[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 151804 RRA
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT WED 15 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
1745 UTC.

...SPECIAL FEATURE...
HURRICANE IVAN IS CENTERED NEAR 27.8N 88.2W OR 170 MILES S OF
THE MOUTH OF THE MISSISSIPPI AT 15/1800 UTC. IVAN IS MOVING
TOWARD THE NORTH AT 12 KT. MAXIMUM SUSTAINED WIND SPEED IS 115
KT WITH HIGHER GUSTS MAKING IVAN A DANGEROUS CATEGORY 4
HURRICANE ON THE SAFFIR-SIMPSON SCALE. MINIMUM CENTRAL PRESSURE
HAS RISEN TO 939 MB. SEE LATEST NHC PUBLIC ADVISORY OR NHC
FORECAST/ ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT4/WTNT34 KNHC
FOR MORE DETAILS. THE SATELLITE SIGNATURE ASSOCIATED WITH IVAN
HAS BEEN IMPROVING TODAY. CLOUD TOP TEMPERATURES HAVE COOLED AND
THE EYE HAS BECOME MORE DISTINCT AND NEAR CLOUD FREE IN LATEST
RAPID SCAN VISIBLE IMAGERY. INTENSE CONVECTION IS NOW WITHIN
60-75 NM OVER THE N SEMICIRCLE AND WITHIN 90-120 NM OVER THE S
SEMICIRCLE. OUTER RAINBANDS ARE AFFECTING THE N GULF COAST FROM
THE FLORIDA BIG BEND AREA WESTWARD TO THE SE TIP OF LOUISIANA.
LATEST RADAR AND SURFACE OBSERVATIONS INDICATE THAT HEAVY RAINS
AND GUSTY WINDS TO TROPICAL STORM FORCE ACCOMPANY THESE BANDS
AND CONDITIONS WILL DETERIORATE RAPIDLY THIS AFTERNOON. IN THE
MIDDLE TO UPPER LEVELS...IVAN IS MOVING AROUND THE W PERIPHERY
OF A LARGE RIDGE OVER THE W ATLC AND IS LOCATED E OF A
PERSISTENT UPPER LEVEL SHEAR AXIS CURRENTLY OVER THE W GLFMEX.
THIS PATTERN HAD BEEN PRODUCING SOME SHEAR OVER IVAN BUT SHEAR
NOW APPEARS TO BE WEAKENING. ACCORDINGLY UPPER LEVEL OUTFLOW IS
IMPROVING IN ALL BUT THE SW QUADRANTS WHERE SOME DRY AIR IS
NOTED IN WATER VAPOR IMAGERY OVER THE W GLFMEX.

TROPICAL STORM JEANNE IS CENTERED NEAR 18.1N 66.1W OR 55 MILES
SSW OF SAN JUAN PUERTO RICO 15/1800 UTC. JEANNE IS MOVING WNW AT
7 KT. MAXIMUM SUSTAINED WIND SPEED IS 60 KT WITH GUSTS TO 70 KT
AND THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 991 MB.  SEE
LATEST NHC PUBLIC ADVISORY OR NHC FORECAST/ADVISORY UNDER
AWIPS/WMO HEADERS MIATCPAT1/WTNT31 KNHC OR MIATCMAT1/WTNT21 KNHC
FOR MORE DETAILS. AFTER LOOKING A BIT RAGGED IN SATELLITE
IMAGERY THIS MORNING...JEANNE NOW APPEARS TO BE BECOMING BETTER
ORGANIZED DESPITE MOVING OVER E PUERTO RICO. THE LOW LEVEL
CIRCULATION IS NOT QUITE AS EXPOSED INDICATING SOME RELAXATION
OF THE VERTICAL SHEAR CURRENTLY AFFECTING THE SYSTEM.
ADDITIONALLY...RADAR DATA FROM SAN JUAN SHOWS DEEP CONVECTION
WRAPPING AROUND THE S SIDE.  INTENSE CONVECTION ASSOCIATED WITH
JEANNE HAS BEEN AFFECTING PUERTO RICO DURING THE LAST SEVERAL
HOURS WHILE A WELL-DEFINED BAND TO THE EAST THE LEEWARD ISLANDS
FROM GUADALOUPE NWD. SCATTERED TO LOCALLY NUMEROUS STRONG
CONVECTION FROM 14.5N TO 20N BETWEEN 62W-67W. JEANNE IS LOCATED
JUST E OF AN UPPER LEVEL TROUGH/LOW OVER HISPANIOLA AND THIS
FEATURE IS EXPECTED TO PRODUCE A MARGINALLY FAVORABLE UPPER
ENVIRONMENT OVER THE NEXT DAY OR SO.

TROPICAL WAVE OVER THE FAR E ATLC NEAR THE CAPE VERDE ISLANDS
ALONG 25W MOVING 15-20 KT. THE WAVE IS ACCOMPANIED BY A 1010 MB
LOW NEAR 10N/11N.  LATEST METSAT-8 SATELLITE IMAGERY INDICATES
THAT THE WAVE HAS BECOME BETTER ORGANIZED WITH INCREASING DEEP
CONVECTION. THE WAVE/LOW IS LOCATED ON THE S SIDE OF A LARGE
MID-LEVEL RIDGE AND CONDITIONS APPEAR FAVORABLE FOR THIS SYSTEM
TO BECOME A TROPICAL DEPRESSION OVER THE NEXT DAY OR SO.
SCATTERED MODERATE CONVECTION FROM 10N-13N BETWEEN 23W-30W.
WIDELY SCATTERED MODERATE CONVECTION WITHIN THE ITCZ FROM 6N-10N
BETWEEN 20W-35W.

...TROPICAL WAVES...
SEE SPECIAL FEATURES FOR TROPICAL WAVE ALONG 25W.

TROPICAL WAVE OVER THE CENTRAL ATLC ALONG 43W S OF 21N MOVING W
15 KT. THE WAVE IS CURRENTLY BEING OVERTAKEN BY A SAHARAN AIR
LAYER FROM THE EAST.  THUS...THE SATELLITE SIGNATURE IS BECOMING
DOMINATED BY THE LEADING EDGE OF THE SAL FRONT. THE CURRENT
POSITION IS BASED ON AN AREA OF LOW LEVEL TURNING NEAR THE ITCZ
RATHER THAN THE SAL FRONT ITSELF WHICH IS NEARING 50W. GIVEN THE
RELATIVELY DRY/STABLE AIR ASSOCIATED WITH THE SAL...THE WAVE
WILL BE LOCATED WITHIN AN UNFAVORABLE ENVIRONMENT FOR
DEVELOPMENT.

TROPICAL WAVE OVER OVER CENTRAL AMERICA NEAR NICARAGUA/HONDURAS
ALONG 85W S OF 18N MOVING W 15 KT. THE WAVE CONTINUES TO HAVE
VIRTUALLY NO SATELLITE SIGNATURE WITH NO ASSOCIATED DEEP
CONVECTION. THE CURRENT POSITION IS BASED PRIMARILY UPON
EXTRAPOLATED MOTION.  WIDELY SCATTERED MODERATE CONVECTION
WITHIN THE ITCZ FROM 6N-10N BETWEEN 20W-35W AND FROM 8N-13N
BETWEEN 48W-58W.

...ITCZ...
ITCZ AXIS ALONG 14N10W 11N20W 10N35W 11N50W 15N60W...THEN
DISRUPTED BY T.S. JEANNE NEAR PUERTO RICO.  ITCZ BECOME
RE-ESTABLISHED NEAR 11N70W SW TO 8N80W.

...DISCUSSION...

GULF OF MEXICO...
SEE SPECIAL FEATURES FOR WEATHER ASSOCIATED WITH HURRICANE IVAN.
SHORTWAVE TROUGH OVER THE E UNITED STATES CONTINUES TO LIFT NEWD
THROUGH THE MID-ATLANTIC REGION WHILE A SECOND SHORTWAVE TROUGH
MOVES EWD OVER THE CENTRAL UNITED STATES. IN BETWEEN...IVAN IS
MOVING N/NW TOWARD THE N GULF COAST AROUND THE W PERIPHERY OF A
LARGE MID-LEVEL RIDGE OVER THE W ATLC.  HEAVY RAIN AND GUSTY
WINDS TO TROPICAL STORM FORCE WILL SPREAD INLAND FROM SE
LOUISIANA TO THE FLORIDA BIG BEND AREA THIS AFTERNOON AND
CONDITIONS WILL DETERIORATE RAPIDLY OVER THE NEXT 12-24 HOURS AS
POWERFUL HURRICANE IVAN APPROACHES. ELSEWHERE...WATER VAPOR
IMAGERY SHOWS MID-UPPER LEVEL DRYING ASSOCIATED WITH CONFLUENT
FLOW BETWEEN OUTFLOW FROM IVAN AND A PERSISTENT SHEAR AXIS OVER
THE W GLFMEX.

CARIBBEAN...
IN THE EASTERN CARIBBEAN...TROPICAL STORM JEANNE CONTINUES TO
MOVE WESTWARD WITH THE CENTER NOW OVER E PUERTO RICO. LATEST
SATELLITE SHOWS JEANNE IS BECOME A LITTLE BETTER ORGANIZED AS
CONVECTION RECENTLY BLOSSOMED OVER PUERTO RICO. STRONG SHOWERS
AND TSTMS ARE NOTED WITH A BAND TO THE EAST OVER THE LEEWARD
ISLANDS. THIS ACTIVITY WILL LIKELY CONTINUE TO AFFECT THE NE
PORTIONS OF THE E CARIBBEAN THIS AFTERNOON AND TONIGHT AS JEANNE
SLOWLY MOVES WNW. ELSEWHERE...STRONG MIDDLE TO UPPER LEVEL RIDGE
EXTENDS FROM THE W ATLC ACROSS CUBA INTO THE NW CARIBBEAN SEA.
UW-CIMSS SATELLITE DERIVED INDICATE NELY FLOW TO 60 KT W OF
HISPANIOLA. THIS IS PRODUCING GENERALLY DRY/TRANQUIL WEATHER
WITH THE ONLY CLOUDS OF NOTE BEING CIRRUS OUTFLOW FANNING OUT
FROM IVAN TO THE NORTH.

SUBTROPICAL ATLANTIC...
LARGE MIDDLE TO UPPER LEVEL RIDGE DOMINATES THE W ATLC BETWEEN
BERMUDA AND THE SE UNITED STATES.  WHILE NOT PRODUCING
SIGNIFICANT WEATHER...THE FLOW AROUND THE RIDGE IS ALLOWING HIGH
CLOUDINESS FROM HURRICANE IVAN OVER THE GLFMEX TO FAN OUTWARD W
OF 70W.  FURTHER E...LARGE UPPER LEVEL TROUGH JUST E OF BERMUDA
IS AMPLIFYING SWD. STRONG SUBSIDENCE BLANKETS THE AREA N OF 25N
BETWEEN 55W-70W.  SW FLOW AHEAD OF THIS TROUGH IS ALLOWING
MID-UPPER LEVEL MOISTURE AND HIGH CLOUDINESS FROM T.S. JEANNE TO
STREAM NEWD ACROSS THE CENTRAL ATLC.  THIS MOISTURE CONTINUES UP
AND OVER A LARGE RIDGE IN THE E ATLC LEAVING THE E HALF OF THE
ATLC UNDER DRY/TRANQUIL CONDITIONS.

TROPICAL ATLANTIC...
A WELL DEFINED MIDDLE TO UPPER LEVEL RIDGE AXIS EXTENDS WESTWARD
FROM AFRICA ALONG 12N/13N TO 42W. THE RIDGE HAS BEEN SLOWLY
BUILDING WESTWARD DURING THE LAST SEVERAL DAYS ALLOWING DEEP
LAYERED ELY FLOW TO RETURN TO THE E ATLC.  HOWEVER...A LARGE
AMPLITUDE TROUGH IS NOW DIGGING OVER THE E ATLC AND W AFRICA N
OF 20N E OF 30W SUPPRESSING THE RIDGE SWD AND ERODING THE E PART
NEAR AFRICA. ELSEWHERE...MID-OCEANIC UPPER LEVEL TROUGH DIPS
INTO THE TROPICAL ATLC WATERS BETWEEN 45W-55W.  THIS PATTERN IS
ENCOURAGING ITCZ CONVECTION E OF THE LESSER ANTILLES.

$$
RHOME


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