[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 040014
TWDAT

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

...SPECIAL FEATURES...

HURRICANE FRANCES IS CENTERED NEAR 25.9N 77.5 W AT 2100 UTC
MOVING WEST NORTHWEST AT 7 KT.  MAXIMUM SUSTAINED WIND SPEED IS
100 KT WITH GUSTS TO 120 KT.  MINIMUM CENTRAL PRESSURE IS 959
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.  FRANCES HAS
WEAKENED SLIGHTLY IN THE PAST SIX HOURS WITH LESS CONVECTION IN
FEEDER BANDS.  THE WIND FIELD HAS BROADENED OVER A GREATER AREA.
FRANCES REMAINS A DANGEROUS HURRICANE.  OUTFLOW IS MOST
PRONOUNCED IN THE EAST SEMICIRCLE DUE TO SOME WESTERLY SHEAR
ALOFT.  DRY SUBSIDENCE IS ALSO NOTED ON WATER VAPOR IMAGERY W OF
THE CENTER OVER FLORIDA AND THE EASTERN GULF OF MEXICO.
NUMEROUS STRONG CONVECTION IS NEAR THE CENTER FROM 25N-27N
BETWEEN 76W-78W.  SCATTERED MODERATE CONVECTION EXTENDS FROM
24N-28N BETWEEN 74W-78W.

TROPICAL STORM IVAN IS CENTERED NEAR 8.9N 34.6W AT 03/2100
UTC...AND IS EMBEDDED IN DEEP ELY FLOW WHICH IS MOVING IVAN W AT
255 DEG AT 17 KT. THE MAXIMUM SUSTAINED WIND SPEED IS 45 KT WITH
GUSTS TO 55 KT...AND BASED ON LATEST QSCAT WINDS THIS COULD
CONSERVATIVE. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1000 MB. SEE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS.  UPPER LEVEL CONDITIONS
WILL REMAIN FAVORABLE FOR CONTINUED STRENGTHENING OF IVAN TO
HURRICANE STATUS IN 48 HOURS.  NUMEROUS STRONG CONVECTION IS
FROM 7N-10N BETWEEN 33W-36W.  SCATTERED MODERATE TO STRONG
CONVECTION IS FROM 5N-10N BETWEEN 33W-39W.

...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 66W/67W S OF 22N IS MOVING W ABOUT 12
KT. THE WAVE AXIS IS DIFFICULT TO LOCATE AS BROAD CYCLONIC
TURNING IS INDICATED IN THE TRADE WIND CUMULUS MOVING W THROUGH
THE E CARIBBEAN WATERS. NO SIGNIFICANT CONVECTION IS NOTED.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 9N10W 11N25W 7N40W 11N57W 12N70W
8N80W. WIDELY SCATTERED MODERATE AND ISOLATED STRONG CONVECTION
IS OBSERVED OVER N COLOMBIA AND PANAMA FROM 7N-11N BETWEEN
74W-83W.

...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 16N96W...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.  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.  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.

CARIBBEAN...
A SMALL UPPER ANTICYCLONE CONTINUES SW OF HURRICANE FRANCES NEAR
22N82W...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.

$$
FORMOSA


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