[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 021743
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU 02 SEP 2004

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
1715 UTC.

...SPECIAL FEATURES...

CATEGORY FOUR HURRICANE FRANCES CENTER NEAR 23.8N 74.4W NEAR
SAN SALVADOR ISLAND IN THE BAHAMAS. THIS POSITION IS ALSO ABOUT
410 MILES/ 660 KM EAST-SOUTHEAST OF THE LOWER FLORIDA COAST
AT 02/1800 UTC...MOVING WEST-NORTHWEST 11 KT. MAXIMUM SUSTAINED
WIND SPEED 125 KT/145 MPH WITH HIGHER GUSTS. ESTIMATED MINIMUM
CENTRAL PRESSURE MEASURED BY RECONNAISSANCE AIRCRAFT IS 949 MB.
SEE LATEST NHC PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS
MIATCPAT1/WTNT31 KNHC AND THE FORECAST/ ADVISORY UNDER HEADERS
MIATCMAT1/WTNT21 KNHC FOR ADDITIONAL INFORMATION. SQUALLS ARE
POUNDING THE CENTRAL AND SOUTHERN BAHAMAS WITH FEEDER BANDS
MOVING ONSHORE NE CUBA...MOVING SE THROUGH THE WINDWARD
PASSAGE...AND OVER NW HAITI. THE NW BAHAMAS WILL EXPERIENCE THE
FIRST SQUALLS EARLY THIS AFTERNOON WITH INCREASING FREQUENCY AND
CONTINUING THROUGH TONIGHT. THE EYE WALL IS FLUCTUATING BETWEEN
20-25 NM DIAMETER THIS MORNING...WITH ASSOCIATED FLUCTUATIONS IN
INTENSITY EXPECTED TILL LANDFALL. UPPER OUTFLOW FROM FRANCES
EXTENDS FROM 15N-32N BETWEEN 78W-65W. IMMEDIATELY TO THE NW OF
THIS ANTICYCLONE AN UPPER TROUGH CONTINUES ALONG 32N73W 29N78W
25N81W ACCOMPANIED BY STRONG UPPER LEVEL SUBSIDENCE WITHIN 90 NM
EITHER SIDE OF TROUGH AXIS. THIS SUBSIDENCE IS INHIBITING
CONVECTION OVER THE NW BAHAMAS AND MAINLAND FLORIDA S OF A CAPE
CANAVERAL-TAMPA BAY LINE AND HOPEFULLY ASSISTING IN HURRICANE
PREPARATIONS BY PUBLIC...MARINE...AND AVIATION INTERESTS IN THE
WATCH/WARNING AREA.

...TROPICAL WAVES...

A 1012 MB LOW PRESSURE IS CENTERED NEAR 10N26.5W ASSOCIATED WITH
A TROPICAL WAVE EXTENDING ALONG 2N27W 15N25W. MOVEMENT OF THIS
SYSTEM IS WEST ESTIMATED AT 15 KT. THREE TENTHS MEASURED BANDING
OF SCATTERED MODERATE TO STRONG CONVECTION THAT IS CURRENTLY
FLARING..AND GOOD OUTFLOW OVER THE W SEMICIRCLE CONTINUES TO
INDICATE THAT A TROPICAL DEPRESSION MAY BE FORMING.

A 1014 MB LOW PRESSURE CENTER IS NEAR 19N41W...ALONG THE N
EXTENSION OF A TROPICAL WAVE EXTENDING SOUTH TO 11N41W. MOVEMENT
OF THE SYSTEM IS WEST ESTIMATED AT 15 KT. SCATTERED MODERATE AND
ISOLATED STRONG SHOWERS AND THUNDERSTORMS ARE OBSERVED WITHIN
420 NM OVER THE NE QUADRANT OF THE LOW PRES...BUT ABOUT 90 NM
OUT FROM THE ESTIMATED LOW LEVEL CENTER OF CIRCULATION. THIS HAS
POSTPONED THE UPGRADE TO A DEPRESSION. ALSO SW UPPER LEVEL SHEAR
CONTINUES W OF THIS SYSTEM. ALTHOUGH TROPICAL CYCLONE
DEVELOPMENT IS STILL POSSIBLE...IT WOULD LIKELY BE A SHORT-LIVED
TROPICAL DEPRESSION.

TROPICAL WAVE ALONG 4N59W 13N59W TO NEAR 24N56W IS MOVING WEST
AT 15 KT. A MOSTLY MID LEVEL CYCLONIC CIRCULATION CENTER IS NEAR
26N47W WITH BROAD CYCLONIC CIRCULATION NOTED FROM 12N-24N
BETWEEN 62W-42W ACCOMPANIED BY WIDELY SCATTERED MODERATE
CONVECTION. FURTHER TO THE SOUTH...THE WAVE IS ENHANCING
ITCZ-RELATED SHOWERS AND THUNDERSTORMS CURRENTLY MOVING ON THE
COAST OF SOUTH AMERICA FROM 6.5-10.5N...AND ACROSS TRINIDAD AND
TOBAGO.

...ITCZ...

ITCZ LIES ALONG 3N9E 5N14W TO LOW PRES NEAR 10N27W...THEN DIPS
SOUTH ALONG 8N30W AND CONTINUES W ALONG 8.5N TO 9N61W. ISOLATED
CONVECTION NOTED WITHIN 120 NM OF AXIS E OF 21W AND BETWEEN 45W
AND 53W...WITH CONVECTION BECOMING MORE WIDESPREAD BETWEEN 29W
AND 41W.

...DISCUSSION...

GULF OF MEXICO...
A DEEP LAYERED TROUGH EXTENDS SOUTH INTO THE GULF ALONG 31N89W
25N91W THROUGH AN UPPER CYCLONE AT 19N92W WITH THE TROUGH
CONTINUING S INTO THE EAST-PACIFIC THROUGH 10N92W. AT THE LOW
LEVELS THE TROUGH IS ANALYZED ALONG 31N84W 24N90W 17N92W.
ASSOCIATED UPPER SUBSIDENCE IS SUPPRESSING CONVECTION TO
ISOLATED MODERATE AT BEST WITHIN 60 NM OF THE DEEP TROUGH AXIS.

TO THE E OF THIS TROUGH...AN UPPER ANTICYCLONE IS NEAR 31N81W
WITH A RIDGE EXTENDING SW ACROSS FLORIDA INTO THE EAST-CENTRAL
GULF OF MEXICO NEAR 27N87W. SMALL UPPER CYCLONES ARE NOTED NEAR
22N85W AND NEAR 20.5N91W...AND ARE BOTH MOVING WEST WITH TIME.
UPPER DIFFLUENCE WITHIN 180 NM OVER THE N SEMICIRCLE OF EACH
UPPER CYCLONE IS ENHANCING WIDELY SCATTERED SHOWERS AND A FEW
THUNDERSTORMS...WHICH ARE MOVING W IN PHASE WITH THE CYCLONES.
ELSEWHERE E OF THE TROUGH WIDELY SCATTERED SHOWERS ARE ENHANCED
ALONG THE WEST PERIPHERY OF THE ANTICYCLONE...ROUGHLY OVER THE
WATERS N OF 24N BETWEEN 84W-88W...AND ARE MOVING
ANTICYCLONICALLY N TO NE AROUND THE STEERING RIDGE.

TO THE WEST OF THE TROUGH...THE UPPER ANTICYCLONE FROM HURRICANE
HOWARD HAS ITS RIDGE EXTENDING NE ACROSS OLD MEXICO ALONG 24N98W
TO A SHARP CREST OVER THE N-CENTRAL GULF AT AT 28N92W. A LARGE
MOISTURE PLUME FROM HOWARD'S CONVECTION IS ADVECTED NE ACROSS SE
TEXAS AND THE NW GULF BEFORE SPILLING SE AROUND THE RIDGE BACK
ACROSS MEXICO W OF 94W. UNDER THIS PLUME...WIDELY SCATTERED
SHOWERS AND A FEW THUNDERSTORMS ARE FLARING AS THEY MOVE
ANTICYCLONICALLY WITH THE MID LEVEL STEERING FROM THE RIDGE.

...THE CARIBBEAN SEA...
EXCEPT AS MENTIONED ABOVE...
UPPER CYCLONES OVER NW CUBA AND OVER THE NW YUCATAN PENINSULA
ARE SUPPORTING UPPER CYCLONIC FLOW OVER THE CARIBBEAN N OF 16N W
OF 83W...ACCOMPANIED BY STRONG UPPER LEVEL SUBSIDENCE.
ELSEWHERE...THE UPPER LEVELS OF THE CARIBBEAN ARE DOMINATED BY
THE UPPER ANTICYCLONE FROM HURRICANE FRANCES...WITH STRONG UPPER
SUBSIDENCE SUPPRESSING CONVECTION. DEBRIS MOISTURE FROM
HURRICANE FRANCES COVER THE REGION NORTH OF 16N BETWEEN
67W-77W.

...THE SUBTROPICAL ATLANTIC...
EXCEPT AS MENTIONED ABOVE...
AN UPPER LEVEL TROUGH LIES NEARLY STATIONARY ALONG 32N4E 27N18W
THEN EXTENDS NW TO AN UPPER CYCLONE AT 33N35W WHICH IS MOVING NE
WITH TIME. THIS TROUGH IS IDENTIFIED BY MODERATE TO STRONG UPPER
SUBSIDENCE WITHIN 120 EITHER SIDE OF TROUGH AXIS. THE TROUGH
CONTINUES SW FROM THE UPPER CYCLONE AT 33N35W TO ANOTHER CYCLONE
AT 27N49W TO YET ANOTHER CYCLONE AT 20N56W. IMMEDIATELY TO THE
SE OF THESE TWO CYCLONES AND UPPER ANTICYCLONE IS NOTED NEAR
23N31W AND IS ABOUT 600 NM DIAMETER.  A SMALL AREA OF UPPER
SUBSIDENCE IS SHIFTING OFF THE AFRICAN COAST WITHIN 120 NM EACH
SIDE OF LINE 16N22W TO 18N10E.

...THE TROPICAL ATLANTIC..
OTHERWISE...A SMALL UPPER ANTICYCLONE IS NOTED NEAR 7N46W. AN
IMPRESSIVE SQUALL LINE IS MOVING W ACROSS AFRICA ALONG
5E...LIKELY OUR NEXT TROPICAL WAVE.

$$
NELSON


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