[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 271742
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SAT AUG 27 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURE...

HURRICANE KATRINA CENTERED NEAR 24.5N 85.4W...OR 340 NM SE OF
THE MOUTH OF THE MISSISSIPPI RIVER...AT 27/1800 UTC MOVING W 6
KT. MAXIMUM SUSTAINED WIND SPEED IS 100 KT WITH GUSTS TO 120 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 949 MB. SEE 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. VISIBLE IMAGERY SHOWS TWO CONVECTIVE
RINGS AROUND THE EYE OF KATRINA...WHICH INDICATES THAT THE
HURRICANE IS GOING THROUGH AN EYEWALL REPLACEMENT CYCLE. THIS
EVENT USUALLY INDICATES THAT THE HURRICANE WILL SOON STRENGTHEN
AND AIR FORCE RECONNAISSANCE WILL BE ABLE TO CONFIRM THIS LATER
THIS AFTERNOON. THE TWO RINGS ARE LOCATED ABOUT 10 NM AND 40 NM
AWAY FROM THE EYE WITH A NARROW MOAT ABOUT 20 NM FROM THE
CENTER. NUMEROUS MODERATE/STRONG CONVECTION EXTENDS WITHIN 110
NM SW SEMICIRCLE AND 80 NM NE SEMICIRCLE...WITH SCATTERED
MODERATE/STRONG ELSEWHERE FROM 20N-25N BETWEEN 81W-88W. RADAR
IMAGERY FROM KEY WEST FLORIDA SHOWS SOLID RAINBANDS EXTENDING
FROM THE DRY TORTUGAS WWD AND MORE ISOLATED SHOWERS/TSTMS
RUNNING FROM S TO N OVER THE KEYS AND SOUTH FLORIDA. ISOLATED
SHOWERS/TSTMS ARE ALSO NW OF KATRINA FROM 24N-29N BETWEEN
90W-93W. UPPER LEVEL OUTFLOW OVER KATRINA IS BEST OVER ITS E AND
S SEMICIRCLES BUT APPEARS SOMEWHAT LIMITED TO THE N AND W DUE
TO SURROUNDING DRY AIR. KATRINA IS EXPECTED TO STRENGTHEN TO
CATEGORY 4 STATUS AND MAKE LANDFALL ALONG THE N GULF COAST SOME
TIME ON MONDAY. BECAUSE OF THIS...A HURRICANE WATCH HAS BEEN
ISSUED BETWEEN MORGAN CITY LOUISIANA AND THE MOUTH OF THE PEARL
RIVER...INCLUDING NEW ORLEANS AND LAKE PONCHARTRAIN. THIS IS AN
EXTREMELY DANGEROUS SITUATION...AND ALL RESIDENTS ALONG THE
COAST BETWEEN THE FLORIDA PANHANDLE AND FAR EASTERN TEXAS NEED
TO KEEP ABREAST OF THE SITUATION AND FOLLOW THE ADVICE OF LOCAL
GOVERNMENT OFFICIALS AND EMERGENCY MANAGERS.

...TROPICAL WAVES...

...BASED ON UPPER AIR DATA FROM DAKAR...THERE HAVE BEEN 3
TROPICAL WAVE PASSAGES SINCE AUGUST 20TH. TROPICAL WAVE
PLACEMENT ACROSS THE ATLANTIC HAS BEEN ADJUSTED A BIT TO ACCOUNT
FOR THIS DATA.

EAST ATLANTIC TROPICAL WAVE ALONG 38W S OF 18N MOVING W 15 KT
WITH A 1010 MB LOW ALONG THE WAVE NEAR 12N. THIS WAVE WAS
OBSERVED IN THE DAKAR UPPER AIR DATA AROUND 12Z AUG 25...OR
ABOUT 2 DAYS AGO. THE ACTUAL SURFACE REFLECTION OF THE WAVE
APPEARS TO BE LOCATED ALONG 35W...BUT THE STRUCTURE OF THE WAVE
HAS BEEN TILTED WEST WITH HEIGHT SO THE PRESENT POSITION IS A
COMPROMISE OF THE SURFACE AND MID-LEVEL CIRCULATIONS. A BAND OF
SCATTERED MODERATE CONVECTION HAS BEEN FORMING TO THE S/SW OF
THE LOW FROM 9N-13N BETWEEN 37W-44W...WITH ISOLATED TSTMS
ELSEWHERE FROM 7N-17N BETWEEN 32W-45W. NOW THAT THE TSTM
ACTIVITY IS INCREASING IN COVERAGE AND BECOMING MORE
ORGANIZED...THE SYSTEM WILL BE MONITORED FOR DEVELOPMENT OVER
THE NEXT SEVERAL DAYS.

CENTRAL ATLANTIC TROPICAL WAVE ALONG 51W S OF 17N MOVING W 15
KT. THIS WAVE MOVED OFF THE AFRICAN COAST ABOUT 2 DAYS BEFORE
THE WAVE DESCRIBED ABOVE...LATE ON AUGUST 23...AND BY
EXTRAPOLATION THIS GIVES IT A POSITION FARTHER W THAN PREVIOUSLY
CARRIED...UNDERCUTTING THE LOW NEAR 22N54W. ISOLATED TSTMS FROM
16N-20N BETWEEN 48W-53W.

TROPICAL WAVE HAS MOVED INLAND OVER THE YUCATAN PENINSULA AND
GUATEMALA ALONG 89W S OF 19N MOVING W 10-15 KT. A LOW-LEVEL
CIRCULATION IS NOTED S OF EL SALVADOR OVER THE E PACIFIC...WITH
LITTLE SIGNATURE AND NO CONVECTION OVER LAND.

...ITCZ...

ITCZ AXIS IS ALONG 12N14W 11N19W 16N30W...THEN ALONG 10N38W
14N47W...THEN ALONG 16N55W 9N63W. ISOLATED SHOWERS/TSTMS FROM
5N-10N BETWEEN 10W-26W. ISOLATED SHOWERS/TSTMS MOVING WWD
BETWEEN BARBADOS AND TOBAGO AND OVER THE GRENADINES.

...DISCUSSION...

GULF OF MEXICO...
THE CIRCULATION OF HURRICANE KATRINA IS BEGINNING TO ENCOMPASS
THE ENTIRE GULF OF MEXICO...SEE SPECIAL FEATURES FOR MORE INFO.
ASIDE FROM UPPER LEVEL ANTICYCLONE OVER KATRINA...ANOTHER LARGE
ANTICYCLONE IS CENTERED OVER THE W GULF NEAR 23N96W AND IS
ASSOCIATED WITH A LARGE AREA OF DRY AIR...LIMITING THE OUTFLOW
ON THE W SIDE OF THE HURRICANE. LOW-LEVEL MOISTURE WILL BE
FAIRLY LIMITED OVER THE W GULF AS KATRINA LIFTS TO THE N...SO
THE GREATEST COVERAGE OF CONVECTION IS EXPECTED NEAR AND TO THE
E OF THE HURRICANE WITHIN BROAD SOUTHERLY FLOW.

CARIBBEAN...
THE BROAD UPPER LEVEL ANTICYCLONE OVER THE GULF OF MEXICO HAS
EXPANDED SEWD OVER THE W CARIBBEAN...AND BROAD NELY FLOW EXTENDS
W OF 70W. A LARGE CIRRUS CANOPY IS EMBEDDED WITHIN THIS FLOW
RADIATING AWAY FROM KATRINA...AND HAS ALSO SPREAD OVER THE W
CARIBBEAN. SCATTERED MODERATE CONVECTION HAS DEVELOPED S OF
JAMAICA AND HAITI FROM 15N-18N BETWEEN 73W-78W WITH WIDELY
SCATTERED SHOWERS/TSTMS FROM 18N-21N BETWEEN 74W-80W. A SHARP
UPPER TROUGH OVER THE W ATLC EXTENDS SWD ACROSS PUERTO RICO TO
NEAR 15N70W. ISOLATED SHOWERS/TSTMS ARE NEAR THIS FEATURE N OF
14N BETWEEN 64W-70W. AN E/W ORIENTED UPPER RIDGE EXTENDS INTO
THE E CARIBBEAN FROM THE ATLC WATERS ALONG 16N...EXTENDING SW
TOWARDS ARUBA. DRIER AIR IS MOVING IN BENEATH THE RIDGE WITH THE
DEEPEST MOISTURE NEAR THE NRN LEEWARD ISLANDS AND GREATER
ANTILLES. MOISTURE WILL BE ENTRENCHED OVER THE W CARIBBEAN AT
LEAST THROUGH TUE WHICH WILL FOSTER THE POSSIBILITY OF SCATTERED
SHOWERS/TSTMS FOR THE NEXT SEVERAL DAYS W OF 68W.

ATLANTIC...
A WEAK SURFACE TROUGH APPEARS TO BE LIFTING NWD OVER THE W ATLC
WATERS...AND THIS HAS BEEN JUST ENOUGH TO TRIGGER SCATTERED
SHOWERS/TSTMS WITH EMBEDDED ISOLATED MODERATE CONVECTION N OF
22N BETWEEN 69W-78W. SOME OF THESE SHOWERS ARE MEANDERING OVER
THE CENTRAL BAHAMAS BUT MOST OF THE ACTIVITY IS OVER OPEN WATERS
TO THE NE. A SHARP UPPER TROUGH IS ALIGNED ALONG 32N61W TO
PUERTO RICO WITH A WEAK UPPER LOW POSSIBLY CENTERED NEAR 29N62W.
DEEP MOISTURE IS BEING PULLED NWD AHEAD OF THE TROUGH AND WIDELY
SCATTERED MODERATE CONVECTION IS DEVELOPING N OF 26N BETWEEN
46W-60W. FARTHER S...A 1009 MB LOW IS CENTERED NEAR 21N52W
MOVING WNW 10-15 KT. THE LOW IS BEING SHEARED BY THE STRONG SWLY
FLOW AHEAD OF THE TROUGH...AND NUMEROUS MODERATE/STRONG
CONVECTION IS NE OF THE CENTER FROM 20N-26N BETWEEN 48W-52W. THE
UPPER LEVEL ENVIRONMENT IS NOT EXPECTED TO BECOME MORE FAVORABLE
ANY TIME SOON...SO TROPICAL CYCLONE DEVELOPMENT IS NOT
ANTICIPATED OVER THE NEXT SEVERAL DAYS. A LARGE UPPER HIGH IS
CENTERED OVER THE CENTRAL ATLC NEAR 18N49W...WITH STRONG
EASTERLY FLOW PUSHING THE LOW/TROPICAL WAVE ALONG 38W QUICKLY TO
THE W. ELSEWHERE...A LARGE UPPER LOW IS CENTERED 225 NM WNW OF
MADEIRA ISLAND NEAR 34N21W AND EXTENDS SWD INTO THE AREA N OF
28N E OF 30W. AFRICAN DUST IS CURRENTLY LOCATED FROM 10N-27N E
OF 30W...AND FROM 18N-27N BETWEEN 30W-50W.

$$
BERG


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