[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 260605
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 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 0000 UTC SURFACE ANALYSIS AND
SATELLITE IMAGERY THROUGH 0515 UTC.

...SPECIAL FEATURE...
TROPICAL STORM FRANCES CENTER NEAR 11.8N 41.7W...OR ABOUT
1340 MILES/2155 KM EAST OF THE LESSER ANTILLES...AT 26/0300 UTC.
FRANCES IS MOVING WEST 14 KT. ESTIMATED MINIMUM CENTRAL PRESSURE
1005 MB. MAXIMUM SUSTAINED WIND SPEED 35 KT GUSTS 45 KT.
SEE THE LATEST NHC FORECAST/ADVISORY ISSUED UNDER AWIPS/WMO
HEADERS MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS. UPPER-LEVEL
OUTFLOW IS WELL-DEFINED EXCEPT TO THE EAST AND VERTICAL SHEAR
SHOULD REMAIN LOW ALONG THE PATH OF THE TROPICAL CYCLONE FOR
THE NEXT 2 TO 3 DAYS. INTENSIFICATION IS LIKELY IN SPITE OF
THE RECENT LEVELLING OFF IN THE DEVELOPMENT OF THIS CYCLONE.
THE UPPER-LEVEL WINDS MAY BECOME LESS FAVORABLE AS INCREASING
WESTERLY SHEAR IS INDICATED IN MODELS FOR 72 AND 96 HOURS.
A MIDDLE LATITUDE 500 MB TROUGH IS FORECAST TO DROP INTO THE
CENTRAL ATLANTIC DURING THE NEXT COUPLE OF DAYS. THIS FEATURE
IS CERTAINLY AT TOO HIGH A LATITUDE TO IMPACT DIRECTLY THE
STEERING OF FRANCES. MODELS FORECAST THE TROUGH TO WEAKEN THE
SUBTROPICAL RIDGE TO THE NORTH OF FRANCES WHICH SHOULD CAUSE A
FURTHER SLOWING OF THE FORWARD SPEED AND A GRADUAL TURN TO THE
RIGHT. SCATTERED STRONG SHOWERS AND THUNDERSTORMS FROM 11N TO
14N BETWEEN 41W AND 44W.

...TROPICAL WAVES...
TROPICAL WAVE ALONG 17W 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 11N BETWEEN 16W AND 28W.

TROPICAL WAVE ALONG 63W/64W 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. IS CENTERED ALONG
10N18W 7N25W 9N36W 5N47W 9N60W. ISOLATED MODERATE SHOWERS AND
THUNDERSTORMS IN A FEW SMALL CLUSTERS...FROM 9N TO 10N BETWEEN
52W AND 54W...AND FROM 8N TO 9N BETWEEN 59W AND 62W. WARMING
CLOUD TOP TEMPERATURES IN AN OUTER BAND OF EARLIER RAIN...IS
FROM 4N TO 6N BETWEEN 47W AND 50W.

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...
THE GULF OF MEXICO...
SURFACE RIDGE FROM THE FLORIDA PANHANDLE TO THE CENTRAL GULF...
AND EVENTUALLY THE SOUTHWESTERN CORNER OF THE AREA. SURFACE
TROUGH 31N17W...ACROSS CENTRAL FLORIDA...TO THE WESTERN TIP OF
CUBA. THIS SURFACE TROUGH COINCIDES WITH A MIDDLE TO UPPER LEVEL
TROUGH...FROM JUST SOUTHEAST OF THE FLORIDA BIG BEND...TO THE
NORTHERN YUCATAN PENINSULA TO THE MEXICO/SOUTHWESTERN GUATEMALA
BORDER. ISOLATED MODERATE SHOWERS SOUTHEAST OF 30N86W 19N94W.
MIDDLE TO UPPER LEVEL DRY AIR WEST OF 94W.

THE CARIBBEAN SEA...
UPPER LEVEL MOISTURE COVERS THE CARIBBEAN SEA SOUTH OF 20N68W
16N78W16N74W. ISOLATED MODERATE SHOWERS AND THUNDERSTORMS
ARE UNDER THIS UMBRELLA. TWO MID/UPPER LOWS ARE THE DOMINANT
FEATURES IN A BROAD TROUGH IN THE CARIBBEAN...ONE IS BETWEEN
JAMAICA AND CUBA. SHOWERS AND THUNDERSTORMS IN NORTHWESTERN
HAITI WITH SOME UPPER LEVEL DIFFLUENT FLOW.

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. SCATTERED MODERATE TO ISOLATED STRONG SHOWERS AND
THUNDERSTORMS FROM 26N TO 29N BETWEEN 50W AND 53W. DIFFLUENCE
EAST OF THE UPPER TROUGH ALONG WITH A WEAK LOW-LEVEL TROUGH
ALONG 52W/53W 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.

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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