[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 261805
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU 26 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
1730 UTC.

...SPECIAL FEATURE...
TROPICAL STORM FRANCES CENTER NEAR 13.1N 45.0W...OR ABOUT 1105
MILES...1775 KM...EAST OF THE LESSER ANTILLES AT 26/1500 UTC.
FRANCES CONTINUES TO MOVE WEST-NORTHWEST AT 15 KT. MAXIMUM
SUSTAINED WIND SPEED HAS INCREASED TO 60 KT WITH TO GUSTS 75 KT
AND THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 990 MB.  SEE THE
LATEST NHC FORECAST/ ADVISORY ISSUED UNDER AWIPS/WMO HEADERS
MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS.  SATELLITE IMAGERY
INDICATES THAT FRANCES HAS BECOME BETTER ORGANIZED DURING THE
LAST SEVERAL HOURS WITH INCREASING CONVECTION NEAR THE CENTER
AND IMPROVING BANDING STRUCTURE.  FRANCES REMAINS NEAR THE W
PERIPHERY OF A MID-UPPER LEVEL RIDGE ALONG 16N/17N WHICH IS
CREATING A FAVORABLE ENVIRONMENT COMPRISED OF LOW SHEAR AND GOOD
OUTFLOW. ACCORDINGLY...FRANCES IS FORECAST TO CONTINUE
STRENGTHENING AS IT MOVES NW.

...TROPICAL WAVES...
TROPICAL WAVE EMERGING OFF THE COAST OF AFRICA ALONG 18W SOUTH
OF 22N MOVING WEST 10-15 KT.  THE WAVE IS NOT WELL DEFINED IN
SATELLITE IMAGERY BUT DID DISPLAY A NICE SIGNATURE IN THE BAMAKO
UPPER AIR TIME SECTION.  WHILE THERE IS VERY LITTLE CONVECTION
NEAR THE WAVE AXIS...A SIGNIFICANT FLARE UP OF ITCZ CONVECTION
HAS OCCURRED AHEAD OF THE WAVE FROM 5N-10N BETWEEN 20W-27W.
SATELLITE ANALYSIS INDICATES A FAIR AMOUNT OF DRY AIR N AND W OF
THE WAVE WHICH COULD LIMIT DEVELOPMENT POTENTIAL.

TROPICAL WAVE OVER THE E CARIBBEAN ALONG 66W SOUTH OF 16N MOVING
WEST 15-20 KT.  THE WAVE REMAINS POORLY DEFINED IN SATELLITE
IMAGERY AND THE POSITION IS BASED ON E CARIBBEAN UPPER AIR DATA
INDICATING PASSAGE YESTERDAY AND LAST NIGHT. THERE IS NO
SIGNIFICANT CONVECTION WITH THE WAVE BUT UW-CIMSS SATELLITE
ANALYSIS INDICATES THAT THE WAVE MARKS THE LEADING EDGE OF SOME
AFRICAN DUST.

...ITCZ...
ITCZ EMERGES OFF THE COAST OF AFRICA NEAR 12N15W WESTWARD ALONG
8N30W 13N40W 10N50W INTO N PORTIONS OF S AMERICA OVER SURINAME
AND GUYANA ALONG 5N57W THEN NW TO PANAMA. AN AREA OF SCATTERED
STRONG CONVECTION IS LOCATED OVER SW CARIBBEAN S OF 15N BETWEEN
77W-84W INCLUDING COASTAL AREAS OF PANAMA AND NICARAGUA.

...DISCUSSION...
THE GULF OF MEXICO...
STRONG MIDDLE TO UPPER LEVEL RIDGING WHICH HAS BEEN IN PLACE
OVER THE GLFMEX DURING THE LAST FEW DAYS IS NOW BEING UNDERCUT
BY A RETROGRADING UPPER LOW OVER S MEXICO AND GUATEMALA. THE
RIDGE NOW EXTENDS ALONG THE NW GLFMEX COAST INTO THE SE UNITED
SATES NEAR LOUISIANA.  NEARLY ALL OF THE UPSTREAM MOISTURE AND
DYNAMICS ARE RIDING UP AND OVER THE RIDGE PRODUCING A
DRY/TRANQUIL PATTERN W OF 90W. ADDITIONALLY CONFLUENT FLOW ON
THE BACKSIDE OF THE RETROGRADING UPPER LOW IS FURTHER
SUPPRESSING SIGNIFICANT CONVECTIVE ACTIVITY OVER S MEXICO AND
THE BAY OF CAMPECHE.  FURTHER N...AN UPPER LEVEL SHORTWAVE
TROUGH OVER N FLORIDA COUPLED WITH A WEAK LOW LEVEL
TROUGH...FROM THE YUCATAN PENINSULA TO N FLORIDA...CONTINUES TO
TRIGGER ENHANCED SHOWER/THUNDERSTORM ACTIVITY OVER MUCH OF
FLORIDA AND GLFMEX E OF 90W.

THE CARIBBEAN SEA...
MID-OCEANIC TROUGH EXTENDS FROM THE CENTRAL ATLC ACROSS THE N
CARIBBEAN OVER HISPANIOLA AND JAMAICA TO AN UPPER LOW OVER
GUATEMALA.  SUBSIDENCE INDUCED DRY AIR COVERS THE AREA N OF THE
TROUGH LIMITING CONVECTIVE ACTIVITY. FURTHER S...MID/UPPER LEVEL
RIDGE EXTENDS FROM COLOMBIA NW TO A POSITION JUST E OF THE
NICARAGUA/HONDURAS BORDER NEAR 15N82W. DIFFLUENT FLOW ALONG THE
RIDGE AXIS COUPLED WITH THE ITCZ OVER PANAMA IS PRODUCING AN
IMPRESSIVE AREA OF SCATTERED STRONG CONVECTION WITHIN 30 NM
EITHER SIDE OF A LINE FROM 10N77W 15N84W. THIS AREA OF ACTIVE
WEATHER SHOULD REMAIN NEARLY STATIONARY FOR THE NEXT 12-24 HOURS
THEN GRADUALLY SHIFT WESTWARD INTO CENTRAL AMERICA AS THE UPPER
RIDGE RETREATS WEST.  ELSEWHERE OVER THE CARIBBEAN...LOWER LEVEL
MOISTURE APPEARS TO BE SOMEWHAT LIMITED WITH AN UNUSUAL ABSENCE
OF SHOWERS.

SUBTROPICAL ATLANTIC OCEAN...
SHOWERS/THUNDERSTORMS CONTINUE ALONG OVER THE FAR W ATLC IN
ASSOCIATION WITH A SHORTWAVE TROUGH OVER THE SE UNITED STATES.
THE CONVECTION IS PRIMARILY FOCUSED ALONG THE GULF STREAM FROM
CENTRAL FLORIDA NWD TO THE CAROLINAS. ELSEWHERE OVER THE W ATLC
...A MID-UPPER LEVEL RIDGE EXTENDS E/W ALONG 28N/29N WEST OF
55W. THE RIDGE IS BEING SHUNTED SWD BY A DIGGING TROUGH N OF THE
AREA WITH ATTENDANT SURFACE FRONTAL BOUNDARY JUST N OF THE AREA
ALONG 32N.  GOOD UPPER LEVEL DYNAMICS AHEAD OF THE AMPLIFYING
TROUGH COUPLED WITH LOW LEVEL MOISTURE POOLING AHEAD OF THE
SURFACE FRONT IS PRODUCING AN AREA OF SCATTERED SHOWERS AND
THUNDERSTORMS N OF 27N BETWEEN 60W-67W.  SOUTH OF THE W ATLC
RIDGE AXIS...THE FLOW BECOMES CONFLUENT PRODUCING SUBSIDENCE AND
DRY AIR ACROSS MUCH OF THE BAHAMAS MOVING WESTWARD OVER S
FLORIDA.  OVER THE CENTRAL ATLC...MID-OCEANIC TROUGH EXTENDS
FROM 30N53W SWD OVER W HISPANIOLA.  THERE IS JUST ENOUGH
INSTABILITY ASSOCIATED WITH AN UPPER LOW NEAR 29N54W TO SUPPORT
A SMALL AREA OF SCATTERED SHOWERS/ISOLATED THUNDERSTORMS FROM
25N-30N BETWEEN 50W-55W.  E OF THE MID-OCEANIC
TROUGH...SUBSIDENCE AND DRY AIR AT ALL LEVELS PREVAILS LIMITING
SIGNIFICANT CLOUDS/CONVECTION. AT THE SURFACE...A BREAK IN THE
SUBTROPICAL RIDGE EXISTS OVER THE W ATLC IN ASSOCIATION WITH A
FRONTAL ZONE ALONG 32N W OF 60W. OVER THE E ATLC...RIDGE EXTENDS
FROM THE AZORES SW TO 26N45W.

TROPICAL ATLANTIC...
MID-UPPER LEVEL RIDGE EXTENDS FROM W AFRICA NEAR MAURITANIA WSW
ALONG 17N30W TO 16N50W.  A BREAK IN THE UPPER RIDGE IS PRESENT W
OF 50W IN ASSOCIATION WITH A WEAK TROUGH ALONG 17N50W TO 10N55W.
STRONG SUBSIDENCE W OF THE UPPER TROUGH BLANKETS THE AREA WEST
OF T.S. FRANCES.   HOWEVER...THIS AIR APPEARS TO BE HAVING
LITTLE OR NO AFFECT ON FRANCES WHICH IS STRENGTHENING.
RATHER...FRANCES CONTINUES TO BENEFIT FROM THE LOW SHEAR
ENVIRONMENT WHICH EXTENDS ACROSS A GOOD PORTION OF THE TROPICAL
ATLC.  AT THE LOWER LEVELS...MONSOON FLOW CONTINUES TO EXTEND AS
FAR WEST AT 40W.

$$
RHOME




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