had it hitting with 120 m.p.h. winds

So, Derek, if they NHC advisories are of no value, why do they bother to make them?

[Derek Ortt]

there of value operationally, but not in a scientific sense.

All real time data is subject to a significant quality control process before the finished product is available. NHC advisories are real time data

[wxmann_91]

918mb has absolutely no bearing on the damage. Not sure where that belief came from to be honest, as the laws of physics dictate otherwise

Well, I'm not sure whether to continue this debate, but I guess healthy debate is good for the forum... (not direct bashing, of course)

Maybe what I said was unclear. 918 mb is not what causes the damage. But usually a hurricane with pressure of 918 mb is a marginal Cat 5. So, regardless of wind, one can expect a hurricane with a pressure of 918 mb to do damage of marginal Cat 5, where the maximum damage is done. Of course, overall, damage will differ because of a hurricane's size, where it makes landfall, etc., but where the max damage is expect marginal Cat 5 damage.

I believe that we could create a scale where we could use the pressure as the main intensity indicator. Then, we could estimate just how damaging a hurricane will be. (So like if a hurricane has a pressure of 950 mb we could estimate that it will do strong Cat 3 damage.)

[Derek Ortt]

the SS scale used to be based upon pressure, until Dr Sheets became NHC director, when wind became the determinant.

Major problems as Gloria was a 942mb cat 3 at Hatteras, even though Hat sustained little damage from a 90KT cat 2 passing to the east, and Long Island did not receive cat 3 damage. We also had 90KT cat 4's. That method created more problems than it solved

[f5]

The Saffir-Simpson Hurricane Scale
--------------------------------------------------------------------------------

The Saffir-Simpson Hurricane Scale is a 1-5 rating based on the hurricane's present intensity. This is used to give an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall. Wind speed is the determining factor in the scale, as storm surge values are highly dependent on the slope of the continental shelf and the shape of the coastline, in the landfall region. Note that all winds are using the U.S. 1-minute average.

Category One Hurricane:
Winds 74-95 mph (64-82 kt or 119-153 km/hr). Storm surge generally 4-5 ft above normal. No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Some damage to poorly constructed signs. Also, some coastal road flooding and minor pier damage. Hurricane Lili of 2002 made landfall on the Louisiana coast as a Category One hurricane. Hurricane Gaston of 2004 was a Category One hurricane that made landfall along the central South Carolina coast.


Category Two Hurricane:
Winds 96-110 mph (83-95 kt or 154-177 km/hr). Storm surge generally 6-8 feet above normal. Some roofing material, door, and window damage of buildings. Considerable damage to shrubbery and trees with some trees blown down. Considerable damage to mobile homes, poorly constructed signs, and piers. Coastal and low-lying escape routes flood 2-4 hours before arrival of the hurricane center. Small craft in unprotected anchorages break moorings. Hurricane Frances of 2004 made landfall over the southern end of Hutchinson Island, Florida as a Category Two hurricane. Hurricane Isabel of 2003 made landfall near Drum Inlet on the Outer Banks of North Carolina as a Category 2 hurricane.


Category Three Hurricane:
Winds 111-130 mph (96-113 kt or 178-209 km/hr). Storm surge generally 9-12 ft above normal. Some structural damage to small residences and utility buildings with a minor amount of curtainwall failures. Damage to shrubbery and trees with foliage blown off trees and large trees blown down. Mobile homes and poorly constructed signs are destroyed. Low-lying escape routes are cut by rising water 3-5 hours before arrival of the center of the hurricane. Flooding near the coast destroys smaller structures with larger structures damaged by battering from floating debris. Terrain continuously lower than 5 ft above mean sea level may be flooded inland 8 miles (13 km) or more. Evacuation of low-lying residences with several blocks of the shoreline may be required. Hurricanes Jeanne and Ivan of 2004 were Category Three hurricanes when they made landfall in Florida and in Alabama, respectively.


Category Four Hurricane:
Winds 131-155 mph (114-135 kt or 210-249 km/hr). Storm surge generally 13-18 ft above normal. More extensive curtainwall failures with some complete roof structure failures on small residences. Shrubs, trees, and all signs are blown down. Complete destruction of mobile homes. Extensive damage to doors and windows. Low-lying escape routes may be cut by rising water 3-5 hours before arrival of the center of the hurricane. Major damage to lower floors of structures near the shore. Terrain lower than 10 ft above sea level may be flooded requiring massive evacuation of residential areas as far inland as 6 miles (10 km). Hurricane Charley of 2004 was a Category Four hurricane made landfall in Charlotte County, Florida with winds of 150 mph. Hurricane Dennis of 2005 struck the island of Cuba as a Category Four hurricane.


Category Five Hurricane:
Winds greater than 155 mph (135 kt or 249 km/hr). Storm surge generally greater than 18 ft above normal. Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. All shrubs, trees, and signs blown down. Complete destruction of mobile homes. Severe and extensive window and door damage. Low-lying escape routes are cut by rising water 3-5 hours before arrival of the center of the hurricane. Major damage to lower floors of all structures located less than 15 ft above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5-10 miles (8-16 km) of the shoreline may be required. Only 3 Category Five Hurricanes have made landfall in the United States since records began: The Labor Day Hurricane of 1935, Hurricane Camille (1969), and Hurricane Andrew in August, 1992. The 1935 Labor Day Hurricane struck the Florida Keys with a minimum pressure of 892 mb--the lowest pressure ever observed in the United States. Hurricane Camille struck the Mississippi Gulf Coast causing a 25-foot storm surge, which inundated Pass Christian. Hurricane Andrew of 1992 made landfall over southern Miami-Dade County, Florida causing 26.5 billion dollars in losses--the costliest hurricane on record. In addition, Hurricane Gilbert of 1988 was a Category Five hurricane at peak intensity and is the strongest Atlantic tropical cyclone on record with a minimum pressure of 888 mb.


the NHC has Katrina at a CAT 3 Storm Surge with a CAT 3 ranges from 9-12 ft above normal her storm surge was well above CAT 5 status with a 30-35 ft storm surge Miami we have a problem with the Saffir Simpson Scale.

[wxmann_91]

the SS scale used to be based upon pressure, until Dr Sheets became NHC director, when wind became the determinant.

Major problems as Gloria was a 942mb cat 3 at Hatteras, even though Hat sustained little damage from a 90KT cat 2 passing to the east, and Long Island did not receive cat 3 damage. We also had 90KT cat 4's. That method created more problems than it solved

I see. Well I had never known that. Thanks for the info Derek.

[Derek Ortt]

those surge heights really only apply to the south Florida area, not the rest of the coast