[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 172341
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI 17 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...

TROPICAL DEPRESSION JEANNE IS ALMOST STATIONARY NEAR 20.1N
71.8W...OR JUST N OF THE HAITI COAST AND 100 MILES SSW OF GRAND
TURK ISLAND...AT 18/0000 UTC. MAXIMUM SUSTAINED WIND SPEED HAS
DECREASED TO 30 KT WITH GUSTS TO 40 KT. MINIMUM CENTRAL PRESSURE
REPORTED BY AN AIR FORCE RECONNAISSANCE AIRCRAFT IS 1000 MB. SEE
LATEST NHC PUBLIC ADVISORY OR NHC FORECAST/ADVISORY UNDER AWIPS/
WMO HEADERS MIATCPAT1/WTNT31 KNHC OR MIATCMAT1/WTNT21 KNHC FOR
MORE DETAILS. THERE IS SOME DEBATE AS TO THE WHY'S OF
WEAKENING...BUT IT DOES APPEAR THAT JEANNE HAS SUCCUMBED TO BOTH
THE RUGGED TERRAIN OF HISPANIOLA AND WLY SHEAR TO THE N OF AN
UPPER LEVEL HIGH CENTERED ABOUT 120 NM S OF THE ISLAND. NOW THE
DRY AIR OVER THE BAHAMAS IS APPLYING A SECOND PUNCH AND WILL
MAKE IT HARD FOR CONSISTENT CONVECTION TO REDEVELOP NEAR THE
CENTER...AT LEAST IN THE SHORT TERM. THIS IS HIGHLY REMINISCENT
OF HURRICANE DEBBY OF 2000...WHICH HAD A SIMILAR FATE NEAR
HISPANIOLA AND NEVER RECOVERED...ALTHOUGH IT IS TRUE THAT JEANNE
IS MOVING A LOT SLOWER THAN DEBBY WAS AT THE TIME. CURRENTLY...A
FEW TSTMS ARE POPPING JUST E OF THE CENTER WITH SCATTERED
MODERATE CONVECTION FROM 19N-21N BETWEEN 69W-72W...BUT OF MORE
CONCERN IS THE PERSISTENT BAND OF CONVECTION THAT CONTINUES TO
PUMMEL THE AREA FROM THE DOMINICAN REPUBLIC TO THE VIRGIN
ISLANDS. NUMEROUS STRONG CONVECTION IS WITHIN 60 NM OF A LINE
FROM 16.5N70.5W 20N66W AND RADAR IMAGERY SHOWS THIS BAND HUGGING
THE E TIP OF HISPANIOLA AND OVER THE MONA PASSAGE. OTHER
SCATTERED MODERATE CONVECTION EXTENDS FROM E PUERTO RICO AND THE
U.S./BRITISH VIRGIN ISLANDS NWD TO 20N BETWEEN 63.5W-66W.

TROPICAL STORM KARL IS CENTERED NEAR 13.4N 36.4W...OR ABOUT 850
MILES W OF THE CAPE VERDE ISLANDS...AT 17/2100 UTC MOVING NW 12
KT. MAXIMUM SUSTAINED WIND SPEED IS 55 KT WITH GUSTS TO 65 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 994 MB. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC
FOR MORE DETAILS. INFRARED SATELLITE IMAGERY INDICATES THAT KARL
IS DEVELOPING A STRONG CORE OF CONVECTION OVER ITS LOW-LEVEL
CENTER WITH A SIGNIFICANT BAND WRAPPING AROUND THE W SEMICIRCLE.
THE UPPER LEVEL OUTFLOW IS MOST IMPRESSIVE TO THE N AND NE OF
THE SYSTEM AND IMPROVING TO THE SW. KARL IS LAGGING TO THE E OF
A LARGE AREA OF DRY SAHARAN AIR...BUT WITH ITS FORECAST TRACK
TURNING IT TO THE N OVER THE ATLC IT WILL PROBABLY BE ABLE TO
ESCAPE THE BRUNT OF THE UNFAVORABLE ENVIRONMENT. SCATTERED
MODERATE/STRONG CONVECTION FROM 11N-15N BETWEEN 35W-41W. WIDELY
SCATTERED MODERATE ELSEWHERE FROM 13N-18N BETWEEN 30W-38W.

...TROPICAL WAVES...

A NEW TROPICAL WAVE HAS BEEN INTRODUCED JUST E OF THE CAPE VERDE
ISLANDS ALONG 22W S OF 20N MOVING W 10-15 KT. METEOSAT-8 VISIBLE
IMAGERY SHOWS A NICE CIRCULATION CENTERED JUST SE OF THE ISLANDS
BUT THERE HAS BEEN NO EVIDENCE AS OF YET THAT THIS IS AT THE
SURFACE. HOPEFULLY THE UPCOMING QSCAT PASS WILL PROVIDE FURTHER
INFORMATION. REGARDLESS...HOVMOELLER CHARTS SHOW A TRACKABLE
CLOUD MASS ACROSS W AFRICA AND THE BAMAKO AND DAKAR SOUNDINGS
BOTH SHOW WEAK WAVE PASSAGES YESTERDAY. ISOLATED MODERATE
CONVECTION IS FROM 10N-15.5N BETWEEN 20W-26W WITH MORE SCATTERED
TSTMS FARTHER S ALONG THE ITCZ.

TROPICAL WAVE LOCATED ABOUT 300 NM E OF THE WINDWARD ISLANDS
ALONG 55W/56W S OF 22N MOVING W 15 KT. CONVECTION IS SCANT...BUT
THERE ARE TWO SMALL CLUSTERS OF TSTMS THAT COULD BE TRACKED AS
THE WAVE AXIS. ONE CLUSTER IS ASSOCIATED WITH A SMALL SWIRL NEAR
13N57W...WHICH VERY WELL COULD BE THE WAVE. THE OTHER CLUSTER IS
ALONG THE LEADING EDGE OF THE SAHARAN AIR LAYER. EITHER
WAY...THE WAVE IS WEAK AND BEING CHOKED BY THE DRY AIR AND
SHOULD CAUSE NO PROBLEMS AS IT CROSSES THE LESSER ANTILLES
THROUGH THE NEXT 24-48 HRS. ISOLATED TSTMS FROM 12N-16N BETWEEN
54W-57W.

TROPICAL WAVE LOCATED OVER SE MEXICO AND THE BAY OF CAMPECHE
ALONG 93W S OF 22N MOVING W 10 KT. AN AREA OF UPPER LEVEL
DIFFLUENCE IS CENTERED OVER THE WAVE AND FOSTERED THE
DEVELOPMENT OF TSTMS OVER THE SW GULF OF MEXICO. THE STORMS HAVE
WEAKENED SLIGHTLY WITH WIDELY SCATTERED MODERATE CONVECTION NOW
S OF 25N BETWEEN 94W-100W.

...ITCZ...

ITCZ AXIS EXTENDS FROM SENEGAL NWWD ALONG 13N15W 16N20W...THEN
ALONG 8N23W 15N33W...THEN ALONG 10N38W 4N54W. NUMEROUS
MODERATE/STRONG CONVECTION MOVING ACROSS W GUINEA AND
GUINEA-BISSAU TOWARDS THE ATLC WATERS. SCATTERED MODERATE WITHIN
100 NM OF THE AXIS BETWEEN 19W-27W. WIDELY SCATTERED MODERATE
WITHIN 150 NM OF THE AXIS FEEDING INTO T.S. KARL. SCATTERED
MODERATE OVER PARTS OF SURINAME...GUYANA...AND E VENEZUELA.

...DISCUSSION...

GULF OF MEXICO...
IVAN IS GONE AND THE CLEANSING NWLY FLOW AND HIGH PRES BEHIND
THE SYSTEM HAS MADE FOR A PLEASANT DAY ACROSS MUCH OF THE GULF.
PWAT VALUES ESTIMATED FROM AMSU AND SSM/I HAVE DROPPED TO ABOUT
1.25" ALONG THE IMMEDIATE COAST AND IN FACT VISIBLE/INFRARED
IMAGERY INDICATES THE DRIEST AIR HAS MADE IT AS FAR S AS 27N. AN
UPPER HIGH IS CENTERED JUST E OF BROWNSVILLE TX NEAR 26N96W AND
BROAD DIFFLUENCE TO THE S HAS TRIGGERED A FEW SHOWERS/TSTMS OVER
THE FAR W GULF IN ADVANCE OF THE TROPICAL WAVE ALONG 93W. AS
THIS HIGH BUILDS NEWD ACROSS THE MIDWEST THE DRY AIR WILL BE
PUSHED EVEN FARTHER S...POSSIBLY REACHING THE N COAST OF THE
YUCATAN PENINSULA BY SUN NIGHT.

CARIBBEAN...
THE MAIN FOCUS OF WEATHER CONTINUES TO ASSOCIATED WITH RECENTLY-
DOWNGRADED TROPICAL DEPRESSION JEANNE. ALTHOUGH THE LOW-LEVEL
CENTER HAS BECOME EXPOSED...HEAVY FLOODING RAINBANDS CONTINUE TO
PLAGUE MUCH OF THE DOMINICAN REPUBLIC...PUERTO RICO...AND THE
VIRGIN ISLANDS. AN EXPANSIVE UPPER HIGH IS CENTERED JUST S OF
HISPANIOLA NEAR 17N72W AND ALTHOUGH IT HAS HELPED INCREASE THE
OUTFLOW TO THE E OF JEANNE...IT ALSO APPEARS TO BE THE CULPRIT
OF THE SWLY SHEAR THAT IS KEEPING ALL THE TSTMS TO THE E OF THE
CENTER. THE ASSOCIATED RIDGE EXTENDS TO THE SW NEAR COSTA RICA
AND THE BROAD SLY FLOW COMING OFF OF COLOMBIA IS SUPPORTING
WIDELY SCATTERED MODERATE CONVECTION OVER THE SW CARIBBEAN
WATERS FROM 9N-13N BETWEEN 76W-82W. ELSEWHERE...THE INVERTED
TROF WHICH HAS BEEN MOVING W ACROSS THE AREA IS NOW ORIENTED
FROM NICARAGUA TO JAMAICA...WITH MUCH DRIER AIR COVERING MOST OF
THE NW CARIBBEAN. DRIER AIR HAS ALSO SPREAD WWD ACROSS THE
WINDWARD ISLANDS TO THE S OF JEANNE.

SUBTROPICAL ATLANTIC....
AS UPPER RIDGING CONTINUES TO BUILD TO THE E OF T.D. IVAN...AN
EXTENSIVE FETCH OF NELY FLOW IS ADVECTING A NARROW SWATH OF
UPPER LEVEL MOISTURE OVER THE W ATLC TOWARDS THE BAHAMAS AND S
FLORIDA. A WEAKENING MID/UPPER LEVEL TROF...WHICH NOW LOOKS MORE
LIKE A SHEAR AXIS...IS JUST TO THE NW OF T.D. JEANNE ALONG
20N72W 30N65W. DRY AIR EXTENDS UP TO 300 NM NW OF THE AXIS...AND
NOW THAT JEANNE HAS BEEN DECAPITATED...THIS WILL BE THE FEATURE
IT WILL HAVE TO OVERCOME IF IT WANTS TO RE-STRENGTHEN. FARTHER
E...A WELL-DEVELOPED MID/UPPER LOW IS CENTERED NEAR 28N54W AND
IS PROPAGATING TO THE E AT ABOUT 15 KT. THERE IS A WEAK 1017 MB
LOW JUST N OF THE AREA NEAR 32N53W AND A SFC TROF EXTENDING SW
TO 26N58W. BROAD DIFFLUENCE TO THE E OF THE MID-LEVEL LOW IS
PRODUCING WIDELY SCATTERED MODERATE CONVECTION FROM 25N-32N
BETWEEN 47W-54W. TWO OTHER MID/UPPER LOWS ARE CENTERED (AND
NEARLY STATIONARY) NEAR 27N33W AND 29N18W...BUT ASIDE FROM UPPER
LEVEL CLOUDINESS NEITHER IS PRODUCING ANY SIGNIFICANT WEATHER.

TROPICAL ATLANTIC...
AN UPPER LEVEL RIDGE EXTENDS FROM THE CNTRL LESSER ANTILLES NEWD
BEYOND 20N50W...AND BUTTS UP AGAINST THE ANTICYCLONIC OUTFLOW OF
T.S. KARL E OF 42W. A NARROWING CYCLONIC SHEAR AXIS IS
SANDWICHED BETWEEN THE TWO RIDGES ALONG 20N41W 14N47W. THE LARGE
EXTENT OF THE RIDGING IS TRAPPING DRY SAHARAN AIR IN THE
LOW-LEVELS...AND HAS ALLOWED THE PLUME TO TRAVERSE MUCH OF THE
TROPICAL ATLC (IT IS NOW AS FAR W AS 55W). UPPER LEVEL RIDGING
ALSO EXTENDS E OF T.S. KARL ALONG 14N...BUT THE ACCELERATION OF
THE EQUATORWARD FLOW S OF 10N IS PRODUCING ENOUGH SPEED
DIVERGENCE TO ENHANCE CONVECTION ALONG THE ITCZ BETWEEN 20W-30W.

$$
BERG


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