[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 041753
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN SEP 04 2011

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1730 UTC.

...SPECIAL FEATURES...

TROPICAL STORM LEE IS CENTERED NEAR 230.4N 91.8W AT 04/1800 UTC
OR 35 NM WSW OF BATON ROUGE LOUISIANA AND ABOUT 20 NM NE OF
LAFAYETTE LOUISIANA MOVING NNE AT 7 KT. ESTIMATED MINIMUM
CENTRAL PRESSURE IS 987 MB. MAXIMUM SUSTAINED WIND SPEED IS 40
KT WITH GUSTS TO 55 KT. SATELLITE AND LIGHTNING DATA INDICATE
SCATTERED MODERATE/ISOLATED STRONG CONVECTION REMAINS OVER WATER
IN THE SE QUADRANT OF LEE WITH TWO MAIN CONVECTIVE BANDS. THE
INNERMOST BAND EXTENDS FROM NEAR 26N94W TO SRN MISSISSIPPI NEAR
30N90W CONTINUING INLAND AS INDICATED BY DOPPLER RADAR. THE
SECOND...AND BROADER BAND EXTENDS FROM NEAR 23N92W TO THE
FLORIDA PANHANDLE NEAR 30N86W WITH RAINFALL CONTINUING INTO
ALABAMA...GEORGIA...AND MISSISSIPPI. RADAR IMAGERY ALSO
INDICATES SCATTERED SHOWERS/ISOLATED THUNDERSTORMS WITHIN 90 NM
OF THE STORM CENTER WITH THE STRONGEST ACTIVITY NE OF THE
CENTER. SOME ISOLATED SHOWERS ALSO EXTEND TO JUST W OF THE WRN
COAST OF THE FLORIDA PENINSULA. SEE LATEST NHC INTERMEDIATE
PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT3/ WTNT33 KNHC
AND THE FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADER
MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS.

HURRICANE KATIA IS CENTERED NEAR 21.9N 59.2W AT 04/1500 UTC OR
ABOUT 315 NM NE OF THE NORTHERN LEEWARD ISLANDS MOVING NW AT 10
KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 966 MB. MAXIMUM
SUSTAINED WIND SPEED IS 85 KT WITH GUSTS TO 105 KT. OVER THE
PAST SEVERAL HOURS KATIA HAS RAPIDLY INTENSIFIED AND HAS REACHED
CATEGORY 2 STATUS. NUMEROUS STRONG CONVECTION IS AROUND THE SW
SIDE OF THE CENTER FROM 21N-23N BETWEEN 59W-61W. NUMEROUS
MODERATE/ISOLATED STRONG CONVECTION IS ELSEWHERE FROM 20N-25N
BETWEEN 57W-62W. SEE LATEST NHC FORECAST/ADVISORY UNDER
AWIPS/WMO HEADER MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS.

...TROPICAL WAVES...

TROPICAL WAVE IS MOVING WWD AT 10-15 KT ACROSS THE CAPE VERDE
ISLANDS FROM 16N24W TO 10N22W. UPPER AIR TIME SECTION ANALYSES
FROM DAKAR SENEGAL INDICATES THAT THE WAVE MOVED OFF THE COAST
OF AFRICA AROUND 24 HOURS AGO. MOISTURE ASSOCIATED WITH THE WAVE
EXTENDS OVER TO ABOUT 18N WITH HIGHEST VALUES LOCATED IN LOW
LATITUDES AROUND 8N. SCATTERED MODERATE/STRONG CONVECTION IS
MAINLY SW OF THE WAVE FROM 5N-11N BETWEEN 22W-29W.

TROPICAL WAVE EXTENDS FROM 19N41W TO A NEARLY DISSIPATED 1013 MB
LOW NEAR 14N37W. WHILE THERE IS CLEAR CYCLONIC FLOW AROUND THE
WAVE AXIS INDICATED BY AN ASCAT SCATTEROMETER PASS...IT APPEARS
THAT IT HAS OPENED UP INTO A TROUGH WITHOUT A CLOSED CIRCULATION
AROUND THE LOW. GLOBAL MODEL GUIDANCE INDICATES THAT THE WAVE IS
NO LONGER EMBEDDED WITHIN THE MONSOON TROUGH AND MAY DAMPEN OVER
THE NEXT 24-48 HOURS...BUT A DISCERNIBLE FEATURE CAN BE TRACKED
OVER THE NEXT SEVERAL DAYS AND MAY BEGIN TO GAIN A NORTHERLY
COMPONENT IN ITS MOTION. CURRENTLY SCATTERED MODERATE CONVECTION
IS E OF THE WAVE FROM 13N-18N BETWEEN 32W-39W.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 17N16W TO
THE BASE OF A TROPICAL WAVE NEAR 10N22W. DUE TO THE CIRCULATION
OF A TROPICAL WAVE FARTHER W IN THE CENTRAL TROPICAL ATLC...THE
MONSOON TROUGH HAS BROKEN W OF THE WAVE AXIS NEAR THE CAPE VERDE
ISLANDS. AS THE WAVES MOVE WWD...THE MONSOON TROUGH WILL BUILD
BACK IN. THE ITCZ PICKS UP S OF THE CENTRAL TROPICAL ATLC WAVE
ALONG 8N39W TO 5N58W.

...DISCUSSION...

GULF OF MEXICO...
TROPICAL STORM LEE...WITH CENTER NOW INLAND OVER
LOUISIANA...DOMINATES THE MAJORITY OF THE GULF OF MEXICO TODAY.
THE STORM IS FORECAST TO MOVE SLOWLY NE AND WILL LIKELY CONTINUE
TO IMPACT THE BASIN...ESPECIALLY THE ERN HALF...FOR THE NEXT
COUPLE OF DAYS. SEE SPECIAL FEATURES ABOVE FOR MORE DETAILS.
MUCH OF THE PRECIPITATION WITH LEE IS ON THE ERN SIDE OF THE
STORM WITH RAINBANDS IMPACTING THE FLORIDA PANHANDLE...SW
GEORGIA...ALABAMA...MISSISSIPPI...AND LOUISIANA. THE HEAVIEST
RAINFALL ALSO LIES UNDERNEATH AN AREA OF DIFFLUENCE ALOFT
BETWEEN AN UPPER LEVEL TROUGH OVER LEE...AND AN UPPER LEVEL
RIDGE COVERING THE FAR ERN GULF. WITH TOTAL RAINFALL AMOUNTS OF
10-15 INCHES AND MAXIMUM AMOUNTS OF 20 INCHES...FLOODING IS A
MAJOR THREAT FOR MUCH OF THE SE UNITED STATES. REFER TO FLOOD
PRODUCTS AND HURRICANE LOCAL STATEMENTS ISSUED BY LOCAL NWS
FORECAST OFFICES FOR MORE DETAILED INFORMATION ON THESE THREATS.
AS LEE DRIFTS NE...A FRONTAL SYSTEM IS EXPECTED TO MERGE WITH IT
WHICH WILL SWEEP A COLD FRONT THROUGH THE NW GULF. DRY AIR
BEHIND THE FRONT WILL PROVIDE FAIR CONDITIONS IN THE WAKE OF THE
FRONT...WHILE THE ERN HALF OF THE BASIN WILL REMAIN UNDER THE
HIGH MOISTURE VALUES ASSOCIATED WITH LEE.

CARIBBEAN SEA...
MAINLY NELY FLOW ALOFT COVERS THE FAR WRN CARIBBEAN AROUND AN
UPPER LEVEL RIDGE OVER THE ERN GULF OF MEXICO. THIS IS ALSO
DRAWING SOME MOISTURE FROM TROPICAL STORM LEE INTO THIS PORTION
OF THE AREA SUPPORTING SOME ISOLATED PATCHES OF
SHOWERS/THUNDERSTORMS BETWEEN 74W-83W. ACTIVE STORMS ARE
CURRENTLY N AND W OF JAMAICA...ACROSS CENTRAL CUBA...AND NEAR
PANAMA AND COSTA RICA. THE ACTIVITY NEAR CENTRAL AMERICA IS ALSO
ASSOCIATED WITH THE MONSOON TROUGH THAT EXTENDS FROM THE E
PACIFIC ACROSS NICARAGUA TO NRN COLOMBIA. THE ERN CARIBBEAN IS
EXPERIENCING FAIR WEATHER WITH MOSTLY CLEAR SKIES AND NE-E LIGHT
TO MODERATE TRADEWIND FLOW. DRY AIR ALOFT ALSO COVERS THIS
PORTION OF THE BASIN AROUND A WEAK UPPER LEVEL RIDGE CENTER N
OF VENEZUELA NEAR 13N68W. EXPECT LITTLE CHANGE OVER THE NEXT 24
HOURS.

ATLANTIC OCEAN...
THE FAR WRN ATLC IS EXPERIENCING MOSTLY FAIR WEATHER INFLUENCED
BY WEAK SURFACE RIDGING OVER NORTH CAROLINA AND MOSTLY DRY AIR
ALOFT. SOME UPPER LEVEL CLOUDS EXTEND OVER FLORIDA ASSOCIATED
WITH OUTFLOW FROM LEE. A WEAK SURFACE TROUGH ANALYZED AT 1200
UTC NEAR 31N71W TO 28N74W HAS DISSIPATED AS OF 1500 UTC.
SCATTERED SHOWERS/THUNDERSTORMS ARE E OF THIS AREA ALONG A SWATH
FROM 22N75W TO 31N68W ASSOCIATED WITH UPPER LEVEL DIFFLUENCE
AROUND AN UPPER LEVEL TROUGH SITTING OVER THE WRN ATLC ALONG
71W. HURRICANE KATIA IS TO THE E IMPACTING THE CENTRAL ATLC. SEE
SPECIAL FEATURES FOR MORE DETAILS. AN UPPER LEVEL RIDGE TO THE E
OF KATIA NEAR 21N49W IS SUPPORTING A SURFACE RIDGE ANCHORED BY A
1025 MB HIGH NEAR 32N44W. A PAIR OF TROPICAL WAVES ARE IMPACTING
THE CENTRAL AND ERN TROPICAL ATLC. THESE WAVES ARE EXPECTED TO
DRIFT WWD BEFORE GAINING A NLY COMPONENT AND WILL MOVE AROUND
THE SUBTROPICAL RIDGE. AN UPPER LEVEL TROUGH COVERING THE ERN
ATLC FROM 30N26W TO 16N36W IS HELPING ENHANCE CONVECTION NEAR
THE WRN MOST TROPICAL WAVE.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

$$
WALTON




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