[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 041056
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT MON 04 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...
NONE.

...TROPICAL WAVES...
EASTERN MOST TROPICAL WAVE NOW EXTENDS ALONG 26N40W-18N43W-9N43W
MOVING W AT 10-15 KT. THIS WAVE HAS BROADENED AND DEEPENED OVER
THE PAST 12 HOURS SO THE WAVE AXIS APPEARS ONLY TO BE DRIFTING
WESTWARD. THIS WAVE IS ALSO OVERTAKING THE WAVE TO THE WEST.
THIS WAVE CONTINUES TO EXPERIENCE WESTERLY SHEAR WHICH
PREVENTING ORGANIZATION. SCATTERED SHOWERS/THUNDERSTORMS ARE
WITHIN 120 NM OF LINE 13N36W-20N42W.

TROPICAL WAVE APPROXIMATELY 510 NM E OF BARBADOS IS ALONG 51W S
OF 19N MOVING W 5-10 KT. THIS A SHALLOW WAVE WITH AN EMBEDDED
LOW LEVEL CIRCULATION ALONG THE WAVE NEAR 12N. THIS WAVE IS
LOCATED NEAR THE W PERIPHERY OF A MID/UPPER LEVEL RIDGE WHICH IS
PROVIDING A DIVERGENT UPPER LEVEL PATTERN AND ENHANCING
CONVECTIVE ACTIVITY. HOWEVER...WESTERLY SHEAR IS PREVENTING
ORGANIZATION. SCATTERED MODERATE/STRONG CONVECTION WITHIN 60 NM
OF LINE 15N47W-16N51W. SCATTERED SHOWERS/THUNDERSTORMS DOT THE
REMAINDER OF THE AREA FROM 11N-16N BETWEEN 42W-54W.

TROPICAL WAVE OVER THE CENTRAL CARIBBEAN IS ALONG 74W/75W S OF
20N MOVING W 10-15 KT. THE NORTHERN PORTION OF THIS IS WAVE HAS
BEEN SLOWING OVER THE PAST 12 HOURS. THE WAVE IS LOCATED WITHIN
AN AREA OF STRONG UPPER LEVEL WESTERLY FLOW AND MODERATE
SUBSIDENCE. NO ASSOCIATED SHOWERS/CONVECTION.

TROPICAL WAVE OVER S MEXICO IS ALONG 94W S OF 21N MOVING W 10-15
KT. THIS WAVE HAS BROADENED OVER THE PAST 12 HOURS SO THE WAVE
AXIS APPEARS ONLY TO BE DRIFTING WESTWARD. WAVE IS LOCATED NEAR
UNDER A MID/UPPER LEVEL LOW WHICH IS PROVIDING A DIVERGENT
UPPER LEVEL PATTERN AND ENHANCING CONVECTIVE ACTIVITY. SCATTERED
MODERATE/STRONG CONVECTION IS WITHIN 100 NM OF LINE FROM
22N90W21N95W INTO THE BAY OF CAMPECHE AND INLAND OVER MEXICO S
TO NEAR 18N97W.

...ITCZ...
ITCZ IS CENTERED ALONG 15N10W 10N20W 9N37W 13N55W 10N64W.
SCATTERED MODERATE/STRONG CONVECTION IS WITHIN 90 NM OF LINE
11N22W-9N31W. CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS FROM 2N-10N 31W-45W.

...DISCUSSION...
THE GULF OF MEXICO AND W ATLANTIC...
ZONAL WESTERLY FLOW DOMINATES MOST OF THE GULF N OF EXCEPT FOR
IN THE SW MID/UPPER LEVEL LOW/TROUGH DOMINATES THAT AREA. A
TROPICAL WAVE IS UNDER THIS LOW/TROUGH ENHANCING CONVECTION
THERE. SEE TROPICAL WAVES ABOVE. SHORTWAVE TROUGH EXTENDS OFF
THE U.S. E COAST FROM 32N75W TO THE N BAHAMAS NEAR 26N79W. THIS
IS PRODUCING SHOWERS/THUNDERSTORMS FROM 31N-32N BETWEEN 73W-78W
BUT IS OTHERWISE BENIGN. THE E GULF IS UNDER MODERATE SUBSIDENCE
PRODUCING RELATIVELY DRY CONDITIONS.

THE CARIBBEAN SEA...
MID/UPPER LEVEL LOW/TROUGH WHICH HAS RETROGRADING ACROSS CENTRAL
AMERICA INTO S MEXICO AND THE E PACIFIC. WATER VAPOR IMAGERY
INDICATES THAT THE UPPER LOW IS DEGENERATING INTO A TROUGH AXIS
NOW ALONG 91W. NOW THE FOCUS IS ON A SHARP MID/UPPER LEVEL RIDGE
EXTENDS FROM PANAMA NW TO THE SE TIP OF THE YUCATAN PENINSULA.
THE DOWNSLOPE OF THE RIDGE IS PRODUCING SCATTERED/NUMEROUS
STRONG CONVECTION S OF 10N E OF 82W INTO COLOMBIA AND PANAMA.
MID/UPPER LEVEL TROUGH OVER THE CENTRAL ATLC EXTENDS S INTO THE
E CARIBBEAN N OF 12N. THE TROUGH HAS REMAINED ESSENTIALLY
STATIONARY OVER THE LAST 24 HOURS BUT IS STARTING TO SHIFT
WESTWARD OVER THE CARIBBEAN AS THE MID/UPPER LEVEL LOW/TROUGH
MOVES OUT OF THE W CARIBBEAN. THIS IS BRINGING DRIER CONDITIONS
E OF 73W.

THE SUBTROPICAL ATLANTIC OCEAN...
THE RIDGE OVER THE W ATLC IS BLOCKING UPSTREAM DYNAMICS AND
MOISTURE KEEPING THE AREA W OF 60W UNDER MODERATE SUBSIDENCE AND
DRY/TRANQUIL CONDITIONS. IN THE CENTRAL ATLC...NEAR STATIONARY
MID/UPPER LEVEL TROUGH HAS NARROWED CONSIDERABLY OVER THE PAST
24 HOURS AND IS NOW BETWEEN 55W-62W CONTINUES TO PRODUCE
CLOUDINESS AND SCATTERED SHOWERS/THUNDERSTORMS ON THE DOWNSLOPE
SIDE OVER THE CENTRAL ATLC WITHIN 150/175 NM OF LINE FROM THE
LESSER ANTILLES NEAR 14N61W TO BEYOND 32N53W. IN THE E ATLC...
WELL DEFINED MID/UPPER LEVEL TROUGH EXTENDS FROM THE
MEDITERRANEAN SEA ACROSS NW AFRICA SW THROUGH A LARGE UPPER LOW
JUST SW OF THE CANARY ISLANDS NEAR 30N19W TO 20N33W.

THE TROPICAL ATLANTIC OCEAN...
WELL DEFINED MID/UPPER LEVEL RIDGE OVER W AFRICA EMERGES INTO
THE E ATLC JUST S OF DAKAR EXTENDING SW TO 10N45W. THE RIDGE IS
DISRUPTED W OF 45W BY THE S EXTENT OF A TROUGH OVER THE CENTRAL
ATLC. DEEP ELY FLOW COVERS THE AREA S OF THE RIDGE. HOWEVER...
THE RIDGE HAS BEEN DISPLACED FURTHER S THAN USUAL WITH STRONG
WESTERLY FLOW PENETRATING WELL INTO THE TROPICAL ATLC WATERS.
THIS PATTERN IS GENERALLY UNFAVORABLE FOR TROPICAL WAVE
DEVELOPMENT AND THE WAVES CURRENTLY MOVING ACROSS THE AREA ARE
STRONGLY SHEARED.

$$
WALLACE



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