[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 252336
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT WED 25 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURE...
TROPICAL DEPRESSION SIX HAS BEEN UPGRADED TO TROPICAL STORM
FRANCES CENTERED NEAR 11.6N 40.5W AT 25/2100 UTC MOVING W 15 KT.
MAXIMUM SUSTAINED WINDS ARE 35 KT GUSTS 45 KT. THE ESTIMATED
MINIMUM CENTRAL PRESSURE IS 1005 MB. SEE THE LATEST NHC
FORECAST/ADVISORY ISSUED UNDER AWIPS/WMO HEADERS MIATCMAT1/
WTNT21 KNHC FOR MORE DETAILS.  FRANCES IS ON A DEVELOPING TREND
WITH A LARGE SPIRAL BAND CURVING NW TO W THEN SW OF THE STORM
AND A FEW TSTMS NEAR THE CENTER.  ENVIRONMENTAL CONDITIONS LOOK
FAVORABLE FOR MORE INTENSIFICATION AS AN UPPER ANTICYCLONE IS
NEAR THE STORM CAUSING LITTLE SHEAR AND BUOYS IN THE PROJECTED
PATH HAVE SEA-SURFACE TEMPERATURES OF 82-83F.   WIDELY SCATTERED
TO SCATTERED MODERATE FROM 10N-14N BETWEEN 40W-43W.

...TROPICAL WAVES...
TROPICAL WAVE IS ALONG 17W S OF 22N MOVING W AT 10-15 KT.  BROAD
TROUGHING IS SEEN IN THE SURFACE OBSERVATIONS OVER W AFRICA.
MOST OF THE CONVECTION WITH THE WAVE IS STILL OVER LAND BUT
ISOLATED MODERATE IS PRESENT BETWEEN 7N-12N BETWEEN 13W-22W.
THE 00Z RAOB FROM DAKAR WILL BE USED TO FURTHER REFINE THE
WAVE'S POSITION.

TROPICAL WAVE IS ALONG 61W S OF 16N MOVING W AT 20 KT. THIS WAVE
IS VERY WEAK WITH LITTLE SIGNATURE SEEN IN SATELLITE PICTURES OR
UPPER-AIR DATA.  LONG-TERM SATELLITE LOOPS SUGGEST THAT THE WAVE
HAS BEEN WEAKENING DURING ITS TREK ACROSS THE ATLC WITH NO
OBVIOUS POSITION.  THE GFS INDICATES A MID-LEVEL WIND SHIFT IN
THE ISLANDS TOMORROW ASSOCIATED WITH A SURGE IN THE TRADES
CURRENTLY ALONG 53W AND PERHAPS THIS IS ASSOCIATED WITH THE
WAVE.  IN ANY EVENT LITTLE WEATHER IS EITHER LOCATION TONIGHT.

...ITCZ...
ITCZ IS CENTERED ALONG 10N18W 7N25W 9N36W 5N47W 9N60W.  ITCZ IS
NOT WELL-DEFINED W OF 45W.  WIDELY SCATTERED MODERATE WITHIN
30/45 NM OF AXIS BETWEEN 56W-60W.  ISOLATED MODERATE WITHIN 60
NM OF AXIS BETWEEN 45W-52W AND FROM 6N-10N BETWEEN 18W-25W.

...DISCUSSION...
GULF OF MEXICO...
THE GULF IS SPLIT INTO TWO WEATHER SITUATIONS TODAY WITH HIGH
PRESSURE OVER THE W & CENTRAL GULF WHILE A SURFACE TROUGH
LINGERING OVER NE FLORIDA INTO NW CUBA.  THE WEATHER IS MOSTLY
DRY W OF 90W OVER THE GULF WATERS COURTESY OF A MID/UPPER HIGH
NEAR CORPUS CHRISTI RIDGING EASTWARD TO 89W.  A DIFFERENT STORY
IN THE E GULF WITH STRONG TSTMS DROPPING HEAVY RAIN OVER CENTRAL
FLORIDA WITH DEEP-LAYERED TROUGHING FROM JACKSONVILLE TO THE DRY
TORTUGAS.   LITTLE CHANGE IS LIKELY WITH THE PATTERN NEARLY
STATIONARY... ENHANCING RAIN CHANCES OVER THE CENTRAL/SOUTHERN
PART OF FLORIDA.

CARIBBEAN SEA...
TWO MID/UPPER LOWS ARE THE DOMINANT FEATURES IN BROAD TROUGHING
OVER THE CARIBBEAN... ONE NEAR 17N74W S OF HAITI WHILE ANOTHER
IS IN THE GULF OF HONDURAS.  ELY FLOW N OF 20N IS MOVING CIRRUS
DEBRIS FROM CUBA OVER THE NW CARIBBEAN WITH OTHER ISOLATED
SHOWERS N OF 15N OF 83W ENHANCED BY THE WESTERNMOST UPPER LOW.
THE MUCH LARGER FEATURE IS S OF CUBA WITH 40 KT UPPER WLY FLOW S
OF THE TROUGH.  SOME DIFFLUENCE ALONG WITH THE NEARBY ITCZ IS
CAUSING ISOLATED TSTMS S OF 12N BETWEEN 75W-81W.  DRY MID/UPPER
LEVEL AIR IS MOVING INTO THE E CARIBBEAN...SQUELCHING ANY
SIGNIFICANT CONVECTION.  THE UPPER PATTERN IS ALSO FAIRLY
STATIONARY OVER THE CARIBBEAN WITH LITTLE CHANGE LIKELY UNTIL
THE ATLC RIDGE IS FORECAST TO BUILD BACK INTO THE NE CARIBBEAN
FOR THE WEEKEND.

SUBTROPICAL ATLANTIC OCEAN...
THE N AND W PORTION OF THE AREA IS SOMEWHAT UNSETTLED WHILE THE
ATLC E OF 45W IS CONVECTION-FREE.  MID/UPPER HIGH NEAR 30N76W
RIDGING ENE TO 32N60W IS PROVIDING A FAVORABLE ENVIRONMENT FOR
ISOLATED MODERATE N OF 28N..MOSTLY S OF A STATIONARY FRONT
LOCATED ALONG 32N BETWEEN BERMUDA AND 80W.  MID-OCEANIC TROUGH
ENTERS THE AREA NEAR 32N55W SW INTO AN UPPER LOW NEAR 29N57W
CONTINUING SW INTO HISPANIOLA.  ISOLATED SHOWERS ARE N OF 26N
BETWEEN 55W-60W IN THE MORE UNSTABLE AIR ALOFT NEAR THE TROUGH
AXIS.  DIFFLUENCE E OF THE UPPER TROUGH ALONG WITH A WEAK
LOW-LEVEL TROUGH ALONG 51W IS CAUSING WIDELY SCATTERED WEAK/
MODERATE CONVECTION FROM 25N-31N BETWEEN 50W-53W.  FOR THE REST
OF THE CENTRAL/E ATLC... UPPER HIGH IS NEAR 24N47W... AND AN
UPPER TROUGH IS NEAR 31N22W TO 21N34W.  NO SIGNIFICANT WEATHER
WITH VERY DRY MID/UPPER LEVEL AIR PRESENT.

TROPICAL ATLANTIC...
MID-UPPER HIGH IS ALONG 19N16W IN NW MAURITANIA WSW ACROSS THE
NW CAPE VERDES TO 16N40W THEN 16N50W.  A BREAK IN THE UPPER
RIDGE IS PRESENT W OF 50W THOUGH THE MID-LEVEL RIDGE EXTENDS
FROM THE SUBTROPICS NEAR 20N48W TO 15N57W.  STRONG SUBSIDENCE W
OF 45W AND E OF 35W IS PRESENT... FRANCES APPEARS TO BE IN A
RATHER SMALL AREA OF UPPER MOISTURE.  WHETHER THIS HAS AN EFFECT
OF THE STORM REMAINS TO BE SEEN.  DIVERGENCE IS PRESENT NEAR AND
W OF THE CYCLONE.. FUELING THE TSTMS.  MODELS BUILD THE UPPER
RIDGE WESTWARD WITH TIME... KEEPING LOW SHEAR ACROSS FRANCES FOR
AT LEAST THE NEXT COUPLE OF DAYS.  LOW-LEVEL WLY MONSOON FLOW
NOW EXTENDS ALL THE WAY TO 45W ALONG 8N-10N.. MUCH FARTHER W
THAN AVERAGE.

$$
BLAKE

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