[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 212352
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU 21 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.

...TROPICAL WAVES...
CENTRAL ATLANTIC TROPICAL WAVE ALONG 58W SOUTH OF 18N MOVING
WEST 15 KT. THE WAVE IS CURRENTLY ENCOUNTERING MODERATE WLY
SHEAR AND MIDDLE TO UPPER LEVEL SUBSIDENCE. THIS UNFAVORABLE
ENVIRONMENT IS DISPLACING ISOLATED MODERATE CONVECTION TO THE
EAST FROM 16N-20N BETWEEN 45W-52W AND LIMITING DEVELOPMENT.
HOWEVER...THE WAVE AND ASSOCIATED MOISTURE WILL ENCOUNTER A MORE
DIVERGENT UPPER LEVEL PATTERN AS IT MOVES INTO THE E CARIBBEAN
WHICH SHOULD ALLOW FOR MORE CONVECTION.

WESTERN CARIBBEAN SEA TROPICAL WAVE ALONG 81W SOUTH OF 20N
MOVING WEST 10 KT.  THE WAVE IS NEARING THE BASE OF A LARGE
MIDDLE TO UPPER LEVEL TROUGH STRETCHING ACROSS THE CENTRAL
CARIBBEAN.  RESULTING STRONG SW FLOW IS SHEARING ASSOCIATED
CONVECTION AND RESTRICTING DEVELOPMENT.  SCATTERED
MODERATE/ISOLATE STRONG CONVECTION OVER THE SW CARIBBEAN AND
PORTIONS OF COSTA RICA/PANAMA S OF 12N BETWEEN 74W-80W.

...ITCZ...
ITCZ AXIS IS ALONG 15N10W 13N17W 7N25W 12N40W 16N50W 17N60W
11N80W 10N85W.  SCATTERED MODERATE TO STRONG CONVECTION IS OVER
THE LEEWARD ISLANDS FROM 14N-20N BETWEEN 58W-66W.  WIDELY
SCATTERED MODERATE CONVECTION IS OVER THE SW CARIBBEAN FROM
11N-14N BETWEEN 76W-80W.

...DISCUSSION...

GULF OF MEXICO AND W ATLANTIC...
1017 MB HIGH IS OVER THE CENTRAL GULF OF MEXICO. MOSTLY FAIR
WEATHER IS NOTED OVER THE ENTIRE GULF. A WEAK COLD FRONT IS OVER
THE W ATLANTIC AND N FLORIDA ALONG 32N71W 29N80W 31N87W.  A
PREFRONTAL TROUGH IS OVER THE W ATLANTIC ALONG 30N72W 27N76W
25N80W.  NO SIGNIFICANT CONVECTION IS NOTED WITH THE FRONT OR
TROUGH. THE COLD FRONT WILL CONTINUE TO PENETRATE THE W ATLC
DURING THE NEXT 24-36 HOURS AS THE SUPPORTING MIDDLE TO UPPER
LEVEL TROUGH AMPLIFIES. IN THE UPPER LEVELS... MIDDLE TO UPPER
LEVEL SHORTWAVE TROUGH WHICH MOVED OVER FLORIDA LAST NIGHT IS
NOW E OF THE AREA ALONG WITH ITS ASSOCIATED CLOUDS/CONVECTION.
THE GLFMEX IS NOW PRIMARILY DOMINATED BY A WELL-DEFINED
ANTICYCLONE ALONG THE COAST OF MEXICO NEAR TAMPICO WITH DRY NW
FLOW AND MODERATE SUBSIDENCE OVER THE ENTIRE AREA. THIS PATTERN
SHOULD KEEP THE BULK OF THE AREA UNDER A DRY/TRANQUIL WEATHER
PATTERN DURING THE NEXT FEW DAYS AS THE RIDGE AMPLIFIES NWD INTO
THE CENTRAL AND E UNITED STATES EFFECTIVELY BLOCKING UPSTREAM
DISTURBANCES FROM ENTERING THE AREA.

CARIBBEAN SEA...
THE PRIMARY FEATURE OVER THE CARIBBEAN CONTINUES TO A HIGH
AMPLITUDE MIDDLE TO UPPER LEVEL TROUGH STRETCHING FROM THE W
ATLC WATERS OVER CUBA AND HISPANIOLA TO THE SW CARIBBEAN NEAR
THE COAST OF NICARAGUA/COSTA RICA.  AS HAS BEEN THE CASE FOR THE
LAST FEW DAYS...DRY NLY FLOW IN THE MIDDLE TO UPPER LEVELS
DOMINATES THE CARIBBEAN WEST OF THE TROUGH WHILE MOIST SLY FLOW
KEEPS THE AREA E OF THE TROUGH UNSETTLED AND WET. SATELLITE
IMAGERY INDICATES SEVERAL AREAS ACTIVE CONVECTION OVER N
PORTIONS OF S AMERICA IN ASSOCIATION WITH THE ITCZ.  A SECOND
AREA OF SCATTERED CONVECTION IS LOCATED OVER THE NE CARIBBEAN
ALONG A LOW LEVEL REFLECTION OF AN UPPER TROUGH FROM THE MONA
PASSAGE TO LAKE MARACAIBO IN NW COLOMBIA.  A 50 KT SW JET FLANKS
THE E SIDE OF THE UPPER TROUGH OVER HISPANIOLA WHICH IS FOCUSING
THE BULK OF THE ACTIVITY ALONG THE N EXTENT OF THE LOW LEVEL
TROUGH...N OF 15N BETWEEN 62W-68W... OR IN THE VICINITY OF
PUERTO RICO/VIRGIN ISLANDS AND N PORTIONS OF THE LEEWARD
ISLANDS.  LATEST SATELLITE IMAGERY INDICATES NEW DEVELOPMENT S
OF THE ISLANDS WHICH IS TRAINING NWD AND AND WILL PRODUCE
LOCALLY HEAVY RAINFALL AND POSSIBLE FLOODING TODAY AND TONIGHT.
LOOKING UPSTREAM...A POTENT MIDDLE TO UPPER LEVEL SHORTWAVE
TROUGH DROPPING SEWD OVER THE BAHAMAS AND W CUBA WILL REINFORCE
THE LARGER SCALE TROUGH DURING THE NEXT 24 HOURS WITH LITTLE
OVERALL CHANGE IN THE UPPER PATTERN.  AS THE SAME TIME...A
TROPICAL WAVE WILL BE ENTERING THE E CARIBBEAN TONIGHT AND
TOMORROW BRING INCREASING LOWER LEVEL MOISTURE.  THIS EVOLUTION
SHOULD KEEP MUCH OF THE E HALF OF THE CARIBBEAN UNDER A
WET/STORMY SCENARIO DURING THE NEXT FEW DAYS.  MEANWHILE...MOST
OF THE NW CARIBBEAN WILL REMAIN UNDER DRY NLY FLOW.

SUBTROPICAL ATLANTIC...
A SURFACE 1020 MB HIGH IS OVER THE CENTRAL ATLANTIC NEAR 27N40W.
HIGH PRESSURE DOMINATES THE ATLANTIC N OF 20N BETWEEN 20W-70W.
IN THE UPPER LEVELS... AMPLIFYING MIDDLE TO UPPER LEVEL
TROUGH-RIDGE-TROUGH PATTERN PREVAILS OVER THE SUBTROPICAL ATLC
WITH A LARGE TROUGH OVER THE W ATLC BETWEEN 65W AND THE SE COAST
OF THE UNITED STATES...BROAD RIDGE OVER THE CENTRAL ATLC BETWEEN
20W-65W...AND TROUGH OVER THE E ATLC NEARING THE CANARY
ISLANDS.  THE W ATLC TROUGH IS THE PRIMARY WEATHER PRODUCER WITH
LARGE SCALE LIFT AND COPIOUS TROPICAL MOISTURE COMING TOGETHER
TO PRODUCE AN IMPRESSIVE AREA OF SCATTERED MODERATE TO STRONG
CONVECTION S OF 20N BETWEEN 58W-66W.  ISOLATED MODERATE
CONVECTION IS ALSO LOCATED NE OF THE BAHAMAS N OF 24N BETWEEN
69W-73W.  A MIDDLE TO UPPER LEVEL SHORTWAVE TROUGH IS CURRENTLY
DROPPING INTO THE W SIDE OF LARGER SCALE TROUGH RESULTING IN AN
AMPLIFICATION OF PATTERN. THIS SHOULD KEEP MUCH OF THE CENTRAL
ATLC UNDER A CLOUDY/STORMY PATTERN DURING THE NEXT FEW DAYS.
BEST LIFT/DYNAMICS WILL BE FOCUSED PRIMARILY BETWEEN 45W-65W.
ELSEWHERE...EXTENSIVE HIGH CLOUDINESS FROM W ATLC CONVECTION IS
STREAMING NEWD AND COVERS A GOOD PORTION OF THE CENTRAL TO E
ATLC.  OVER THE FAR E ATLC...MIDDLE TO UPPER LEVEL TROUGH IS
APPROACHING THE CANARY ISLANDS BUT MOST OF THE SIGNIFICANT
WEATHER WITH THIS FEATURE IS N OF THE AREA.

TROPICAL ATLANTIC...
LARGE MIDDLE TO UPPER LEVEL ANTICYCLONE NEAR 14N37W DOMINATES
MOST OF THE TROPICAL ATLC E OF 50W. DIVERGENT UPPER LEVEL FLOW
OVER THE EQUATOR WIDE SIDE OF THE ANTICYCLONE IS ENHANCING ITCZ
CONVECTION BETWEEN 30W-55W. ELSEWHERE...A WEAK SHORTWAVE TROUGH
IS LOCATED ALONG 52W BUT IS NOT PRODUCING ANY SIGNIFICANT
WEATHER.

$$
FORMOSA





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