[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 160552
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT THU 16 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0515 UTC.

...SPECIAL FEATURES...

HURRICANE IVAN IS CENTERED NEAR 29.3N 88.1W OR 40 MILES S OF
THE ALABAMA COASTLINE AT 16/0300 UTC MOVING N 10 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 933 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 N SEMICIRCLE. THE LAST FEW VISIBLE
IMAGES PORTRAY A SPECTACULAR STORM...PRACTICALLY SYMMETRIC IN
ALL QUADRANTS WITH OUTFLOW RADIATING OUTWARD IN ALL DIRECTIONS.
BUOY 42040 JUST E OF THE MISSISSIPPI DELTA HAS BEEN CONSISTENTLY
REPORTING WAVE HEIGHTS UP TO 50 FT WITH A REPORTED PRESSURE OF
967 MB AT 0500 UTC. NUMEROUS MODERATE CONVECTION IS LOCATED IN
THE CORE FROM 27N-31N BETWEEN 86W-91W WITH OTHER SCATTERED
MODERATE WITHIN A SPIRAL BAND MOVING INTO THE FLORIDA PANHANDLE.
THE WELL-DEFINED EYE IS IN RADAR RANGE AND THERE IS A SOLID
SHIELD OF VERY HEAVY RAINFALL MOVING ONSHORE BETWEEN
APALACHICOLA FLORIDA AND GRAND ISLE LOUISIANA...WITH POSSIBLE
TORNADOES TO THE W AND S OF TALLAHASSEE FLORIDA.

TROPICAL STORM JEANNE IS CENTERED NEAR 18.5N 67.3W 0OFF NW
PUERTO RICO AT 16/0300 UTC MOVING WNW 8 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. THE CONVECTION
ASSOCIATED WITH JEANNE HAS BEEN FOCUSED IN TWO DISTINCT
CLUSTERS... ONE NEAR WESTERN PUERTO RICO AND THE OTHER A LITTLE
FARTHER E OVER THE VIRGIN ISLANDS.  SATELLITE RAINFALL ESTIMATES
INDICATE THAT OVER 10" OF ACCUMULATED RAIN IS POSSIBLE OVER
THESE ISLANDS AS JEANNE SLOWLY MOVES TO THE WNW.  NUMEROUS
STRONG CONVECTION IS FROM 18N-20N BETWEEN 67W-69W...AND FROM
16N-20N BETWEEN 63W-66W.

A STRONG TROPICAL WAVE IS LOCATED JUST W OF THE CAPE VERDE
ISLANDS ALONG 27W/28W S OF 16N MOVING W 15-20 KT...WITH A 1009
MB LOW ALONG THE AXIS NEAR 11N27.5W. THE CONVECTION NEAR THE LOW
IS MOSTLY N AND W OF THE CENTER. 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. WIDELY SCATTERED MODERATE CONVECTION IS FROM 10N-15N
BETWEEN 25W-30W.

...TROPICAL WAVES...

SEE SPECIAL FEATURES FOR LOW AND TROPICAL WAVE ALONG 27W/28W.

CENTRAL ATLC TROPICAL WAVE IS ALONG 45W S OF 20N 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 ISOLATED 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
87W S OF 17N MOVING W 15 KT. THE WAVE IS TRIGGERING SCATTERED
MODERATE CONVECTION OVER NICARAGUA...AND COSTA RICA FROM 7N-12N
BETWEEN 85W-89W.

...ITCZ...

ITCZ AXIS IS CENTERED 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 13W-19W. SCATTERED MODERATE
CONVECTION IS FROM 8N-13N BETWEEN 30W-33W...AND FROM 5N-8N
BETWEEN 33W-46W.

...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 OUTFLOW 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 TROUGH 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 EARLY THIS 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 TROUGH
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 TROUGH CONTINUES TO SINK SWD OVER THE W
ATLC WATERS ALONG 32N57W 24N63W. MODERATE/STRONG SUBSIDENCE
EXTENDS UP TO 500 NM NW AND 120 NM SE OF THE TROUGH AXIS...AND
THE TROUGH IS ACTUALLY PRODUCING A SIGNIFICANT OUTFLOW JET TO
THE NE OF T.S. JEANNE. A REMNANT SFC TROUGH IS ALIGNED ALONG
31N50W 27N56W 25N63W WITH ONLY ISOLATED SHOWERS UP TO 90 NM E OF
THE AXIS. FARTHER E...A LOW-AMPLITUDE WAVE-LIKE PATTERN IS
BETWEEN 25W AND 55W WITH TWO RIDGES ALONG 38W AND 50W AND A
SHORTWAVE TROUGH SANDWICHED IN BETWEEN ALONG 47W. A MUCH DEEPER
LONGWAVE TROUGH IS TILTED FROM THE W MEDITERRANEAN SEA SWWD TO
18N23W 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 56W
WITH MUCH DRIER AIR LOCATED BETWEEN 45W AND 56W. THE RIDGE IS
INTERRUPTED SLIGHTLY BY AN UPPER TROUGH OVER THE
SUBTROPICS...BUT THE RIDGE IS RE-ESTABLISHED W OF THE CAPE VERDE
ISLANDS WITH AN UPPER HIGH CENTERED NEAR 19N36W AND EXTENDING
EWD TO THE SENEGAL/GUINEA-BISSAU BORDER.

$$
FORMOSA


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