[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 311802
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT TUE 31 AUG 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
1745 UTC.

...SPECIAL FEATURES...

HURRICANE FRANCES IS CENTERED NEAR 20.3N 65.0W...OR ABOUT
140 MILES/230 KM NORTH-NORTHEAST OF SAN JUAN PUERTO RICO...AT
31/1800 UTC. IT IS MOVING WEST 13 KT AROUND THE SOUTHERN
PERIPHERY OF THE SUBTROPICAL RIDGE. MAXIMUM SUSTAINED WIND
SPEED IS MEASURED BY RECON AT 140 MPH/225 KM/HR WITH HIGHER
GUSTS...AND THE RECON MEASURED MINIMUM CENTRAL PRESSURE IS 942
MB. SEE THE LATEST NHC PUBLIC ADVISORY OR FORECAST/ADVISORY
ISSUED UNDER AWIPS/WMO HEADERS MIATCPAT1/WTNT31 KNHC OR
MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS AND WARNING INFORMATION.
SATELLITE IMAGERY SHOWS EXCELLENT UPPER OUTFLOW AND LITTLE
VERTICAL SHEARING. THE EYE IS 27 NM DIAMETER AT THE MOMENT...
AND IS EXPECTED TO UNDERGO THE NORMAL EYEWALL FLUCTUATIONS...
RESULTING IN SLIGHT CHANGES IN INTENSITY ALONG ITS WESTWARD
TRACK...WITH AN OVERALL INCREASE IN INTENSITY TO 125 KT EXPECTED
DURING THE NEXT 24 HOURS...THEN LITTLE CHANGE IN INTENSITY
THROUGH LANDFALL SOMEWHERE ON THE SE COAST CONUS. NUMEROUS
STRONG CONVECTION NOTED WITHIN 115 NM NE SEMICIRCLE AND WITHIN
90 NM OVER THE
SW SEMICIRCLE.

TROPICAL STORM GASTON WAS CENTERED NEAR 39.5N 71.9W OR ABOUT
155 MILES/250 KM...SOUTHEAST OF NANTUCKET MASSACHUSETTS AT
31/1500 UTC. GASTON IS MOVING TOWARD THE NORTHEAST NEAR 18 KT.
MAXIMUM SUSTAINED WINDS ARE 35 KT WITH GUSTS TO 45 KT AND THE
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1001 MB. SEE THE LATEST
NHC ADVISORIES ISSUED UNDER AWIPS/WMO HEADERS MIATCPAT2/WTNT32
KNHC OR MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS.  CONVECTION
CONCENTRATED WITHIN 90 NM OF CENTER OVER N SEMICIRCLE.

...TROPICAL WAVES...

TROPICAL WAVE FROM 8N-20N ALONG 27W HAS A 1014 MB LOW NEAR
18.5N. THE WAVE IS MOVING WESTWARD NEAR 20 KT. THE LOW IS
ACCOMPANIED BY SCATTERED MODERATE TO STRONG CONVECTION WITHIN
90 NM OF CENTER...BUT CURRENTLY LACKS A CONSISTENT BANDING
FEATURE THUS THE UPGRADE TO DEPRESSION STATUS HAS NOT OCCURRED.
THE SURROUNDING ENVIRONMENT REMAINS FAVORABLE FOR DEVELOPMENT
AND TROPICAL DEPRESSION FORMATION IS POSSIBLE DURING THE NEXT
36 HOURS.

CENTRAL ATLANTIC OCEAN TROPICAL WAVE APPROXIMATELY 650 NM
E OF BARBADOS ALONG 48W SOUTH OF 17N MOVING WEST 10 TO 15 KT.
NO SIGNIFICANT CONVECTION AT THIS TIME.

...ITCZ...
ITCZ AXIS IS CENTERED ALONG 10N15W 15N24W 5N44W 8N59W. THE
AXIS PASSES THROUGH A CYCLONIC SWIRL ACCOMPANIED BY SCATTERED
MODERATE AND ISOLATED STRONG WITHIN 90 NM OF 10N19W. THIS SWIRL
IS LIKELY THE AXIS OF A TROPICAL WAVE...BUT WAITING FOR PASSAGE
THROUGH CAPE VERDE ISLANDS FOR UPPER AIR SOUNDING AND MORE
ACCURATE PLACEMENT OF AXIS.

ISOLATED MODERATE AND STRONG ELSEWHERE WITHIN 150 NM OF ITCZ
AXIS BETWEEN 27W-50W BECOMING MORE WIDESPREAD BETWEEN 52W-59W.

...DISCUSSION...

THE GULF OF MEXICO...

AT THE LOW LEVELS A STATIONARY FRONTAL TROUGH EXTENDS FROM THE
FLORIDA PANHANDLE TO THE CENTRAL TEXAS COAST WITH A TROUGH
EXTENDING FROM 29N91W TO 22N95W. AN UPPER LEVEL TROUGH EXTENDS
ALONG 31N92W TO BASE AT 23N92W. MODERATE TO STRONG UPPER
SUBSIDENCE NOTED W OF THIS TROUGH SUPPRESSING CONVECTION ALONG
THE SURFACE TROUGH TO A FEW ISOLATED CELLS. E OF THE TROUGH AXIS
UPPER DIFFLUENCE IS ENHANCING WIDELY SCATTERED SHOWERS AND TSTMS
EASTWARD TO ABOUT 88W. ANOTHER AREA OF SCATTERED SHOWERS/TSTMS
IS LOCATED ALONG THE COAST OF MEXICO FROM VERACRUZ TO TAMPICO.

A NEARLY STATIONARY MID/UPPER LEVEL ANTICYCLONE IS LOCATED NEAR
31N82W WITH A RIDGE EXTENDING SW TO NEAR 23N86W. THE SOUTHERN
END OF THE RIDGE IS BEING ERODED BY A RETROGRADING UPPER LEVEL
LOW CENTERED NEAR 21N88W. UPPER DIFFLUENCE SE OF THE UPPER RIDGE
IS SUPPORTING WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS OVER
THE SE GLFMEX AND FLORIDA KEYS.

CARIBBEAN SEA...
BROAD UPPER LEVEL CYCLONIC ROTATION CONTINUES OVER THE NW
CARIBBEAN IN ASSOCIATION WITH AN UPPER LOW NEAR 21N88W. ONLY A
FEW SHOWERS NOTED MAINLY NEAR THE SW COAST OF CUBA.

ISOLATED SHOWERS AND TSTMS NOTED OVER N CENTRAL CUBA IN
ASSOCIATION WITH AN UPPER LOW OVER THE BAHAMAS NEAR 24N78W.
ELSEWHERE...MODERATE SUBSIDENCE AND DRY AIR PREVAILS S OF 18N E
OF E OF 82W. SCATTERED MODERATE TO STRONG CONVECTION NOTED SW
OF  LINE 15N82W 11N75W.

SUBTROPICAL ATLANTIC OCEAN...
MID-LEVEL RIDGING CONTINUES TO DOMINATE MUCH OF THE ATLC
FORECAST AREA WITH SEVERAL EMBEDDED CYCLONIC SWIRLS. THE MOST
NOTED OF COURSE IS HURRICANE FRANCES. ANOTHER UPPER
CYCLONE...400 NM IN DIAMETER...IS ALONG THE W PERIPHERY OF THE
ATLC RIDGE NEAR 24N78W. THE CYCLONE IS RETROGRADING W AT ABOUT
10 KT...POSSIBLY CONTRIBUTING SLIGHTLY TO FRANCES STEERING N OF
DUE W ATTM. ASSOCIATED INSTABILITY SUPPORTED CONSIDERABLE
CONVECTION LATE LAST NIGHT AND EARLY THIS MORNING...BUT IS
SUPPRESSED AT THE MOMENT...PERHAPS ANOTHER FLARE UP IS IN STORE
WITH PEAK HEATING THIS AFTERNOON.

UPPER ANTICYCLONE NEAR 31N79W HAS A NARROW NE-SW RIDGE ENHANCING
SHOWERS AND A FEW TSTMS NW OF LINE 28N79W 31N78W.

A MID-OCEANIC TROUGH IS DIGGING SW ALONG 35N11W 32N30W THROUGH
AN UPPER CYCLONE AT 23N45W WITH THE TROUGH CONTINUING SW TO
ANOTHER SMALL UPPER TROPICAL CYCLONE AT 11N45W. ONLY ISOLATED
SHOWERS/TSTMS ARE NOTED...MOSTLY WITHIN 360 NM OF THE CYCLONE AT
23N45W. AT THE SURFACE...SUBTROPICAL RIDGE LIES N OF THE AREA
OVER THE CENTRAL TO E ATLC THEN EXTENDING SWD FROM BERMUDA TO
CENTRAL FLORIDA.

TROPICAL ATLANTIC...
ASIDE FROM HURRICANE FRANCES...THE MID ATLC UPPER TROUGH
EXTENDING S INTO THE TROPICS HAS SUPPRESSED CONVECTION ALONG THE
ITCZ TO S OF 11N W OF 35W. A SMALL UPPER CYCLONE AT 15N33W HAS
ENHANCED CONVECTION WITHIN 180 NM OVER ITS NW SEMICIRCLE.

$$
NELSON


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