[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 031758
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT FRI 03 SEP 2004

TROPICAL WEATHER DISCUSSION FOR N AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN  SECTIONS
OF S AMERICA...AND ATLC 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
1715 UTC.

...SPECIAL FEATURES...

HURRICANE FRANCES AT 2PM EDT/1800 UTC...WAS NEAR LATITUDE 25.7N
...LONGITUDE 77.2 W NEAR THE SOUTHERN TIP OF GREAT ABACO ISLAND
IN THE BAHAMAS. THIS POSITION ALSO IS ABOUT 200 MILES E-SE OF
THE FLORIDA LOWER E COAST. MAXIMUM SUSTAINED WIND SPEED 115 MPH/
185 KM/HR WITH HIGHER GUSTS. THE LATEST MINIMUM CENTRAL PRESSURE
MEASURED WAS 961 MB. SEE LATEST NHC PUBLIC ADVISORY UNDER
AWIPS/WMO HEADERS MIATCPAT1/ WTNT31 KNHC AND THE
FORECAST/ADVISORY UNDER HEADERS MIATCMAT1/WTNT21 KNHC FOR
ADDITIONAL INFORMATION. NUMEROUS STRONG SHOWERS AND TSTMS
SURROUND THE CENTER FROM 23N-28N BETWEEN 74W-78W. THE OUTERMOST
RAIN BANDS HAVE BEEN MOVING ACROSS THE FLORIDA E COAST S OF FORT
PIERCE AND THROUGH THE STRAITS OF FLORIDA....WITH THE HEAVIEST
BANDS MOVING SE ACROSS THE CAY SAL BANK AND ONTO THE N COAST OF
CUBA. UPPER OUTFLOW EXTENDS N AS FAR AS 34N AND AS FAR E AS 63W.
OUTFLOW OVER THE W SEMICIRCLE IS RESTRICTED BY UPPER LEVEL
SHEARING AND POSSIBLY SOME DRIER AIR IS INTRUDING INTO W AND S
QUADRANTS...ALL AIDING IN A WEAKENING STAGE.

TROPICAL STORM IVAN IS CENTERED NEAR 32.9N 32.9W AT 03/1500
UTC...AND IS EMBEDDED IN DEEP ELY FLOW WHICH IS MOVING IVAN W AT
260 DEG AT 16 KT. THE MAXIMUM SUSTAINED WIND SPEED IS 40 KT WITH
GUSTS TO 50 KT...AND BASED ON LATEST QSCAT WINDS THIS COULD
CONSERVATIVE. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1003 MB. SEE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS. NUMEROUS STRONG SHOWERS
AND TSTMS EXIST FROM 7N-12.5N BETWEEN 31W-36W. THIS MORNINGS
SATELLITE CLASSIFICATION MEASURED 7/10 BANDING OVER W SEMICIRCLE
WITH SLIGHT NE SHEAR INDICATED. AN UPPER ANTICYCLONE IS CENTERED
NEAR 15N35W WITH A RIDGE EXTENDING W-SW TO A CREST AT 10N47W.
THUS UPPER LEVEL CONDITIONS WILL REMAIN FAVORABLE FOR CONTINUED
STRENGTHENING OF IVAN TO HURRICANE STATUS IN ABOUT 48 HOURS.

...TROPICAL WAVES...

LOW PRES...ABOUT 1013 MB...CONTINUES NEAR 21.5N44W...ORIGINALLY
SPAWNED ALONG THE NORTHERN EXTENSION OF A HIGH LATITUDE TROPICAL
WAVE THAT IS CURRENTLY DIFFICULT TO LOCATE OR IDENTIFY...EVEN
WITH HIGH RESOLUTION VISIBLE IMAGERY. THUS I DROPPED THE WAVE
FROM THE SURFACE ANALYSIS AT 1200 UTC. THE LOW LEVEL SYSTEM IS
MOVING W UNDER A TROPICAL UPPER TROUGH...TUTT...RESULTING IN A
CONVECTIVE BLOWUP SITUATION. THE CONVECTION IS SHEARED TO THE NE
OF AN EXPOSED LOW LEVEL CIRCULATION CENTER AT THE MOMENT. SINCE
THE UPPER LEVEL DIFFLUENCE IS EXPECTED TO CONTINUE TO FLARE
CONVECTION SATELLITE CLASSIFICATIONS HAVE RESUMED...BUT JUST
BELOW DEPRESSION STATUS. MODELS ARE HAVING A DIFFICULT TIME WITH
THIS LOW BUT MOVE IT N TO NEAR 30N44W IN 24 HOURS AND WEAKENING
THE LOW. THIS MAY BE IN RESPONSE TO A BAROCLINIC BOUNDARY N OF
THE FORECAST AREA. IN ANY EVENT THE AREA WILL BE MONITORED
CLOSELY.

THE TROPICAL WAVE ALONG 65W S OF 22N IS MOVING W ABOUT 12 KT.
THE WAVE AXIS IS DIFFICULT TO ACCURATELY LOCATE AS BROAD
CYCLONIC TURNING IS INDICATED IN THE TRADE WIND CUMULUS MOVING W
THROUGH THE E CARIBBEAN WATERS. THE WAVE AXIS WAS HELD BACK TO
THE E A TAD THIS MORNING BASED ON CYCLONIC TURNING OVER INTERIOR
VENEZUELA...ALONG 66W AT THE MOMENT.

...ITCZ...

ITCZ AXIS 7N7E 5N1W 6N25W 8N32W 5N37W 10N63W. WIDELY SCATTERED
MODERATE AND ISOLATED STRONG CONVECTION OBSERVED WITHIN 90 NM OF
7N17W. ONLY ISOLATED MODERATE NOTED WITHIN 180 NM OF AXIS
BETWEEN 35W-46W.

...DISCUSSION...

GULF OF MEXICO...
A MID TO UPPER LAYER TROUGH EXTENDS S INTO THE GULF ALONG
31N90W 26N92W THROUGH THE BAY OF CAMPECHE TO A SMALL UPPER
CYCLONE JUST S OF THE GULF OF TEHUANTEPEC AT 14N95W...WITH THE
TROUGH CONTINUING SW INTO THE TROPICAL E-PAC TO A BASE NEAR
7N98W. THE TROUGH IS SHIFTING W OVER THE GULF OF MEXICO S OF 26N
AND QUASI-STATIONARY N OF 25N. AT THE LOW LEVELS...A BROAD
TROUGH IS ANALYZED ALONG THE TEXAS COASTAL PLAINS. ASSOCIATED
UPPER SUBSIDENCE IS NOTED WITHIN 90 NM EITHER SIDE OF THE UPPER
TROUGH AXIS...AND IS SUPPRESSING CONVECTION TO ISOLATED
MODERATE...ROUGHLY WITHIN 90 NM OF ITS AXIS.

TO THE E OF THIS UPPER TROUGH...AN UPPER ANTICYCLONE...
CONTRIBUTING TO THE STEERING OF HURRICANE FRANCES...HAS SHIFTED
NE TO NEAR 32N81W BASED ON CLOUD MOTION WINDS. A RIDGE EXTENDS
SW ACROSS N FLORIDA TO 28N87W. THE SMALL UPPER CYCLONE THAT WAS
CENTERED NEAR 22N85W IS LOSING IDENTITY IN THE BROAD UPPER
CYCLONIC FLOW OBSERVED OVER THE GULF S OF 25N BETWEEN 85W-89W.
ELSEWHERE E OF THE TROUGH...A FEW SHOWERS AND TSTMS CONTINUE TO
FLARE NEAR 29N87W AND ARE MOVING ANTICYCLONICALLY NE THROUGH THE
MID-LEVEL STEERING RIDGE. BROAD UPPER SUBSIDENCE COVERS FLORIDA
BETWEEN 85W-81W...BUT IS ERODING ALONG THE EASTERN EDGE WITH THE
APPROACH OF THE MOISTURE PLUME ASSOCIATED WITH HURRICANE
FRANCES.

TO THE W OF THE TROUGH...AN UPPER ANTICYCLONE IS FORMING NEAR
26N95W ALONG THE UPPER RIDGE FORMALLY ASSOCIATED WITH HURRICANE
HOWARD IN THE E-PAC. ASSOCIATED UPPER DIFFLUENCE IS ENHANCING
CONVECTION ALONG THE TEXAS COASTAL TROUGH...WITH THE DEBRIS
MOISTURE ADVECTED NE ACROSS THE MISSISSIPPI VALLEY AND
EVENTUALLY ACROSS THE NE CONUS. THE RIDGE FROM HOWARD IS STILL
EXTENDING NE ACROSS OLD MEXICO ALONG 20N108W TO A CREST NEAR
23N98W. THE MOISTURE PLUME FROM HOWARD'S CONVECTION IS FOR THE
MOST PART NOW REMAINING W OF THE AREA OVER INTERIOR OLD MEXICO.

CARIBBEAN...
A SMALL UPPER ANTICYCLONE CONTINUES SW OF HURRICANE FRANCES NEAR
21.5N81W...AND IS CONTRIBUTING TO THE WLY SHEAR THAT FRANCES IS
EXPERIENCING. THE BROAD UPPER CYCLONIC TURNING OVER THE YUCATAN
CHANNEL AND S-CENTRAL GULF OF MEXICO IS ACCOMPANIED BY STRONG
UPPER LEVEL SUBSIDENCE...AND CONVECTION IS SUPPRESSED TO A FEW
SHOWERS. THIS SUPPRESSION WILL CONTINUE TO PROVIDE BEAUTIFUL
SAILING WEATHER IN THE NW CARIBBEAN WHERE MANY CRUISE SHIPS AND
RECREATIONAL CRAFT ARE HOLDING UP WAITING FOR HURRICANE FRANCES
TO MOVE N...ALLOWING PORT ENTRY TO RESUME IN SOUTHERN FLORIDA.

UPPER DEBRIS MOISTURE FROM EARLIER CONVECTION OVER VENEZUELA IS
SPREADING NE ACROSS THE SE CARIBBEAN SEA INTO AN UPPER LOW NEAR
16N60W. UPPER DEBRIS MOISTURE ACCOMPANIED BAY A FEW SHOWERS AND
TSTMS...ARE SPREADING SW INTO THE NE CARIBBEAN...ASSOCIATED WITH
THIS SAME UPPER CYCLONE AT 16N60W...WHICH IS SHIFTING W WITH
TIME.

ELSEWHERE...THE UPPER LEVELS OF THE CARIBBEAN ARE DOMINATED BY
THE UPPER ANTICYCLONIC FLOW FROM HURRICANE FRANCES...WITH STRONG
UPPER SUBSIDENCE SUPPRESSING CONVECTION. THINNING DEBRIS
MOISTURE FROM HURRICANE FRANCES IS STILL SPREADING SW OVER THE
REGION N OF 16N BETWEEN 69W-80W.

REMAINDER OF SUBTROPICAL ATLC...
AN UPPER LEVEL TROUGH LIES NEARLY STATIONARY FROM 32N7W TO AN
UPPER CYCLONE DEVELOPING AT 23N23W...WITH A CYCLONIC SHEAR AXIS
THEN EXTENDING NW TO ANOTHER UPPER CYCLONE WHICH LIES NEAR
33N30W. THIS TROUGH AND SHEAR AXIS ARE IDENTIFIED BY MODERATE TO
STRONG UPPER SUBSIDENCE WITHIN 75 NM EITHER SIDE OF THEIR AXIS.
AN UPPER ANTICYCLONE IS NOTED AT 23N36W WITH A RIDGE AMPLIFYING
N ALONG 40W TO A SHARP CREST AT 36N40W. ASSOCIATED UPPER
DIFFLUENCE IS ENHANCING SCATTERED CONVECTION NE OF THE SURFACE
LOW NEAR 21N44W. AN UPPER CYCLONE IS POSITIONED JUST TO THE W OF
THE RIDGE NEAR 31N46W WITH A TROUGH SW ALONG 28N49W TO AN UPPER
CYCLONE NEAR 16N60W.  DEEP UPPER MOISTURE IS NOTED OVER THE ATLC
WITHIN 300 NM EITHER SIDE OF LINE 32N38W 15N60W.

TROPICAL ATLC...
UPPER DIFFLUENCE IS ENHANCING SCATTERED SHOWERS AND TSTMS FROM
11N-19N BETWEEN 61W-51W. A SQUALL LINE HAS MOVED OFF THE
AFRICAN COAST WITH SCATTERED MODERATE TO STRONG CONVECTION FROM
8N1-17N E OF 20W.

$$
NELSON




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