[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 212338
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST WED NOV 21 2012

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF
SOUTH AMERICA...AND ATLANTIC 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.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS ACROSS WEST AFRICA TO THE COAST OF
GUINEA AT 10N14W TO 7N18W. THE ITCZ BEGINS AT 7N18W AND
CONTINUES ALONG 4N27W 4N39W 6N47W. A SURFACE TROUGH IS EMBEDDED
WITHIN THE ITCZ ALONG 12N47W TO 6N47W. SCATTERED MODERATE/STRONG
CONVECTION IS FROM 4N-7N BETWEEN 14W-17W. WIDELY ISOLATED
MODERATE CONVECTION IS NORTH OF THE ITCZ AXIS FROM 6N-11N
BETWEEN 24W-42W. MOST OF THIS ACTIVITY IS ENHANCED BY DIFFLUENCE
ALOFT AROUND AN UPPER LEVEL TROUGH WITH AXIS FROM 21N34W TO
7N48W.

...DISCUSSION...

GULF OF MEXICO...
MAINLY ZONAL WESTERLY FLOW COVERS THE GULF OF MEXICO ALONG WITH
DRY AIR WHICH IS HELPING PROVIDE FAIR CONDITIONS ACROSS THE
MAJORITY OF THE BASIN. A SHORTWAVE UPPER TROUGH SINKS SLIGHTLY
INTO THE NE CORNER OF THE GULF DRAWING ANOTHER SURGE OF COOL AND
DRY AIR SOUTHWARD. AT THE SURFACE...RIDGING CONTINUES ACROSS THE
BASIN WITH AXIS EXTENDING FROM A HIGH CENTER OVER ARKANSAS TO A
SECOND HIGH CENTER OVER EASTERN MEXICO NEAR 24N99W. THIS PATTERN
IS PROVIDING MAINLY NORTH TO NORTHEAST WINDS ACROSS THE BASIN
RANGING FROM 10-20 KT. A FEW ISOLATED SHOWERS ARE IN THE FAR SW
GULF NEAR A SURFACE TROUGH ALONG 23N97W TO 19N95W WHICH IS
REALLY DEPICTING AN AREA OF CONVERGENCE. SURFACE RIDGING IS
EXPECTED TO REMAIN ACROSS THE BASIN FOR THE NEXT SEVERAL DAYS.

CARIBBEAN SEA...
A BROAD UPPER LEVEL RIDGE COVERS THE CARIBBEAN WITH MAINLY DRY
WESTERLY FLOW OVER THE NW CORNER AND THE EASTERN PORTIONS WHILE
MOIST SOUTHWESTERLY FLOW COVERS THE CENTRAL CARIBBEAN. THE
COMBINATION OF MOIST SOUTHWESTERLY FLOW ALOFT AND NORTHEASTERLY
SURFACE WINDS EXPERIENCING SPEED CONVERGENCE AT THE SURFACE IS
HELPING ENHANCE SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ACROSS
THE SW CARIBBEAN SOUTH OF 13N BETWEEN 73W-84W COVERING MUCH OF
COSTA RICA AND PANAMA. THE MONSOON TROUGH ACROSS BOTH COUNTRIES
MAY ALSO BE PLAYING A ROLE IN THE ACTIVITY PROVIDING STRONGER
SURFACE CONFLUENCE IN THAT AREA. A FEW WIDELY ISOLATED SHOWERS
CONTINUE TO THE NORTH WITH ACTIVITY PRESENT OVER JAMAICA AND
HISPANIOLA. A WEAK SURFACE TROUGH IS ANALYZED IN THE EASTERN
CARIBBEAN FROM THE VIRGIN ISLANDS TO NEAR 13N70W. ISOLATED
SHOWERS ARE WITHIN 60 NM EITHER SIDE OF THE AXIS. LITTLE CHANGE
IS EXPECTED OVER THE NEXT SEVERAL DAYS.

ATLANTIC OCEAN...
A NARROW UPPER LEVEL TROUGH EXTENDS DOWN THE EASTERN SEABOARD
INTO NORTHERN FLORIDA SUPPORTING A SLIGHTLY COMPLICATED PATTERN
AT THE SURFACE OVER THE SW NORTH ATLC. A 1007 MB SPOT SURFACE
LOW IS CENTERED NEAR 27N71W WITH A SURFACE TROUGH EXTENDING FROM
THE CENTER TO NEAR 24N72W. A SECOND SURFACE TROUGH IS NORTH OF
THIS AREA EXTENDING FROM A SECOND SURFACE LOW TO THE NE NEAR
34N57W. THIS SECOND SURFACE TROUGH ENTERS THE DISCUSSION AREA
NEAR 31N62W CONTINUING ALONG 30N70W 28N78W. SCATTERED SHOWERS
ARE NORTH OF THE AXIS BETWEEN 67W-78W. ONLY A FEW WIDELY
ISOLATED SHOWERS ARE ELSEWHERE DUE TO THE PRESENCE OF STRONG DRY
AIR ALONG IN MAINLY ZONAL WESTERLY FLOW. A SECOND SHORTWAVE
UPPER TROUGH IS MOVING INTO THE CENTRAL ATLC ALONG 35N49W TO
25N45W SUPPORTING A COLD FRONT THAT ENTERS THE AREA NEAR 32N50W
TO 20N65W. ONLY A FEW ISOLATED SHOWERS ARE ALONG THE FRONTAL
BOUNDARY. MORE SCATTERED ACTIVITY IS FARTHER EAST NEAR THE AREA
OF DIFFLUENCE ALOFT AROUND THE UPPER TROUGH AXIS. ANOTHER UPPER
TROUGH AXIS IS OVER THE TROPICAL EAST ATLC ALONG 21N34W TO 7N48W
PROVIDING A LARGE AREA OF DIFFLUENCE ALOFT ACROSS THIS AREA. IT
IS HELPING SUPPORT CONVECTION NEAR AND NORTH OF THE ITCZ AXIS AS
WELL AS SOME ISOLATED SHOWERS FARTHER NORTH FROM 11N-18N BETWEEN
23W-38W. AN UPPER LEVEL RIDGE ACROSS THE NE ATLC SUPPORTS A 1025
MB HIGH NEAR 35N21W WHICH IS PROVIDING SURFACE RIDGING ACROSS
THE EASTERN ATLC PROVIDING FAIR WEATHER BESIDES NEAR WHERE THE
UPPER TROUGH IS CAUSING SOME SHOWER ACTIVITY.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

$$
WALTON





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