[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 160001
TWDAT

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

...SPECIAL FEATURES...

HURRICANE IVAN IS CENTERED NEAR 28.9N 88.2W OR 100 MILES S OF
THE ALABAMA COASTLINE AT 16/0000 UTC MOVING N 12 KT. MAXIMUM
SUSTAINED WIND SPEED IS 115 KT WITH GUSTS TO 140 KT MAKING IVAN
A DANGEROUS CATEGORY 4 HURRICANE ON THE SAFFIR-SIMPSON SCALE.
THE LATEST MINIMUM CENTRAL PRESSURE MEASURED BY A NOAA HURRICANE
HUNTER IS 931 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 NOT GIVING UP
ANY OF ITS POWER AS IT NEARS THE COAST OF ALABAMA AND
MISSISSIPPI. THE EYE HAS BEEN MAINTAINED AT A CONSISTENT 25-30
NM WIDE WITH VERY STRONG CONVECTION WRAPPED ENTIRELY AROUND THE
CENTER...ESPECIALLY OVER THE W SEMICIRCLE. THE LAST FEW VISIBLE
IMAGES PORTRAY A SPECTACULAR STORM...PRACTICALLY SYMMETRIC IN
ALL QUADRANTS WITH OUTFLOW RADIATING OUTWARD IN ALL DIRECTIONS.
WHAT HAS BEEN SO EERIE IS THAT BUOY 42040 JUST E OF THE
MISSISSIPPI DELTA HAS BEEN CONSISTENTLY REPORTING WAVE HEIGHTS
UP TO 50 FT THIS AFTERNOON WITH A REPORTED PRESSURE OF 963 MB AT
2300 UTC! NUMEROUS MODERATE CONVECTION IS LOCATED IN THE CORE
FROM 26N-31N BETWEEN 86W-91W WITH OTHER SCATTERED MODERATE
WITHIN A SPIRAL BAND MOVING INTO THE FLORIDA PANHANDLE. THE
WELL-DEFINED EYE HAS COME INTO RADAR RANGE AND THERE IS JUST
ABOUT A SOLID SHIELD OF VERY HEAVY RAINFALL MOVING ONSHORE
BETWEEN APALACHICOLA FLORIDA AND GRAND ISLE LOUISIANA...WITH
THAT SPIRAL BAND WITH POSSIBLE TORNADOES TO THE W AND S OF
TALLAHASSEE FLORIDA.

TROPICAL STORM JEANNE IS CENTERED NEAR 18.5N 67.0W OR OVER NW
PUERTO RICO NEAR ISABELA AT 16/0000 UTC MOVING W 9 KT. MAXIMUM
SUSTAINED WIND SPEED IS 55 KT WITH GUSTS TO 65 KT. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 993 MB. SEE LATEST NHC PUBLIC
ADVISORY OR NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCPAT1/WTNT31 KNHC OR MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS.
FOR MOST OF THE DAY...THE CONVECTION ASSOCIATED WITH JEANNE HAS
BEEN FOCUSED IN TWO DISTINCT CLUSTERS...NEAR PUERTO RICO AND THE
VIRGIN ISLANDS AND A LITTLE FARTHER S OVER THE E CARIBBEAN
WATERS. RECENTLY...THE NRN CLUSTER SEEMS TO HAVE BEEN WRAPPING
UP A LITTLE MORE AND STRONG CONVECTIVE BANDING IS DEVELOPING
OVER THE VIRGIN ISLANDS. SCATTERED MODERATE/STRONG CONVECTION IS
FROM 14.5N-20N BETWEEN 64W-68W WITH TRAILING WIDELY SCATTERED
MODERATE JUST E OF THE NRN LEEWARD ISLANDS FROM 15.5N-21N
BETWEEN 59W-64W. RADAR IMAGERY FROM SAN JUAN SHOWS THE CENTER OF
CIRCULATION MOVING OFFSHORE THE NW CORNER OF PUERTO RICO WITH
VERY HEAVY RAINFALL OVER THE ISLAND AND ALONG A BAND OF TRAILING
TSTMS THAT EXTEND OVER ST. THOMAS...ST. CROIX...VIEQUES...
CULEBRA...AND THE E SHORE OF PUERTO RICO. SATELLITE RAINFALL
ESTIMATES INDICATE THAT OVER 10" OF ACCUMULATED RAIN IS POSSIBLE
OVER THESE ISLANDS AS JEANNE SLOWLY MOVES TO THE WNW.

A STRONG TROPICAL WAVE IS LOCATED JUST W OF THE CAPE VERDE
ISLANDS ALONG 26W/27W S OF 15N MOVING W 15-20 KT...WITH A 1009
MB LOW ALONG THE AXIS NEAR 10.5N26W. THE CONVECTION NEAR THE LOW
HAS BEEN ORGANIZING THROUGH THE DAY BUT IT IS NOW REMOVED ABOUT
120 NM TO THE NW OF THE CENTER OF CIRCULATION ALIGNED ALONG A
LINEAR NE/SW BAND. THE SYSTEM IS MOVING AWAY FROM STRONG
WESTERLIES AT THE BASE OF A TROF OFF THE MOROCCAN COAST...AND
THE LOWER SHEAR VALUES TO THE W HAVE MADE THE ENVIRONMENT
FAVORABLE FOR TROPICAL DEVELOPMENT OVER THE NEXT 36 HOURS.
SCATTERED MODERATE CONVECTION IS FROM 9N-14N BETWEEN 26W-32W.

...TROPICAL WAVES...

SEE SPECIAL FEATURES FOR LOW AND TROPICAL WAVE ALONG 26W/27W.

CENTRAL ATLC TROPICAL WAVE ALONG 44W S OF 19N MOVING W 15 KT. AN
EXTENSIVE SAHARAN AIR LAYER HAS OVERTAKEN THE WAVE AND THE
LEADING EDGE IS ORIENTED ALONG A LINE DIAGONAL ACROSS THE
AXIS...ALONG 26N50W 20N50W 8N40W. THE WAVE ITSELF IS BEING
TRACKED ALONG A BATCH OF TSTMS NEAR THE GREATEST LOW-LEVEL
ROTATION...WITH WIDELY SCATTERED MODERATE CONVECTION FROM
13N-16N BETWEEN 43W-45W. HOWEVER...THE LEADING EDGE OF THE DRY
AIR IS ALSO PRODUCING ISOLATED SHOWERS/TSTMS FROM 17N-26N
BETWEEN 45W-50W.

A WEAK TROPICAL WAVE IS CROSSING PARTS OF CENTRAL AMERICA ALONG
86W S OF 17N MOVING W 15 KT. THE WAVE IS TRIGGERING MAINLY
DIURNAL TSTMS OFF THE WESTERN SLOPES OF THE MTNS IN HONDURAS...
NICARAGUA...AND COSTA RICA WITH LITTLE ASSOCIATED WEATHER OVER
THE CARIBBEAN WATERS. SCATTERED MODERATE CONVECTION S OF 13N W
OF 84W AND ACROSS W PANAMA AND COSTA RICA.

...ITCZ...

ITCZ AXIS ALONG 7N15W 12N25W...THEN ALONG 8N28W 8N32W
13N41W...THEN ALONG 8N45W 14N60W...THEN ALONG 8N64W 10N85W. A
STRONG SQUALL LINE IS MOVING OFF THE AFRICAN COAST WITH
SCATTERED MODERATE/STRONG CONVECTION EXTENDING FROM SENEGAL TO
GUINEA FROM 7.5N-16N BETWEEN 10W-17W. ISOLATED SHOWERS/TSTMS 200
NM SW OF THE AXIS BETWEEN 15W-24W. SCATTERED MODERATE FROM
5N-10N BETWEEN 35W-45W. ISOLATED MODERATE WITHIN 100 NM S OF THE
AXIS BETWEEN 47W-58W. WIDELY SCATTERED MODERATE OVER NRN
VENEZUELA AND N COLOMBIA.

...DISCUSSION...

GULF OF MEXICO...W ATLC...AND NW CARIBBEAN...
HURRICANE IVAN IS ESSENTIALLY CREATING ITS OWN UPPER LEVEL
ENVIRONMENT OVER THE AREA WITH A STRONG UPPER LEVEL HIGH
DEVELOPING JUST E OF THE STORM NEAR THE FLORIDA KEYS...AND
RIDGING EXTENDING NWD INTO GEORGIA. THIS BROAD RIDGE IS BRINGING
MOST OF THE CIRRUS EXHAUST FROM IVAN OVER THE W ATLC WATERS...
THEN SWWD ACROSS CUBA TO PARTS OF NRN CENTRAL AMERICA. THE
HURRICANE IS BOUNDED ON ITS W SIDE BY A LARGE AREA OF DRY AIR
OVER THE W GULF AND SRN U.S. PLAINS...BUT IT DOESN'T APPEAR THIS
DRY AIR IS BEING ENTRAINED INTO THE CIRCULATION (PROBABLY
BECAUSE THERE IS LITTLE SHEAR AT THIS TIME TO MAKE THE HURRICANE
VULNERABLE). THERE IS A WEAK SHORTWAVE TROF LINGERING OVER THE W
GULF...BUT THIS SEEMS TO BE AN ARTIFACT OF WLY FLOW OVER MEXICO
IMPINGING ON THE SLY OUTFLOW OF HURRICANE IVAN. LOOKING
UPSTREAM...THE LONGWAVE TROF WE WERE WATCHING YESTERDAY OVER THE
ROCKY MTN STATES HAS LIFTED INTO THE DAKOTAS AND STRONG UPPER
LEVEL WLY FLOW HAS DEVELOPED ACROSS THE WESTERN UNITED STATES.
UNFORTUNATELY...IVAN IS POISED TO MAKE LANDFALL ALONG THE N GULF
COAST TONIGHT OR EARLY TOMORROW MORNING AND WILL NOT FEEL THE
DETRIMENTAL AFFECTS OF THESE WINDS SOON ENOUGH.

REMAINDER OF CARIBBEAN...
E OF THE BROAD NELY FLOW COVERING THE W CARIBBEAN...AN INVERTED
UPPER LEVEL TROF HAS DEVELOPED FROM LAKE MARACAIBO NWD TO THE
MONA PASSAGE...OR JUST AHEAD OF T.S. JEANNE. UPPER LEVEL OUTFLOW
IS EXPANDING TO THE NW OF JEANNE AROUND THE APEX OF THE TROF BUT
IT APPEARS THAT SWLY SHEAR IS UNDERCUTTING THE SW QUADRANT OF
THE SYSTEM WITH PERHAPS SOME DRY AIR BEING ENTRAINED BETWEEN THE
CENTRAL CORE OF CONVECTION AND A LAGGING FEEDER BAND. ASIDE FROM
CONVECTION ASSOCIATED WITH JEANNE...WIDELY SCATTERED MODERATE
CONVECTION HAS DEVELOPED OVER PARTS OF HISPANIOLA AND E CUBA.

SUBTROPICAL ATLANTIC...
A BROAD MID/UPPER LEVEL TROF CONTINUES TO SINK SWD OVER THE W
ATLC WATERS ALONG 32N54W 25N66W. MODERATE/STRONG SUBSIDENCE
EXTENDS UP TO 500 NM NW AND 120 NM SE OF THE TROF AXIS...AND THE
TROF IS ACTUALLY PRODUCING A SIGNIFICANT OUTFLOW JET TO THE NE
OF T.S. JEANNE. A REMNANT SFC TROF IS ALIGNED ALONG 31N52W
26N58W 25N64W WITH ONLY ISOLATED SHOWERS UP TO 90 NM E OF THE
AXIS. FARTHER E...A LOW-AMPLITUDE WAVE-LIKE PATTERN IS BETWEEN
26W AND 50W WITH TWO RIDGES ALONG 31W AND 45W AND A SHORTWAVE
TROF SANDWICHED IN BETWEEN ALONG 36W. A MUCH DEEPER LONGWAVE
TROF IS TILTED FROM THE W MEDITERRANEAN SEA SWWD TO 20N23W WITH
SHORTWAVES PLOWING SWD ACROSS THE CANARY ISLANDS THEN INTO NW
AFRICA.

TROPICAL ATLANTIC...
WEAK MID/UPPER LEVEL RIDGING IS DEVELOPING TO THE E OF T.S.
JEANNE WITH THE AXIS EXTENDING FROM NEAR GUADELOUPE EWD TO
18N50W. THE OUTFLOW FROM JEANNE ONLY EXTENDS AS FAR E AS 58W
WITH MUCH DRIER AIR LOCATED BETWEEN 45W AND 58W. THE RIDGE IS
INTERRUPTED SLIGHTLY BY AN UPPER TROF OVER THE SUBTROPICS...BUT
THE RIDGE IS RE-ESTABLISHED W OF THE CAPE VERDE ISLANDS WITH AN
UPPER HIGH CENTERED NEAR 17N37W AND EXTENDING EWD TO THE
SENEGAL/GUINEA-BISSAU BORDER.

$$
BERG




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