Hrcn Katrina report from Gary Padgett

[senorpepr]

HURRICANE KATRINA
(TC-12)
23 - 31 August
-------------------------------------

A. Introduction and Storm Origins
---------------------------------

Hurricane Katrina was responsible for what will likely be recorded
as the worst natural disaster in the history of the United States when it
made landfall in extreme southeastern Louisiana and western Mississippi
on the morning of 29 August. A storm surge estimated at up to 10.7 m
(35 ft) obliterated much of the signs of civilization along the coast
of Mississippi, and the resurging waters of Lake Pontchartrain after
the storm had passed broke through levees protecting New Orleans and
left up to 80% of that large city flooded with waters exceeding 6 m
(20 ft) in places. Very severe surge-related damage was also inflicted
on communities along the north shore of the large lake, including
Slidell, Louisiana. Some estimates of the economic impact of Katrina
reported in the media have exceeded $200 billion, well over twice the
damage from Hurricane Andrew and the four hurricanes of 2004 combined.
As of the time of this writing, the death toll stands at well over
1200, by far the deadliest U. S. hurricane since the great Palm Beach
and Lake Okechobee hurricane of 1928.

A tropical wave which left the coast of Africa in early August began
to show some signs of life late on 11 August when it was located about
1300 nm east of the Windward Islands. An associated low-pressure area
formed on the 12th and convection began to slowly increase as the day
progressed. By midday on 13 August satellite images indicated that a
tropical depression appeared to be forming, and advisories on Tropical
Depression 10 were initiated at 2100 UTC, placing the center about
950 nm east of the Lesser Antilles. Environmental conditions quickly
became unfavorable, however, as an unusually deep upper-level trough
developed to the west, and vertical shear had weakened the cyclone so
much that advisories were discontinued the next day. Over the next
week or so the remnants of TD-10 continued westward, occasionally
developing some convection but never really showing any signs of
redevelopment. By the afternoon of 20 August another westward-moving
tropical wave seemed to have caught up with the remnants of TD-10, and
cloudiness and showers extended from the Bahamas eastward for several
hundred miles, the heaviest concentration being north of Puerto Rico.

For the next couple of days the convective activity remained
disorganized, but by the morning of 23 August convection was becoming
more concentrated near the southeastern Bahamas. A Special Tropical
Disturbance Statement was issued by TPC/NHC at 23/1835 UTC, indicating
that a tropical depression was forming within the area of disturbed
weather. There was a debate at NHC regarding whether to re-designate
this depression as TD-10, or to give it a new number. Since the old
TD-10 LLCC had dissipated and another tropical wave had been a player,
it was decided to number the new depression as TD-12.


B. Track and Intensity History
------------------------------

The tropical cyclone initially moved northwestward through the
western Bahamas, passing east of Nassau and west of Eleuthera Island
as it headed for a weakness in the Bermuda HIGH near the southeastern
U. S. coast. Gradual development ensued, and the depression was upgraded
to Tropical Storm Katrina in a special update issued at 1205 UTC on
24 August while located about 60 nm southeast of Nassau. The upgrade
was based on satellite imagery, Doppler radar data from the Bahamas, and
an 1153 UTC reconnaissance 925-mb FLW of 48 kts in the northeast
quadrant. Katrina continued moving northwestward until it reached the
26th parallel. At that point it turned abruptly westward as the weakness
in the HIGH was replaced by a developing ridge. The cyclone continued
to steadily intensify, becoming much better developed by the morning of
25 August. Katrina was upgraded to a hurricane in a special update
issued at 25/1935 UTC, based on NOAA reconnaissance Stepped-Frequency
Microwave Radiometer (SFMR) reports of surface winds of 64 kts as well
as NOAA-Miami Doppler radar velocities of 90 kts at 915 metres. The
storm at this time was centered only about 30 nm east-northeast of
Ft. Lauderdale, Florida, and moving westward at 5 kts.

The eye of Hurricane Katrina made landfall around 25/2300 UTC between
Hallandale Beach and North Miami Beach with the MSW estimated at 70 kts.
Shortly before reaching the coast, the cyclone turned to a west-
southwesterly heading which it followed across the extreme southern
portion of the peninsula, emerging into the Gulf of Mexico around 0700
UTC on 26 August at a point approximately 40 nm south-southeast of Marco
Island. Katrina had weakened to 60 kts crossing the southern tip of
Florida, but it quickly regained hurricane intensity--by 0900 UTC the
cyclone had been re-upgraded to hurricane status, and by early afternoon
Katrina was a Category 2 hurricane sporting 85-kt winds. The unusual
west-southwesterly motion continued through about 0600 UTC on the 27th,
at which time Katrina was located about 115 nm west of Key West, or about
390 nm southeast of the mouth of the Mississippi River. The motion
toward the southwest was apparently due to a very strong deep-layer mean
HIGH centered over Texas, but this feature was forecast to move westward
and leave a weakness over the central Gulf of Mexico.

Katrina was upgraded to a Category 3 hurricane with 100-kt winds at
27/1500 UTC, based on Dvorak intensity estimates ranging from 102 to
115 kts, plus a central pressure of 940 mb measured at 0932 UTC. The
peak FLW measured by the aircraft was 106 kts--somewhat lower than would
normally be expected for a 940-mb hurricane. Katrina's intensification
was halted by an eyewall replacement cycle which began during the morning
of the 27th. The MSW remained pegged at 100 kts for 18 hours while the
CP rose as high as 950 mb before beginning to slowly fall once more.
Very early on 28 August a reconnaissance plane found peak 700-mb winds
of 137 kts in the northwestern eyewall, along with a corresponding CP of
935 mb. Katrina was upgraded to a Category 4 hurricane with a MSW of
125 kts in a special advisory issued at 28/0600 UTC. Not only was
Katrina intensifying, its wind field was expanding also. Hurricane-force
winds now covered an area over 100 nm in diameter while gales covered
an area 240 nm across. The hurricane at this time was located about
270 nm south-southeast of the mouth of the Mississippi River, moving
west-northwestward at 7 kts.

The dangerous Katrina continued to intensify. By 28/0921 UTC the CP
had fallen to 915 mb, and to 910 mb by 1104 UTC. A reconnaissance air-
craft measured a 700-mb FLW of 153 kts, so another special advisory was
issued at 1200 UTC upgrading Katrina to a 140-kt Category 5 hurricane on
the Saffir/Simpson scale. A CP of 907 mb was measured at 1417 UTC along
with a peak FLW of 166 kts. Katrina's MSW was upped to its peak value of
150 kts in the regular 1500 UTC advisory. The minimum CP of 902 mb was
first measured at 1755 UTC and remained there for at least the next two
hours. This 902-mb pressure ranked Katrina as the fourth most intense
Atlantic hurricane on record, based on central pressure, after Gilbert,
1988 (888 mb), the Labor Day storm of 1935 (892 mb), and Allen, 1980
(899 mb). However, this was to be pushed back to 5th place in less
than a month as Hurricane Rita's CP dipped to 897 mb, and further to
6th place in late October as Hurricane Wilma bottomed out at 882 mb.

Even though Katrina's pressure continued to fall a few millibars after
the MSW had reached 150 kts, the intensity was scaled back slightly to
145 kts in the 28/2100 UTC advisory. The explanation given was that
data from the SFMR instrument on board the aircraft suggested that the
700-mb flight level to surface wind reduction ratio might not be quite
as large as the 90% value typically used for eyewall winds. However,
the TPC/NHC monthly summary for August lists the peak MSW for Katrina
as 150 kts, so it will be interesting to see what Katrina's peak MSW
is after post-storm analysis. The next discussion (at 29/0300 UTC)
raises some questions about the performance of the SFMR at such high
wind speeds, so perhaps 150 kts will stand as Katrina's peak MSW. At
2100 UTC on the 28th, the center of this large, extremely dangerous
hurricane was located approximately 130 nm south of the Mississippi
River's mouth, moving toward the northwest at 11 kts.

By 29/0000 UTC Katrina's motion had become more north-northwestward,
and by 0700 UTC the storm was headed due north at 10 kts toward the
Louisiana coast. After peaking in intensity on the afternoon of the
28th, Katrina began to slowly weaken, due in part to eyewall dynamics
and also due to some dry air entrainment on the western side. The
center of Katrina made landfall in Plaquemines Parish around 1200 UTC
on 29 August with a CP of 921 mb and MSW of 120 kts. Hurricane-force
winds covered an area 170 nm in diameter and gales extended across an
area almost 400 nm in diameter. Continuing northward, Katrina made a
second landfall near the Louisiana/Mississippi border around 1500 UTC
with the MSW estimated at 110 kts. As the storm continued northward
through Mississippi, it began to weaken rather rapidly. Winds were
down to 85 kts by 1800 UTC, and Katrina was downgraded to a 55-kt
tropical storm at 30/0000 UTC when located about 50 km (30 miles)
northwest of Meridian, Mississippi. The former Category 5 hurricane
continued to weaken as it moved north-northeastward, becoming a
tropical depression near Clarksville, Tennessee, at 30/1500 UTC. By
the afternoon of 31 August the remnants of Katrina were racing east-
northeastward near Binghamton, New York.

A graphic displaying the track of Hurricane Katrina may be found at
the following link:


<http://www.tropicalcyclone2005.com/database/tc_besttracks_graphics/ATLANTIC
_NORTH/2005_12L_KATRINA.jpg>

Another graphic depicting a zoom-in of the track across Florida to
the northern Gulf Coast landfall may be found at:


<http://www.tropicalcyclone2005.com/database/tc_besttracks_graphics/ATLANTIC
_NORTH/2005_12L_KATRINA_ZOOM.jpg>


C. Meteorological Observations
------------------------------

(1) Wind Observations
---------------------

During Katrina's traversal of South Florida, the highest wind gusts
located by the author was a gust to 76 kts at NHC and a gust of 70 kts
at Tamiami Airport.

As Katrina neared its landfall in Louisiana, Grand Isle reported
sustained winds to 76 kts, gusting to 99 kts, in the hour ending at
29/1000 UTC. During the same hour a Florida Coastal Monitoring Program
wind tower in Galliano, Louisiana, reported sustained winds of 69 kts
with gusts to 87 kts. Between 1000 and 1100 UTC the New Orleans Lake-
front Airport reported a sustained wind of 49 kts with a gust to 74 kts.
The Naval Air Station in Belle Chasse, Louisiana, reported sustained
winds of hurricane force with a peak gust of 83 kts. During the
following hour this station reported a gust of 91 kts.

Between 1300 and 1400 UTC the Pascagoula, Mississippi Civil Defense
Office reported a gust of 103 kts, and the Gulfport Emergency Operations
Center reported sustained winds of 82 kts with a peak gust of 87 kts.
Farther from the center, Dauphin Island, Alabama, reported peak sustained
winds of 66 kts with a gust to 89 kts. Mobile reported a peak gust of
72 kts, and Pensacola, Florida, reported sustained winds of 45 kts with
a gust to 60 kts.

There was a report circulating that a gust of 117 kts had been
recorded at Slidell, Louisiana, but Scott Spratt of the Melbourne NWS
office, who was detailed to the NWS office in Slidell for Katrina's
landfall, states that the 117-kt report was erroneous. Scott did
indicate that a peak gust of 99 kts was recorded at mid-lake on the
Pontchartrain Causeway, but the elevation was unknown.

(2) Rainfall Observations
-------------------------

There was initially a report of 840 mm in 20 hours at a location in
the Everglades in southern Florida, but according to David Roth of HPC,
this was later discounted as it was out of tolerance with other reliable
reports in the area. The peak storm-related rainfall available to the
author from southern Florida was 415 mm near Perrine, located between
Miami and Homestead.

HPC's Katrina rainfall report can be accessed at the following link:

<http://www.hpc.ncep.noaa.gov/tropical/rain/katrina2005rain.gif>

In the Bahamas, Katrina caused a 24-hour rainfall of 100.9 mm at the
Nassau Airport (WMO 78073, 25.1N/77.5W) between 25/1200 and 26/1200 UTC.

In Cuba, Bahia Honda in Pinar del Rio Province (WMO 78318, 22.9N/
83.2W) reported a peak 24-hourly total of 147.3 mm between 27/0000 and
28/0000 UTC. Some locations in the province experienced between 200
and 300 mm of storm total rainfall as Katrina passed westward to the
north of Cuba.

The remnants of Katrina were responsible for some significant rains
in the Canadian Province of Quebec. Charlevoix (WMO 71319, 47.3N/70.6W)
reported a peak 24-hourly total of 177.8 mm between 31/0600 and 01/0600
UTC on 1 September. Several other locations logged over 100 mm of rain
associated with Katrina.

(3) Surge Observations
----------------------

Bill McCaul relates in an e-mail that well-known storm chaser Tim
Marshall made a preliminary ground-level survey of the devastated areas
along the Mississippi coast. Mr. Marshall estimated that the surge
reached 5.5 m (18 ft) in Pascagoula, 6.1 m (20 ft) in Ocean Springs,
6.4 m (21 ft) in Biloxi, 7.0 m (23 ft) in Gulfport, 7.9 m (26 ft) in
Long Beach-Pass Christian (essentially equal here to Hurricane Camille's
surge), 8.5 m (28 ft) in Bay St. Louis, and 9.8 m (32 ft) in Waveland.
The NWS Slidell also performed some surveying in Hancock County, MS,
and estimate that the maximum storm surge may have reached 10.7 m (35 ft)
in Waveland. This is based on the fact that the Hancock County Emergency
Operations Center is at an elevation of 30 ft, and personnel reported
wading through chest-deep water while evacuating.

Pat Fitzpatrick reported that the surge in Slidell, LA, along the
northeastern shore of Lake Pontchartrain was between 6.1 and 7.6 m
(20-25 ft). In one instance a two-story apartment with a base about
8 ft in elevation showed a waterline near the roof. Mr. Fitzpatrick
also noted that the twin-span Interstate 10 bridge across the lake
resembled a jig-saw puzzle.

(4) Miscellaneous
-----------------

Rich Henning, a member of the 53rd Weather Reconnaissance Squadron
(the Hurricane Hunters) reports that the crew on a NOAA reconnaissance
mission measured an eye temperature of 29 C, which may be a record warm
eye measurement for the Atlantic basin. A few Western Pacific super
typhoons have been found to have eye temperatures of 30 and 31 deg C.


D. Storm Effects
----------------

Everyone around the globe who has access to the international cable
TV news channels saw many, many pictures of the indescribable destruction
wrought by Katrina. The damage and casualty figures quoted in the
introductory paragraph are preliminary--it will likely be months before
an accurate death toll is known, and the overall economic effects of
Katrina, including direct damage, recovery costs, upped gas prices,
increased insurance rates, loss of tourism dollars, etc may never be
accurately known.

In the 1960s, the two great north-central Gulf Coast hurricanes of
of that decade, Betsy and Camille, were the first two U. S. hurricanes
to cause direct damages in excess of $1 billion, in terms of current
dollar values. These two storms have become legendary in the annals
of Gulf Coast hurricane history. Betsy struck southeastern Louisiana,
the eye passing very near Grand Isle and later just south and west
of New Orleans. Camille's eye moved northward just east of the
Mississippi River delta and made landfall along the western Mississippi
coastline, the eye passing over Clermont Harbor, Waveland and Bay St.
Louis. Katrina combined the worst effects of both those famous storms
and far exceeded them. Betsy reportedly flooded 20% of New Orleans;
Katrina left 80% of the Crescent City under water. Camille obliterated
much of southern Mississippi with a storm surge ranging from 11.2 feet
at Pascagoula to 24.2 feet at Pass Christian; Katrina obliterated even
more with a surge ranging from an estimated 18 feet at Pascagoula to
35 feet at Waveland.

With all the focus on the catastrophe in Louisiana and Mississippi,
it is easy to overlook the fact that Katrina hit southern Florida with
a pretty good punch. There are 11 confirmed deaths from the storm
during its passage across the southern Florida Peninsula with about
half of these involving falling trees. There have been reports in
the media about many Floridians in Katrina's path not taking the
storm perhaps as seriously as they should nor seeking appropriate
shelter. A lesson to be learned from Katrina in south Florida is that
even a Category 1 hurricane is capable of easily bringing down trees
and persons should not be out in the open or driving in their cars
unless it is absolutely necessary.

(Report written by Gary Padgett)

[senorpepr]

I should state that all the above information is considered "unofficial." The NHC is the official regional specialized met center.