[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 161056
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1115 UTC.

...SPECIAL FEATURES...

HURRICANE IVAN IS CENTERED NEAR 30.9N 87.7W OR 40 MILES
NORTHWEST OF PENSACOLA FLORIDA AT 16/0900 UTC MOVING N 12 KT.
MAXIMUM SUSTAINED WIND SPEED IS 100 KT WITH GUSTS TO 120 KT
MAKING IVAN A DANGEROUS CATEGORY 3 HURRICANE ON THE
SAFFIR-SIMPSON SCALE. THE LATEST MINIMUM CENTRAL PRESSURE IS 947
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 MADE LANDFALL NEAR GULF
SHORES ALABAMA AT 0700 UTC. A GRADUAL WEAKENING SHOULD CONTINUE
AS THE HURRICANE MOVES INLAND.  AN EYE IS STILL NOTED ON
SATELLITE IMAGERY AND THERE IS A SOLID SHIELD OF VERY HEAVY
RAINFALL MOVING ONSHORE BETWEEN BILOXI MISSISSIPPI AND CEDAR KEY
FLORIDA EXTENDING AS FAR NORTH AS BIRMINGHAM ALABAMA.  EMBEDDED
TORNADOES ARE POSSIBLE THROUGHOUT THE AREA.

TROPICAL STORM JEANNE IS CENTERED NEAR 18.8N 68.1W NW OF PUERTO
RICO AT 16/0900 UTC MOVING NW 8 KT. MAXIMUM SUSTAINED WIND
SPEED IS 60 KT WITH GUSTS TO 75 KT. ESTIMATED MINIMUM CENTRAL
PRESSURE IS 992 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 NW OF 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 17N-20N BETWEEN 67W-70W...AND FROM
16N-21N BETWEEN 62W-66W.

A STRONG TROPICAL WAVE IS LOCATED W OF THE CAPE VERDE ISLANDS
ALONG 30W S OF 20N MOVING W 15-20 KT...WITH A 1008 MB LOW ALONG
THE AXIS NEAR 11N30W. 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 TROUGH 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
29W-34W.

...TROPICAL WAVES...

SEE SPECIAL FEATURES FOR LOW AND TROPICAL WAVE ALONG 30W.

CENTRAL ATLC TROPICAL WAVE IS ALONG 47W S OF 20N MOVING W 15 KT.
AN EXTENSIVE SAHARAN AIR LAYER HAS OVERTAKEN THE WAVE AND THE
LEADING EDGE IS ORIENTED ALONG  32N40W 22N51W 8N43W. THE WAVE
ITSELF IS BEING TRACKED ALONG A BATCH OF TSTMS NEAR THE GREATEST
LOW-LEVEL ROTATION...WITH ISOLATED MODERATE CONVECTION FROM
10N-16N BETWEEN 45W-49W.

A WEAK TROPICAL WAVE IS CROSSING PARTS OF CENTRAL AMERICA ALONG
88W S OF 17N MOVING W 15 KT. THE WAVE IS TRIGGERING SCATTERED
MODERATE CONVECTION OVER THE EASTERN PACIFIC.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 16N1W 15N15W 9N40W 10N60W 13N70W
10N86W.  WIDELY SCATTERED MODERATE CONVECTION IS ALONG THE COAST
OF W AFRICA FROM 3N-17N BETWEEN 11W-20W.  SIMILAR CONVECTION IS
FROM 6N-10N BETWEEN 34W-44W...AND FROM 10N-13N BETWEEN
50W-57W.

...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 BETWEEN
THE BAHAMAS AT 73W TO THE CENTRAL GULF OF MEXICO NEAR 93W.  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.

REMAINDER OF CARIBBEAN...
BROAD NELY FLOW COVERS THE W CARIBBEAN W OF 80W.  A CYCLONIC
CIRCULATION IS OVER THE CENTRAL CARIBBEAN NEAR 15N73W.  UPPER
LEVEL ANTICYCLONIC OUTFLOW IS OVER THE E CARIBBEAN DUE TO T.S.
JEANNE FROM 14N-23N BETWEEN 56W-70W.  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.

SUBTROPICAL ATLANTIC...
A BROAD MID/UPPER LEVEL TROUGH CONTINUES TO SINK SWD OVER THE W
ATLC WATERS ALONG 32N53 2363W. 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
3051 26N58W 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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