[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 261101
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM 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 0600 UTC SURFACE ANALYSIS AND
SATELLITE IMAGERY THROUGH 1045 UTC.

...SPECIAL FEATURE...
TROPICAL STORM FRANCES CENTER NEAR 12.6N 43.7W...OR ABOUT
1195 MILES...1925 KM...EAST OF THE LESSER ANTILLES...
AT 26/0900 UTC. FRANCES IS MOVING WEST-NORTHWEST 15 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE 996 MB. MAXIMUM SUSTAINED
WIND SPEED 50 KT GUSTS 60 KT. SEE THE LATEST NHC FORECAST/
ADVISORY ISSUED UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC
FOR MORE DETAILS. THE CLOUD PATTERN OF FRANCES IS BETTER
ORGANIZED WITH A WELL-DEFINED CURVED CLOUD BAND...DEEP
CONVECTION NEAR THE CENTER AND GOOD UPPER LEVEL OUTFLOW.
THERE WERE SOME EARLIER INDICATIONS THAT AN EYE WAS TRYING TO
FORM. THE WIND SPEED MIGHT BE ACTUALLY FASTER IF AN EYE FORMS...
THE SHEAR IS LOW AND THE OCEAN IS WARM...AND STRENGTHENING IS
INDICATED. GLOBAL MODELS CONTINUE TO FORECAST A MID-LEVEL TROUGH
OVER THE CENTRAL ATLANTIC. IT IS LIKELY THAT THE TROUGH WILL
ERODE THE SUBTROPICAL RIDGE IN THE SHORT TERM...FORCING FRANCES
TO MOVE TOWARD THE WEST-NORTHWEST AND NORTHWEST WITH A DECREASE
IN FORWARD SPEED. THEREAFTER...ONCE THE TROUGH MOVES OUT OR
WEAKENS...MODELS ARE UNANIMOUSLY REDEVELOPING THE SUBTROPICAL
RIDGE TO THE NORTH OF FRANCES. IT IS LIKELY THAT THIS WILL RESULT
ON A TRACK BACK TO WEST-NORTHWEST OR EVEN TOWARD THE WEST
DEPENDING OF THE INTENSITY OF THE RIDGE. SCATTERED STRONG SHOWERS
AND THUNDERSTORMS FROM 15N41W TO 11N46W TO 15N46W TO 15N41W.

...TROPICAL WAVES...
TROPICAL WAVE ALONG 17W/18W SOUTH OF 22N MOVING WEST 10-15 KT.
BROAD TROUGH IN THE SURFACE OBSERVATIONS OF WEST AFRICA.
COMPARATIVELY STRONGER SHOWERS AND THUNDERSTORMS IN SOUTHWESTERN
MAURITANIA THAN THAT IN NORTHWESTERN SENEGAL. ISOLATED MODERATE
TO LOCALLY STRONG SHOWERS AND THUNDERSTORMS IN THE ITCZ FROM 5N
TO 13N BETWEEN 18W AND 28W.

TROPICAL WAVE ALONG 65W/66W SOUTH OF 16N MOVING WEST 20 KT.
THIS WAVE IS WEAK...AND DIFFICULT TO IDENTIFY IN SATELLITE
IMAGERY 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 THAT A MID-LEVEL
WIND SHIFT IN THE ISLANDS TOMORROW ASSOCIATED WITH A SURGE IN
THE TRADES CURRENTLY ALONG 53W AND PERHAPS THIS...ARE ASSOCIATED
WITH THE WAVE.

...ITCZ...
ITCZ 8N13W 8N30W 10N37W 7N42W 5N50W 9N62W. ITCZ PRECIPITATION
JUST WEST-SOUTHWEST OF THE 17W/18W TROPICAL WAVE. ISOLATED
MODERATE SHOWERS AND THUNDERSTORMS WITHIN 30 TO 60 NM ON EITHER
SIDE OF AXIS BETWEEN 48W AND 56W.

...DISCUSSION...
THE GULF OF MEXICO...
INVERTED MIDDLE TO UPPER LEVEL TROUGH FROM CENTRAL FLORIDA TO
A YUCATAN PENINSULA MIDDLE TO UPPER LEVEL CYCLONIC CIRCULATION
CENTER. WIDELY SCATTERED MODERATE TO ISOLATED STRONG SHOWERS
AND THUNDERSTORMS ALONG THE FLORIDA WEST COAST FROM 25N TO 27N
EAST OF 84W. ISOLATED MODERATE SHOWERS AND THUNDERSTORMS
ELSEWHERE SOUTHEAST OF 30N89W 25N91W 21N92W. UPPER LEVEL
NORTHEASTERLY WIND FLOW EVERYWHERE WEST OF THE INVERTED TROUGH.

THE CARIBBEAN SEA...
UPPER LEVEL MOISTURE COVERS THE CARIBBEAN SEA SOUTH OF 19N.
STRONG SHOWERS AND THUNDERSTORMS IN INDIVIDUAL CLUSTERS ARE
SOUTHWEST OF 16N81W 12N80W 11N75W...UNDER AN UPPER LEVEL RIDGE
AND SOME ITCZ INFLUENCE. UPPER LEVEL SOUTHWESTERLY WIND FLOW
EVERYWHERE EAST OF 70W.

SUBTROPICAL ATLANTIC OCEAN...
UPPER LEVEL RIDGE ALONG 29N WEST OF 60W. COLD/STATIONARY FRONT
ALONG 32N BETWEEN 60W AND THE GEORGIA COASTAL WATERS...LEADING
TO A SURFACE TROUGH FROM 31N80W TO 28N83W AT THE FLORIDA WEST
COAST...TO 24N85W IN THE SOUTHEASTERN GULF OF MEXICO. ISOLATED
TO WIDELY SCATTERED MODERATE/LOCALLY STRONG SHOWERS AND
THUNDERSTORMS NORTH OF 28N BETWEEN 60W AND 80W UNDER THE UPPER
LEVEL RIDGE AND SOME UPPER LEVEL DIFFLUENT FLOW.  UPPER LEVEL
ANTICYCLONIC FLOW EVERYWHERE NORTH OF 20N WEST OF 60W. SURFACE
TROUGH ALONG 54W FROM 22N TO 29N. WIDELY SCATTERED TO SCATTERED
MODERATE/ISOLATED STRONG SHOWERS AND THUNDERSTORMS FROM 25N TO
30N BETWEEN 50W AND 54W.

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.

$$
MT



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