[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 131755
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT MON 13 SEP 2004

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN
SECTIONS OF SOUTH 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 FEATURE...
HURRICANE IVAN IS CENTERED NEAR 20.9N 84.7W OR 70 MILES SSE OF
THE W TIP OF CUBA AT 13/1800 UTC MOVING WNW AT 7 KT. MAXIMUM
SUSTAINED WIND SPEED HAS INCREASED TO 140 KT WITH HIGHER GUSTS
MAKING IVAN A DANGEROUS CATEGORY 5 HURRICANE ON THE
SAFFIR-SIMPSON SCALE. MINIMUM CENTRAL PRESSURE HAS FALLEN TO 914
MB. SEE LATEST NHC PUBLIC ADVISORY OR NHC FORECAST/ADVISORY
UNDER AWIPS/WMO HEADERS MIATCPAT4/WTNT34 KNHC OR
MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS.
IVAN IS SOMEWHAT LESS SYMMETRIC IN SATELLITE IMAGERY TODAY WITH
INTENSE CONVECTION ONLY WITHIN 60 NM OVER THE NW SEMICIRCLE AND
WITHIN 150 NM OVER THE SE SEMICIRCLE. HOWEVER...THE 30 NM WIDE
EYE REMAINS DISTINCT AND CLOUD TOP TEMPERATURES HAVE COOLED INTO
THE -70 TO -80 DEGREE CELSIUS RANGE.  OUTER RAINBANDS EXTEND NWD
OVER THE W HALF OF CUBA INTO THE FLORIDA STRAITS TO THE FLORIDA
KEYS. RAINBANDS ALSO EXTEND SWD TO THE GULF OF HONDURAS AND THE
N COAST OF NICARAGUA. GUSTY WINDS TO TROPICAL STORM FORCE AND
VERY HEAVY RAIN CAN BE EXPECTED WITHIN THESE RAINBANDS. IN THE
UPPER LEVELS...IVAN IS FLANKED BY A SHORTWAVE TROUGH TO THE WEST
AND STRONG MIDDLE TO UPPER LEVEL RIDGING TO THE EAST.  THIS
PATTERN CONTINUES TO SUPPORT EXCELLENT OUTFLOW IN ALL BUT THE NW
QUADRANT WHERE SOME WLY FLOW OVER THE CENTRAL GLFMEX IS
IMPINGING UPON THE THE SYSTEM. THIS WLY FLOW IS ASSOCIATED WITH
A MID-LATITUDE TROUGH OVER THE SE UNITED STATES WHICH MAY
INCREASE THE WLY SHEAR OVER IVAN DURING THE NEXT FEW DAYS.
OTHERWISE...THE ATMOSPHERE LOOKS GENERALLY FAVORABLE AND IVAN
SHOULD REMAIN A MAJOR HURRICANE AS IT MOVES TOWARD THE W TIP OF
CUBA THIS AFTERNOON AND TONIGHT.

TROPICAL WAVE NEAR BARBADOS ALONG 59W S OF 19N MOVING W 10 KT.
SATELLITE IMAGERY INDICATES THAT THE WAVE HAS BECOME BETTER
ORGANIZED AND 1012 MB LOW HAS DEVELOPED NEAR 15N/16N.
ADDITIONALLY...CONVECTION HAS BECOME MORE CONCENTRATED ABOUT THE
LOW AND SOME BANDING FEATURES ARE NOW EVIDENT IN SATELLITE
IMAGERY. CURRENTLY...SCATTERED TO NUMEROUS MODERATE CONVECTION
FROM 14N-20N BETWEEN 56W-62W INCLUDING MUCH OF THE LEEWARD
ISLANDS.  THE ENVIRONMENT APPEARS FAVORABLE FOR ADDITIONAL
DEVELOPMENT AND A TROPICAL DEPRESSION COULD FORM WITHIN THE NEXT
DAY OR TWO. REGARDLESS OF DEVELOPMENT...THE WAVE WILL BRING
LOCALLY HEAVY RAINS AND GUSTY WINDS TO THE MUCH OF THE LEEWARD
ISLANDS AND E CARIBBEAN TODAY AND TOMORROW.

...TROPICAL WAVES...
WELL-DEFINED TROPICAL WAVE OVER THE E ATLC ALONG 38W S OF 23N
MOVING W 15 KT. THE WAVE CONTINUES TO DEMONSTRATE A CLASSIC
SIGNATURE IN SATELLITE IMAGERY. HOWEVER...THE SYSTEM APPEARS
ELONGATED AND ASSOCIATED CONVECTION IS POORLY ORGANIZED. WIDELY
SCATTERED TO LOCALLY SCATTERED MODERATE LIES WITHIN 150 NM
EITHER SIDE OF THE WAVE AXIS.  THE STRONGEST OF THIS ACTIVITY
RESIDES WITHIN THE ITCZ AND N OF 20N.  WHILE A BIT MORE
CONVECTIVE THAN YESTERDAY...THERE ARE NO SIGNS OF IMMEDIATE
ORGANIZATION.

TROPICAL WAVE NEAR BARBADOS ALONG 59W S OF 19N MOVING W 10 KT.
SEE SPECIAL FEATURES FOR MORE DETAILS.

TROPICAL WAVE OVER THE CENTRAL CARIBBEAN ALONG 72W S OF 22N
MOVING W 10-15 KT.  THE WAVE HAS VIRTUALLY NO SATELLITE
SIGNATURE AND THE PERTURBATION IN NEARBY SOUNDINGS HAS BECOME
QUITE WEAK.  THE CURRENT POSITION IS BASED PRIMARILY UPON
EXTRAPOLATED MOTION.  NO SIGNIFICANT CONVECTION.

...ITCZ...
ITCZ AXIS EXTENDS ALONG 15N10W 8N25W 12N35W 6N52W 10N70W 10N80W.
SCATTERED MODERATE CONVECTION FROM 3N-8N BETWEEN 10W-20W AND
FROM 6N-10N BETWEEN 25W-40W. SCATTERED MODERATE CONVECTION FROM
4N-7N BETWEEN 10W-30W. SCATTERED TO NUMEROUS MODERATE CONVECTION
FROM 7N-11N BETWEEN 35W-41W.

...DISCUSSION...

GULF OF MEXICO...
VIGOROUS SHORTWAVE TROUGH CONTINUES TO MOVE SLOWLY OVER THE EAST
HALF OF THE UNITED STATES WITH A WELL DEFINED UPPER LEVEL LOW
OVER THE TENNESSEE VALLEY.  UPPER LEVEL DYNAMICS/LIFT ASSOCIATED
WITH THE UPPER TROUGH IS SUPPORTING AN AREA OF CLOUDINESS AND
SHOWERS/THUNDERSTORMS OVER THE W GLFMEX AND FLORIDA PANHANDLE.
WATER VAPOR IMAGERY SHOWS THAT BASE OF THE TROUGH AMPLIFIED INTO
THE N GLFMEX OVERNIGHT WITH ASSOCIATED SUBSIDENCE AND DRY AIR
NOW AFFECTING THE N GULF COAST FROM MOBILE BAY WESTWARD TO
TEXAS. HOWEVER...THE TROUGH APPEARS TO HAVE BOTTOMED OUT THIS
MORNING AND IS NOW LIFTING NEWD.  ELSEWHERE...MODERATE
SUBSIDENCE AND DRY AIR AHEAD OF HURRICANE IVAN PREVAILS OVER THE
SE GLFMEX CREATING A TEMPORARY PERIOD OF TRANQUIL CONDITIONS.
THIS WILL GIVE WAY TO THE APPROACHING HURRICANE WITH OUTER
RAINBANDS ALREADY MOVING ACROSS W CUBA INTO THE FLORIDA STRAITS
TO FLORIDA KEYS.  ADDITIONALLY...A SECOND BAND HAS RECENTLY
DEVELOPED AND IS CURRENT AFFECTING N PORTIONS OF THE YUCATAN
PENINSULA. HEAVY RAIN AND GUSTY WINDS TO TROPICAL STORM FORCE
WILL ACCOMPANY THESE WINDS AND CONDITIONS WILL DETERIORATE
RAPIDLY OVER THE NEXT 12-24 HOURS AS POWERFUL HURRICANE IVAN
MOVES INTO THE SE GLFMEX.

CARIBBEAN...
THE MAIN FEATURE OVER THE CARIBBEAN IS HURRICANE IVAN WHICH IS
NEARING THE W TIP OF CUBA. IVAN HAS BEGUN TO MORE NWD DURING THE
LAST 24 HOURS OWING TO THE WEAKENING OF A PERSISTENT MID-LEVEL
RIDGE ACROSS FLORIDA. OUTER RAINBANDS ASSOCIATED WITH IVAN HAVE
BEEN AFFECTING MUCH OF W CUBA DURING THE LAST 24 HOURS WITH
HEAVY RAINS AND GUSTY WINDS.  ELSEWHERE...STRONG MIDDLE TO UPPER
LEVEL RIDGING INDUCED BY OUTFLOW FROM IVAN DOMINATES THE E
TWO-THIRDS OF THE CARIBBEAN WITH ASSOCIATED SUBSIDENCE PRODUCING
RATHER TRANQUIL/DRY WEATHER. HOWEVER...A STRONG TROPICAL WAVE
ABOUT NEAR BARBADOS IS PRODUCING NUMEROUS SHOWERS/THUNDERSTORMS
OVER PORTIONS OF THE LESSER ANTILLES.  THIS ACTIVITY WILL LIKELY
SPREAD WESTWARD INTO THE E CARIBBEAN THIS AFTERNOON AND TONIGHT.

SUBTROPICAL ATLANTIC...
A TROUGH-RIDGE-TROUGH PATTERN PREVAILS ACROSS THE W HALF OF THE
SUBTROPICAL ATLC. THE PATTERN IS COMPRISED OF A MID-UPPER LEVEL
LOW JUST NE OF BERMUDA WITH A TRAILING TROUGH EXTENDING SWD
ALONG 64W/65W TO 20N. ASSOCIATED SUBSIDENCE AND DRY AIR COVERS
THE AREA W OF 65W LIMITING SIGNIFICANT CLOUDS/CONVECTION SAVE
SOME UPPER LEVEL HIGH CLOUDINESS FROM IVAN OVER THE BAHAMAS.  E
OF THE UPPER LOW/TROUGH...DIFFLUENT FLOW IN THE MID-UPPER LEVELS
IS PRODUCING A LARGE AREA OF CLOUDINESS AND SCATTERED SHOWERS/
THUNDERSTORMS FROM 20N-34N BETWEEN 55W-63W. THERE ARE NO SIGNS
OF ORGANIZATION OR DEVELOPMENT WITH THIS ACTIVITY.  A MID-UPPER
LEVEL RIDGE EXISTS OVER THE CENTRAL ATLC ALONG 55W WITH THE
MID-OCEANIC TROUGH LIMITED TO THE E ATLC ALONG 31N36W TO 17N45W.
THE MID-OCEANIC TROUGH IS RETROGRADING WESTWARD WHILE THE W ATLC
TROUGH IS PROGRESSING EWD LEADING TO A SHORTER WAVELENGTH
OVERALL PATTERN.  SCATTERED SHOWERS/THUNDERSTORMS ARE OCCURRING
WITH THE MID-OCEANIC TROUGH FROM 21N-28N BETWEEN 35W-40W. OVER
THE FAR E ATLC...A WELL DEFINED MIDDLE TO UPPER LEVEL RIDGE
EXTENDS WESTWARD FROM AFRICA ALONG 17N/18N TO 35W. THIS RIDGE
HAS BEEN SLOWLY BUILDING WESTWARD IN THE WAKE OF THE
RETROGRADING MID-OCEANIC TROUGH.  AT THE SURFACE...SUBTROPICAL
RIDGE REMAINS DISRUPTED BY THE W ATLC UPPER LOW AND A LOW LEVEL
TROUGH NEAR THE BAHAMAS.  THIS IS PRODUCING A RATHER WEAK PRES
GRADIENT ACROSS THE W ATLC WATERS.

TROPICAL ATLANTIC...
A WELL DEFINED MIDDLE TO UPPER LEVEL RIDGE AXIS EXTENDS WESTWARD
FROM AFRICA ALONG 17N/18N TO 35W. THE RIDGE HAS BEEN SLOWLY
BUILDING WESTWARD ALLOWING DEEP LAYERED ELY FLOW TO RETURN TO
THE E ATLC.  THIS IS GENERALLY A FAVORABLE REGIME FROM TROPICAL
WAVE DEVELOPMENT.  MID-OCEANIC TROUGH DIPS INTO THE TROPICAL
ATLC WATERS BETWEEN 50W-60W. THIS PATTERN IS PRODUCING ENHANCED
ITCZ CONVECTION FROM 35-45W AND SUPPRESSING ITCZ ACTIVITY
BETWEEN 45W-55W.

$$
RHOME/PROSISE


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