[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 092335
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SAT 09 OCT 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 STORM MATTHEW...RE-UPGRADED FROM TROPICAL DEPRESSION
STATUS...IS CENTERED NEAR 27.2N 91.3W...OR ABOUT 190 MILES SW OF
THE MOUTH OF MISSISSIPPI RIVER...AT 10/0000 UTC MOVING E 8 KT.
MAXIMUM SUSTAINED WIND SPEED IS 35 KT WITH GUSTS TO 45 KT.
MINIMUM CENTRAL PRESSURE REPORTED BY AN AIR FORCE RECONNAISSANCE
AIRCRAFT IS 998 MB. SEE LATEST NHC PUBLIC ADVISORY UNDER
AWIPS/WMO HEADERS MIATCPAT4/WTNT34 KNHC OR NHC FORECAST/ADVISORY
UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS.
AN AIR FORCE RECONNAISSANCE AIRCRAFT FLEW INTO MATTHEW EARLIER
THIS AFTERNOON AND FOUND THAT AS THE CONVECTION REDEVELOPED OVER
THE CENTER...THE WINDS INCREASED AGAIN TO TROPICAL STORM FORCE.
HOWEVER...THE LATEST SATELLITE IMAGES NOW SHOW THE CENTER
BECOMING EXPOSED AGAIN TO THE W OF THE STRONGEST TSTMS. MATTHEW
CONTINUES TO DISPLAY A HYBRID STRUCTURE WITH A SFC TROF BOUNDING
THE SYSTEM TO THE W FROM THE TEXAS/LOUISIANA BORDER SWD INTO THE
BAY OF CAMPECHE. DRIER AIR FROM THE SOUTHERN PLAINS IS NOW
MOVING OFF THE TEXAS COAST INTO THE W GULF...AND IT IS HIGHLY
POSSIBLE THAT MATTHEW COULD DEVELOP A TRAILING FRONTAL BOUNDARY
AS IT MOVES INLAND OVER LOUISIANA. REGARDLESS...VERY HEAVY
RAINFALL IS LOCATED TO THE E OF THE CENTER...WITH NUMEROUS
MODERATE CONVECTION FROM 25N-30N BETWEEN 87W-92W. WIDELY
SCATTERED MODERATE IS ALSO FROM 20N-25N BETWEEN 90W-96W. RADAR
IMAGERY SHOWS HEAVY RAINFALL MOVING ONSHORE THE GULF COAST
BETWEEN BATON ROUGE LOUISIANA AND PANAMA CITY FLORIDA...AND
MODEL GUIDANCE SUGGESTS THAT THIS SWATH OF HEAVY RAIN WILL MOVE
EWD TO FLORIDA OVER THE NEXT 2 DAYS EVEN AS THE CENTER OF
MATTHEW MOVES INTO THE LOWER MISSISSIPPI VALLEY.

A DEEPENING 1005 MB LOW IS CENTERED ABOUT 135 NM SSE OF BERMUDA
NEAR 30N64W WITH A SFC TROF EXTENDING EWD TO 31N57W 28N53W...AND
A SECOND DETACHED TROF FARTHER S ALONG 27N59W 22N69W. THE LOW
HAS SOME SUBTROPICAL CHARACTERISTICS BUT IT IS LACKING THE RIGHT
UPPER LEVEL STRUCTURE TO BE DEEMED SO AT THIS TIME. THE SFC
CIRCULATION IS OFFSET TO THE NE OF THE ASSOCIATED UPPER
LOW...PUTTING IT IN THE DIVERGENT SIDE OF THE UPPER TROF.
NUMEROUS MODERATE CONVECTION IS ALIGNED ALONG A BAND TO THE N OF
THE LOW FROM 31N-35N BETWEEN 60W-67W AND IS CURRENTLY MOVING
ACROSS BERMUDA WITH VERY HEAVY RAINFALL AND GALE FORCE WINDS.
CONDITIONS SHOULD BEGIN TO IMPROVE DURING THE NIGHT BUT THEN A
SECOND ROUND OF HEAVY RAIN COULD MOVE BACK ACROSS THE ISLAND
LATE TOMORROW AS THE UPPER TROF SHIFTS E. THERE IS STILL THE
POTENTIAL FOR SUBTROPICAL OR TROPICAL DEVELOPMENT OF THE SYSTEM
WITHIN THE NEXT 36 HRS...BUT IF A FRONTAL STRUCTURE BEGINS TO
DEVELOP AS IT MOVES N THEN IT WOULD BE CLASSIFIED AS A
BAROCLINIC EXTRATROPICAL CYCLONE.

...TROPICAL WAVES...

TROPICAL WAVE LOCATED 250 NM W OF THE CAPE VERDE ISLANDS ALONG
30W S OF 20N MOVING W 10 KT. SATELLITE IMAGERY HAS REVEALED A
WELL-DEFINED LOW-LEVEL CIRCULATION BUT ALL OF THE CONVECTIVE
ACTIVITY IS DISPLACED TO THE NE OF THE STRONGEST ROTATION.
SCATTERED MODERATE CONVECTION FROM 13N-17N BETWEEN 25W-30W.

TROPICAL WAVE LOCATED N OF FRENCH GUIANA ALONG 4N53W 17N50W
MOVING NW 15-20 KT. THE WAVE IS NOW MOVING IN A MORE NWLY
DIRECTION IN RESPONSE TO THE BROAD AREA OF LOW PRES OVER THE E
CARIBBEAN AND W/CNTRL ATLC. THIS HAS ALSO HELPED TO BULGE THE
ITCZ NWD WHICH IS ENHANCING TSTMS NEAR THE WAVE AXIS. SCATTERED
MODERATE CONVECTION FROM 12N-17N BETWEEN 51W-54W. ADDITIONAL
TSTMS ARE LOCATED N AND W OF THE WAVE CLOSER TO THE LESSER
ANTILLES...BUT THESE ARE DUE TO STRONG LOW-LEVEL SPEED
CONVERGENCE WHERE THE TRADE WINDS INTERSECT THE AREA OF LOW
PRES.

...ITCZ...

ITCZ AXIS IS ALONG 6N10W 6N25W...THEN ALONG 10N31W 12N47W...THEN
ALONG 8N66W TO A 1008 MB LOW OFF THE COAST OF COSTA RICA NEAR
11N82W. ISOLATED SHOWERS/TSTMS WITHIN 120 NM OF THE AXIS BETWEEN
10W-16W. ISOLATED SHOWERS/TSTMS WITHIN 180 NM S OF THE AXIS
BETWEEN 37W-45W. WIDELY SCATTERED MODERATE CONVECTION OVER
COASTAL AREAS OF VENEZUELA AND COLOMBIA.

...DISCUSSION...

GULF OF MEXICO...
A DEEP AND NEARLY STATIONARY MID/UPPER LOW IS CENTERED ALONG THE
TEXAS/NEW MEXICO BORDER AND CONTINUES TO PUMP VERY MOIST AIR
FROM THE GULF OF MEXICO NWD INTO THE SE UNITED STATES. A TILTED
UPPER TROF EXTENDS FROM THE BAY OF CAMPECHE ACROSS T.S. MATTHEW
TO THE MID-ATLC STATES WITH SLIGHTLY DIFFLUENT FLOW CENTERED
OVER THE GULF WATERS. REFER TO THE SPECIAL FEATURES SECTION FOR
DISCUSSION ON T.S. MATTHEW AND ASSOCIATED CONVECTION.

CARIBBEAN...
THE TRADE WIND FLOW ACROSS THE CARIBBEAN REMAINS WEAK DUE TO
T.S. MATTHEW OVER THE GULF OF MEXICO AND BROAD LOW PRES OVER THE
E CARIBBEAN AND W/CNTRL ATLC. THE UPPER FLOW HAS NOT CHANGED
SINCE YESTERDAY...WITH A TROF EXTENDING FROM THE MONA PASSAGE
SWD TO ARUBA AND A BROAD ANTICYCLONE LOCATED NEAR THE ISTHMUS OF
TEHUANTEPEC. THIS PATTERN CONTINUES TO PUMP MOSTLY DRY AIR OVER
THE W/CNTRL CARIBBEAN AND TROPICAL MOISTURE NWD OVER THE LESSER
ANTILLES. A WEAK SFC TROF EXTENDS FROM THE N LEEWARD ISLANDS SW
TO 13N66W AND STRONG LOW-LEVEL CONVERGENCE TO THE E OF THIS AXIS
IS SUPPORTING SCATTERED MODERATE CONVECTION FROM 14N-19N BETWEEN
57W-62W INCLUDING THE ISLANDS OF MARTINIQUE...DOMINICA...AND
GUADELOUPE. OTHER TSTMS HAVE ALSO POPPED OVER THE TERRAIN OF
JAMAICA...HISPANIOLA...AND PUERTO RICO.

SUBTROPICAL ATLANTIC...
A DEEP-LAYERED TROF COVERS MUCH OF THE W ATLC WITH WATER VAPOR
IMAGERY AND CIMSS SATELLITE-DERIVED WIND VECTORS INDICATING A
MID-LEVEL LOW CENTERED SW OF BERMUDA NEAR 27N70W. DRY AIR IS
SPIRALING INTO THE BASE OF THE TROF ACROSS THE BAHAMAS AND IS
THEN CREATING A DRY SLOT-LIKE FEATURE THAT WILL SOON SPREAD
ACROSS BERMUDA. REFER TO THE SPECIAL FEATURES SECTION FOR
SPECIFICS ON THE SFC LOW PRES NEAR THE ISLAND. FARTHER
E...LOW-LEVEL SPEED CONVERGENCE COVERS THE CNTRL ATLC WITH
SCATTERED MODERATE CONVECTION DEVELOPING FROM 22N-32N BETWEEN
50W-55W. AN UPPER LEVEL RIDGE EXTENDS ALONG 50W WITH BROAD NWLY
FLOW FEEDING INTO A NARROWING UPPER TROF WHICH NOW EXTENDS FROM
PORTUGAL SWWD ACROSS THE CANARY ISLANDS TO 20N25W. A DISSIPATING
COLD FRONT HAS BEEN HELPED ALONG BY THE TROF AND EXTENDS FROM N
MOROCCO THEN TO THE S OF THE CANARY ISLANDS BUT THERE IS VERY
LITTLE ACTIVE WEATHER EXCEPT FOR INCREASED MID/HIGH LEVEL
CLOUDINESS SE OF THE FRONT.

TROPICAL ATLANTIC...
A LARGE UPPER LEVEL ANTICYCLONE IS CENTERED E OF THE LESSER
ANTILLES NEAR 15N51W AND IS HELPING TO FEED LARGE AMOUNTS OF
TROPICAL MOISTURE NWD INTO THE SUBTROPICS. ON THE OTHER
SIDE...DRY AIR IS BEING PULLED SWD INTO THE TROPICS WITH VERY
LITTLE CLOUDINESS OBSERVED N OF THE ITCZ BETWEEN 30W-45W. WEAK
UPPER LEVEL TROUGHING EXTENDS INTO THE AREA FROM THE CANARY
ISLANDS TO THE CAPE VERDE ISLANDS AND IS SPREADING MOISTURE NEWD
ACROSS MOST OF W AFRICA. THIS IS ALLOWING CONVECTION TO FIRE
NEAR THE TROPICAL WAVE ALONG 30W BUT THE WLY SHEAR IS KEEPING
THE ACTIVITY E OF THE WAVE AXIS.

$$
BERG


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