[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 090558
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0500 UTC.

...SPECIAL FEATURES...

TROPICAL STORM MATTHEW IS CENTERED OVER THE W GULF OF MEXICO
NEAR 24.7N 93.4W...OR ABOUT 270 MILES ESE OF BROWNSVILLE
TEXAS...AT 09/0300 UTC. MATTHEW IS MOVING ENE AT 8 KT. MAXIMUM
SUSTAINED WIND SPEED IS 40 KT WITH GUSTS TO 50 KT AND THE
MINIMUM CENTRAL PRESSURE IS 1000 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 A
SHEARED APPEARANCE IN SATELLITE IMAGERY WITH A PARTIALLY EXPOSED
LOW LEVEL CIRCULATION VISIBLE NEAR THE WEST SIDE OF THE DEEP
CONVECTION. CURRENTLY...NUMEROUS STRONG CONVECTION EXISTS WITHIN
180 NM OVER THE E SEMICIRCLE.  ADDITIONALLY...A LARGE AREA OF
CLOUDINESS AND SHOWERS/THUNDERSTORMS EXTENDS 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 IS FOCUSED NEAR SE
LOUISIANA. GIVEN THE STEADY STREAM OF TROPICAL MOISTURE SURGING
NWD AND THE IMPROVING MID-UPPER LEVEL DYNAMICS ASSOCIATED WITH
THE AFOREMENTIONED UPPER TROUGH...LOCALLY HEAVY RAIN IS POSSIBLE
WITHIN THIS AREA OVER THE WEEKEND PRIOR TO THE ARRIVAL OF
MATTHEW NEAR THE FLORIDA PANHANDLE 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 350 NM SE OF BERMUDA NEAR
28N60W DRIFTING NW. 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 AND ASSOCIATED
CONVECTION IS WELL REMOVED FROM THE LOW CENTER TO THE NORTH.
WHILE THE OVERALL APPEARANCE HAS IMPROVED SINCE THIS TIME
YESTERDAY...LATEST SATELLITE DEPICTS A BROAD LOW LEVEL CENTER
WITH MULTIPLE SWIRLS. 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 28W
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 IS WEAKENING AND BECOMING
INCREASINGLY DISPLACED E OF THE WAVE AXIS. WIDELY SCATTERED
MODERATE CONVECTION FROM 10N TO 16N BETWEEN 20W-27W INCLUDING
THE CAPE VERDE ISLANDS.

TROPICAL WAVE LOCATED ABOUT 750 NM SE OF BARBADOS ALONG 47W S OF
14N MOVING W 15-20 KT. THE WAVE IS STILL EMBEDDED PRIMARILY
WITHIN THE ITCZ. SCATTERED MODERATE CONVECTION FROM 6N-12N
BETWEEN 47W-53W. THE WAVE IS NEARING THE W PERIPHERY OF A
MID-UPPER LEVEL RIDGE WHICH IS TYPICALLY A FAVORABLE REGIME FOR
CONVECTIVE DEVELOPMENT.  BEYOND THAT...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
9N35W 10N45W 6N60W 10N80W. SCATTERED STRONG CONVECTION OVER W
AFRICA FROM 9N-14N BETWEEN 11W-18W. RAPIDLY WEAKENING AREA OF
WIDELY SCATTERED MODERATE MODERATE CONVECTION FROM 5N-11N
BETWEEN 60W-68W.

...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
EWD OVER THE CENTRAL UNITED STATES FROM NW MEXICO TO THE GREAT
LAKES REGION.  THE TROUGH CONTINUES TO TRIGGER SHOWERS/TSTMS
OVER INTERIOR MEXICO WITH THE BULK OF THE ACTIVITY FOCUSED 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.
THE 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. THE UPPER TROUGH IS EXPECTED TO
CONTINUE PROGRESSING EWD RESULTING IN UNSETTLED WEATHER
THROUGHOUT THE WEEKEND OVER THE NE GLFMEX AND E GULF COAST AHEAD
OF MATTHEW WHICH IS FORECAST TO APPROACH THE FLORIDA PANHANDLE
LATE SUNDAY/EARLY MONDAY.

CARIBBEAN
LARGE MID/UPPER 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 WINDWARD
PASSAGE.  E 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. THE MAIN ACTIVITY HAS SHIFTED JUST E OF THE ISLANDS
ALONG A LINE FROM TRINIDAD TO 20N52W.  HOWEVER...NUMERICAL
GUIDANCE INDICATES THE UPPER TROUGH WILL REMAIN NEARLY
STATIONARY KEEPING THE OVERALL PATTERN UNSETTLED/WET OVER THE
LEEWARD/WINDWARD ISLANDS 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 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 150 NM EITHER SIDE OF A LINE
EXTENDING FROM TRINIDAD/TOBAGO NEWD THROUGH 20N52W TO 31N54W.
THIS UPPER LOW IS ALSO PROVIDING THE MECHANISM FOR THE FORMATION
OF A 1009 MB SUBTROPICAL LOW NEAR 28N60W DISCUSSED IN THE
SPECIAL FEATURE SECTION. SCATTERED MODERATE CONVECTION
ACCOMPANIES THE SUBTROPICAL LOW FROM 29N-33N BETWEEN 58W-66W.
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 A TROUGH AXIS
EXTENDING FROM 32N22W TO 10N33W.  ATTENDANT COLD FRONT EXTENDS
FROM SPAIN SWD OVER THE CANARY ISLANDS WHERE IT BECOME
DISSIPATING TO 25N25W. 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 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 SUPPRESSING ITCZ CONVECTION
BETWEEN 30W-40W.

$$
RHOME






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