[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 291157
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT MON AUG 29 2005

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM
THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON
SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND
METEOROLOGICAL ANALYSIS.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1045 UTC.

...SPECIAL FEATURES...

HURRICANE KATRINA IS CENTERED NEAR 29.1N 89.6W AT 29/1100 UTC OR
ABOUT 70 NM SSE OF NEW ORLEANS MOVING N AT 13 KT. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 918 MB. MAXIMUM SUSTAINED WIND SPEED
IS 125 KT WITH HIGHER GUSTS. SEE THE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC
AND THE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT2/WTNT32
KNHC FOR MORE DETAILS. KATRINA IS A CATEGORY FOUR
HURRICANE...BUT IT IS STILL A VERY DANGEROUS HURRICANE. A
WELL-DEFINED EYE AND SYMMETRIC OUTFLOW PATTERN REMAINS ON
SATELLITE IMAGERY. THE LEADING EDGE OF EYEWALL IS MOVING OVER
THE MISSISSIPPI DELTA. HURRICANE FORCE WINDS REACHED THE COAST
BETWEEN 0600 AND 0700 UTC. CONVECTION IS NOT AS SYMMETRICAL AS 6
HOURS AGO. SCATTERED MODERATE/STRONG CONVECTION IS WITHIN 180 NM
IN THE E SEMICIRCLE AND WITHIN 90/120 NM IN THE W SEMICIRCLE.
OUTER RAINBANDS NOW ARE N OF 24N BETWEEN PANAMA CITY FLORIDA TO
CENTRAL LOUISIANA NEAR ATCHAFALAYA BAY.

TROPICAL DEPRESSION THIRTEEN IS OVER THE CENTRAL ATLC AT 29/0900
UTC NEAR 16.8N 49.4W MOVING NW AT 12 KT. ESTIMATED MINIMUM
CENTRAL PRESSURE IS 1007 MB. MAXIMUM SUSTAINED WIND SPEED IS 25
KT WITH GUSTS TO 35 KT. SEE THE LATEST NHC FORECAST/ADVISORY
UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC AND THE PUBLIC
ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT3/WTNT33 KNHC FOR MORE
DETAILS. T.D. THIRTEEN CONTINUES TO BE UNDER SE SHEAR THUS HAS
NOT BECOME BETTER ORGANIZED OVER THE PAST 6 HOURS. SCATTERED
MODERATE/STRONG CONVECTION IS TO THE NW OF THE LOW WITHIN 90/120
NM OF LINE 16N52W-21N49W. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS FURTHER N WITHIN A 75 NM RADIUS OF 23N49W.

E ATLC TROPICAL WAVE IS ALONG 23W S OF 20N WITH A 1008 MB LOW
ALONG THE WAVE NEAR 12N. SATELLITE IMAGERY SHOWS A BROAD
CIRCULATION ASSOCIATED WITH THIS SYSTEM AND SURFACE ANALYSIS
INDICATES LOWER PRESSURES. THIS SYSTEM HAS THE POTENTIAL TO BE A
TROPICAL CYCLONE IN THE NEXT DAY OR TWO. SCATTERED MODERATE/
ISOLATED STRONG CONVECTION IS NW OF THE LOW WITHIN A 75 NM
RADIUS OF 13.5N23.5W INCLUDING THE SOUTHERN MOST ISLANDS OF THE
CAPE VERDES.

...TROPICAL WAVES...
W CARIBBEAN TROPICAL WAVE IS ALONG 62W/63W S OF 17N MOVING W
10-15 KT. WEAK WAVE SIGNATURE CURVATURE IS OBSERVED IN THE LOW
CLOUDS. WAVE IS EMBEDDED WITH VERY DRY AIR...THUS NO ASSOCIATED
SHOWERS/CONVECTION.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 13N16W 12N19W THEN ALONG 10N24W
7N35W 17N44W THEN ALONG 13N49W 9N53W 11N61W. SCATTERED STRONG
CONVECTION IS WITHIN 60 NM OF LINE 9N30.5W-13N31W. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 120 NM OF THE AXIS
FROM 28W-36W AND MOVING OFF AFRICA WITHIN 60 NM OF 7N E OF 15W
TO THE COAST.

...DISCUSSION...

GULF OF MEXICO...
KATRINA DOMINATES THE WEATHER THIS MORNING MAKING LANDFALL ON
THE N GULF COAST NEAR NEW ORLEANS LOUISIANA. SEE SPECIAL
FEATURES ABOVE. IN THE UPPER LEVELS...A LARGE HIGH IS OVER
KATRINA ENHANCING UPPER LEVEL OUTFLOW ESPECIALLY TO THE N AND E
OF THE CENTER. ALL OF BUT THE FAR W GULF W OF 95W IS MOISTURE
LADEN AND EXPECT SHOWERS/ISOLATED THUNDERSTORMS. THE UPPER LEVEL
HIGH WILL BEGIN TO MOVE NE AS KATRINA MOVES FURTHER INLAND.

CARIBBEAN SEA...
DEEP LAYERED EASTERLY FLOW DOMINATES THE CARIBBEAN. THE BROAD
UPPER LEVEL HIGH CENTERED NEAR KATRINA EXTENDS OVER THE NW
CARIBBEAN N OF 15N W OF 70W. OUTFLOW FROM KATRINA IS AIDING THE
CLUSTERS OF SCATTERED SHOWERS/THUNDERSTORMS FROM HAITI OVER CUBA
N OF 18N. SCATTERED MODERATE/STRONG CONVECTION IS FROM 9N-12N
BETWEEN 71W-78W IN ASSOCIATED WITH THE ITCZ. THE E CARIBBEAN IS
UNDER STRONG SUBSIDENCE AND VERY DRY AIR FROM A BROAD UPPER HIGH
OVER THE CENTRAL ATLC.

ATLANTIC OCEAN...
BROAD UPPER HIGH OVER KATRINA COVERS THE W ATLC W OF 68W.
EMBEDDED WITHIN THIS FLOW...IS A SMALL WEAK 1012 MB LOW CENTERED
NEAR 29N96W WITH A SURFACE TROUGH EXTENDING SW TO N BAHAMA
ISLANDS. THIS FEATURE CONTINUES TO WEAKEN BUT IS GENERATING
CLUSTERS OF SCATTERED SHOWERS/ISOLATED THUNDERSTORMS FROM
25N-30N BETWEEN 70W-76W. MID/UPPER TROUGH EXTENDS FROM THE
CENTRAL/W ATLC THROUGH 32N60W TO PUERTO RICO NEAR 17N69W. AN
UPPER SHORTWAVE TROUGH IS EMBEDDED WITHIN THE FLOW ALONG 65W N
OF 29N. THIS SHORTWAVE IS GENERATING SCATTERED MODERATE/ISOLATED
STRONG CONVECTION N OF 29N FROM 60W-66W. A 1012 MB LOW IS ALONG
THE E SIDE OF THE UPPER TROUGH NEAR 23N58W WITH A SURFACE TROUGH
EXTENDING FROM 30N55W THROUGH THE LOW TO 19N59W. ONLY ISOLATED
SHOWERS ARE BEING MAINTAINED DUE TO DRY UPPER AIR. BROAD
MID/UPPER LEVEL HIGH IS IN THE CENTRAL ATLC NEAR 19N50W...NEAR
T.D. THIRTEEN AND COVERS THE AREA BETWEEN THE UPPER TROUGH TO
THE W AND 35W. THIS IS LIMITING CONVECTION WITHIN THE ITCZ W OF
40W. LARGE UPPER LOW IS OVER THE NE ATLC N OF THE REGION AND
EXTENDS INTO THE AREA N OF 25N FROM THE CANARY ISLANDS TO NEAR
35W. SE OF THE CAPE VERDE ISLANDS MOISTURE INCREASES WITH UPPER
RIDGING SUPPRESSING THE ITCZ AND CONVECTION TO THE S.

$$
WALLACE


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