[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 091053
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1015 UTC.

...SPECIAL FEATURES...

TROPICAL STORM MATTHEW IS CENTERED OVER THE W GULF OF MEXICO
NEAR 25.6N 92.9W...OR ABOUT 335 MILES SOUTHWEST OF THE MOUTH OF
THE MISSISSIPPI RIVER...AT 09/0900 UTC. MATTHEW IS MOVING NE AT
8 KT. MAXIMUM SUSTAINED WIND SPEED IS 35 KT WITH GUSTS TO 45 KT
AND THE MINIMUM CENTRAL PRESSURE IS 1002 MB. SEE LATEST NHC
FORECAST/ ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC
FOR MORE DETAILS.  MATTHEW IS EMBEDDED WITHIN STRONG SW FLOW
ALOFT ASSOCIATED WITH AN AMPLIFYING TROUGH OVER THE CENTRAL
UNITED STATES AND NW MEXICO.  THIS PATTERN CONTINUES TO CREATE
STRONG SHEAR OVER MATTHEW AND THE FIRST FEW SATELLITE IMAGES
COMING OUT OF THE ECLIPSE NOW SHOW A COMPLETELY EXPOSED LOW
LEVEL CIRCULATION. IN ADDITION...THE EARLIER IMPRESSIVE CDO
FEATURE HAS WEAKENED CONSIDERABLY WITH ONLY A FEW SMALL CELLS OF
DEEP CONVECTION OCCURRING TO THE EAST. A LARGE AREA OF
CLOUDINESS AND SHOWERS/THUNDERSTORMS CONTINUES WELL NE OF
MATTHEW OVER THE N CENTRAL GLFMEX AND GULF COAST FROM THE
FLORIDA PANHANDLE WESTWARD TO TEXAS/LOUISIANA BORDER. RADAR
IMAGERY INDICATES THE STRONGEST OF THIS ACTIVITY HAS BEEN
FOCUSED OVER SE LOUISIANA DURING THE NIGHT WITH NEW ACTIVITY IS
NOW TO THE SOUTH. GIVEN THE STEADY STREAM OF TROPICAL MOISTURE
SURGING NWD AND THE IMPROVING MID-UPPER LEVEL DYNAMICS
ASSOCIATED WITH THE AFOREMENTIONED APPROACHING TROUGH...LOCALLY
HEAVY RAIN IS LIKELY WITHIN THIS AREA OVER THE WEEKEND PRIOR TO
THE ARRIVAL OF MATTHEW LATE SUNDAY/EARLY MONDAY.  IN FACT...MANY
LOCAL NWS OFFICES HAVE ISSUED FLOOD WATCHES/WARNINGS FROM
LOUISIANA TO THE FLORIDA PANHANDLE IN ANTICIPATION OF THIS EVENT.

A 1009 MB LOW IS LOCATED APPROXIMATELY 300 NM SE OF BERMUDA NEAR
29N61W MOVING NW NEAR 10 KT. SATELLITE IMAGERY INDICATES THE LOW
IS LOCATED ALONG THE TAIL END OF A FRONTAL TROUGH OVER THE
CENTRAL SUBTROPICAL ATLC AND WITHIN 500 NM EAST OF A LARGE
MIDDLE TO UPPER LEVEL LOW SW OF BERMUDA.  GIVEN THESE
CONDITIONS...THE LOW CURRENTLY APPEARS TO BE SUBTROPICAL IN
NATURE. THE LOW LEVEL CIRCULATION HAS BECOME A BIT BETTER
DEFINED IN SATELLITE IMAGERY OVERNIGHT BUT ASSOCIATED CONVECTION
REMAINS WELL REMOVED TO THE NORTH. SCATTERED MODERATE ACTIVITY
FROM 30N-34N BETWEEN 58W-70W. NONETHELESS...SUBTROPICAL OR
TROPICAL DEVELOPMENT IS POSSIBLE WITHIN THE NEXT 36 HRS AS THE
SYSTEM MOVES TOWARD TO NW AND THE UPPER LOW DROPS SEWD.
REGARDLESS OF DEVELOPMENT...THE LOW WILL PRODUCE STRONG WINDS TO
NEAR GALE FORCE PRIMARILY TO THE NORTH OF THE LOW CENTER.

...TROPICAL WAVES...

TROPICAL WAVE LOCATED JUST W OF THE CAPE VERDE ISLANDS ALONG 29W
S OF 19N MOVING W NEAR 10 KT.  A HIGH AMPLITUDE MID-UPPER TROUGH
IS LOCATED OVER THE E ATLC AND IS PRODUCING BELLIGERENT SHEAR
OVER THE WAVE. ASSOCIATED CONVECTION HAS WEAKENED SIGNIFICANTLY
OVERNIGHT AND THE REMAINING CLOUDINESS AND ISOLATED SHOWERS HAVE
BECOME  DISPLACED WELL E OF THE WAVE AXIS.

TROPICAL WAVE LOCATED ABOUT 650 NM E OF BARBADOS ALONG 49W S OF
14N MOVING W 15-20 KT.  THE WAVE IS NEARING THE W PERIPHERY OF A
MID-UPPER LEVEL RIDGE AND ASSOCIATED CONVECTION HAS INCREASED
DURING THE NIGHT.  NUMEROUS MODERATE CONVECTION IS LOCATED FROM
8N-13N BETWEEN 50W-54W.  SIGNIFICANT DEVELOPMENT IS NOT EXPECTED
AS STRONG SW SHEAR LIES AHEAD OF THE WAVE IN ASSOCIATION WITH A
TROUGH OVER THE E CARIBBEAN.

...ITCZ...

ITCZ AXIS OFF THE COAST OF AFRICA NEAR GUINEA-BISSAU WSW ALONG
10N30W 10N45W 8N50W ILL-DEFINED TO 10N65W 8N80W. WIDELY
SCATTERED MODERATE CONVECTION FROM 6N-11N BETWEEN 25W-40W.

...DISCUSSION...

GULF OF MEXICO...
IN THE MIDDLE TO UPPER LEVELS...AN AMPLIFIED RIDGE COVERS MOST
OF THE GLFMEX WITH AXIS EXTENDING FROM THE BAY OF CAMPECHE NEWD
OVER THE FLORIDA PANHANDLE INTO THE SE UNITED STATES. THE RIDGE
IS SLIDING EWD AHEAD OF A STRONG MID-LATITUDE TROUGH PROGRESSING
THROUGH THE CENTRAL UNITED STATES FROM NW MEXICO TO THE GREAT
LAKES REGION.  THE TROUGH CONTINUES TO TRIGGER SHOWERS/TSTMS
OVER INTERIOR MEXICO PRIMARILY FROM THE ISTHMUS OF TEHUANTEPEC
WESTWARD TO MEXICO CITY.  THE UPPER TROUGH IS ALSO PRODUCING
STRONG SW SHEAR OVER T.S. MATTHEW AND STEERING THE SYSTEM IN A
GENERAL EAST-NORTHEASTWARD DIRECTION.  THIS OVERALL PATTERN IS
PUMPING COPIOUS TROPICAL MOISTURE NEWD INTO THE SE UNITED STATES
RESULTING IN CLOUDINESS AND SHOWERS/THUNDERSTORMS ALONG THE N
GULF COAST FROM LOUISIANA EWD TO THE FLORIDA PANHANDLE. GOOD
UPPER DYNAMICS/LIFT WILL LIKELY RESULT IN LOCALLY HEAVY RAINFALL
AND POSSIBLE FLOODING TODAY AND TONIGHT OVER THE NE GLFMEX AND E
GULF COAST AHEAD OF MATTHEW WHICH IS FORECAST TO APPROACH SE
LOUISIANA AND S MISSISSIPPI SUNDAY.

CARIBBEAN
LARGE MID/UPPER LEVEL TROUGH OVER THE W ATLC EXTENDS SWD INTO
THE E CARIBBEAN OVER PUERTO RICO/HISPANIOLA. A MID-UPPER LEVEL
RIDGE LIES W OF THE TROUGH EXTENDING EWD FROM S MEXICO TO
15N70W. THIS PATTERN IS PRODUCING DRY N/NW FLOW OVER MOST OF THE
CARIBBEAN W OF 70W. THE ONLY WEATHER OF NOTE W OF THE TROUGH
AXIS IS AN AREA OF SCATTERED SHOWERS/THUNDERSTORMS OVER
HISPANIOLA AND JAMAICA ALONG A LOW LEVEL CONVERGENCE LINE
EXTENDING SWD FROM A LOW CENTER OVER THE ATLC. THIS ACTIVITY HAS
BEEN SPREADING SEWD OVERNIGHT AND MAY AFFECT PUERTO RICO LATER
TODAY.  EAST OF THE TROUGH...MOIST SW FLOW AND UPPER LEVEL
DIVERGENT FLOW CONTINUES TO PRODUCE CLOUDINESS AND
SHOWERS/THUNDERSTORMS OVER THE EXTREME SE CARIBBEAN AND LESSER
ANTILLES. WHILE THE MAIN ACTIVITY HAS BEEN PRIMARILY JUST E OF
THE AREA OVERNIGHT...NEW DEVELOPMENT IS BEGINNING TO FORM OVER
THE WINDWARD/LEEWARD ISLANDS. NUMERICAL GUIDANCE INDICATES THE
UPPER TROUGH WILL REMAIN NEARLY STATIONARY KEEPING THE OVERALL
UNSETTLED/WET PATTERN OVER THE SE CARIBBEAN AND LESSER ANTILLES
DURING THE NEXT 2-3 DAYS.

SUBTROPICAL ATLANTIC...
A HIGH AMPLITUDE TROUGH-RIDGE-TROUGH PATTERN EXISTS OVER THE
SUBTROPICAL ATLC WITH A LARGE MID/UPPER LEVEL LOW CENTERED ABOUT
300 NM SW OF BERMUDA...RIDGE OVER THE CENTRAL ATLC BETWEEN
35W-60W...AND TROUGH OVER THE E ATLC FROM JUST W OF THE CANARY
ISLANDS SWD INTO THE TROPICAL ATLC NEAR 10N33W.  THE W ATLC
UPPER LOW REMAINS THE PRIMARY WEATHER MAKER WITH BROAD DIVERGENT
FLOW TO THE EAST PRODUCING A LARGE AREA OF CLOUDINESS AND
SHOWERS/THUNDERSTORMS OVER THE CENTRAL ATLC.  SCATTERED MODERATE
TO STRONG CONVECTION LIES WITHIN 175 NM EITHER SIDE OF A LINE
EXTENDING FROM TRINIDAD/TOBAGO NEWD THROUGH 20N55W TO 32N53W.
THIS UPPER LOW IS ALSO PROVIDING THE SUPPORT FOR THE FORMATION
OF A 1009 MB SUBTROPICAL LOW NEAR 29N61W DISCUSSED IN THE
SPECIAL FEATURE SECTION. SCATTERED MODERATE CONVECTION
ACCOMPANIES THE SUBTROPICAL LOW FROM 30N-34N BETWEEN 58W-70W.
STRONG SUBSIDENCE ON THE BACKSIDE OF THE UPPER LOW COVERS THE
REMAINDER OF THE W ATLC CREATING DRY/TRANQUIL CONDITIONS.
MID-UPPER LEVEL MOISTURE ASSOCIATED WITH AFOREMENTIONED
CONVECTIVE ACTIVITY RIDES UP AND OVER THE CENTRAL ATLC RIDGE
LEAVING MUCH OF THE E ATLC UNDER DRY NW FLOW.
ADDITIONALLY...MODERATE SUBSIDENCE ACCOMPANIES AN UPPER TROUGH
AXIS EXTENDING FROM 32N22W TO 10N33W.  ATTENDANT COLD FRONT
EXTENDS FROM SPAIN SWD OVER THE CANARY ISLANDS WHERE IT BECOME
DISSIPATING TO 25N30W. ONLY A FEW ISOLATED SHOWERS ACCOMPANY THE
FRONTAL BOUNDARY. ELSEWHERE AT THE SURFACE...THE SUBTROPICAL
RIDGE REMAINS LARGELY DISRUPTED BY THE 1009 MB LOW SE OF BERMUDA
CREATING A RELATIVELY WEAK PRES GRADIENT OVER THE E ATLC.  HIGH
PRES RIDGE ALONG THE E COAST OF THE UNITED STATES COUPLED WITH
AREA OF LOW SE OF BERMUDA IS PRODUCING STRONG NE TO E WINDS OVER
MUCH OF THE W ATLC.

TROPICAL ATLANTIC...
A LARGE UPPER LEVEL HIGH E OF THE LESSER ANTILLES NEAR 15N46W
COVERS THE W HALF OF THE TROPICAL ATLC WHILE A MID-UPPER LEVEL
TROUGH OVER THE E ATLC EXTENDS WELL INTO THE TROPICAL REGIONS
FROM 20N27W TO 10N33W.  THE UPPER TROUGH IS PRODUCING STRONG SW
SHEAR FROM THE CAPE VERDE ISLANDS EWD TO THE COAST OF AFRICA
WITH MODERATE SUBSIDENCE TO THE WEST PENETRATING THE ITCZ
BETWEEN 30W-40W.

$$
RHOME







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