[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 111719
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST THU DEC 11 2008

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...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1645 UTC.

...THE ITCZ...
THE ITCZ IS CENTERED ALONG 10N14W 6N23W 6N34W 7N46W 7N59W. A
SURFACE TROUGH IS EMBEDDED WITHIN THE ITCZ. THIS SURFACE TROUGH
EXTENDS FROM 13N56W TO 9N56W TO 6N56W. LOW LEVEL CONVERGENCE IS
SUPPORTING SCATTERED MODERATE CONVECTION WITHIN 210 NM E AND
60 NM W OF THIS SURFACE TROUGH. ELSEWHERE...SCATTERED MODERATE
CONVECTION IS FROM 6N-8N BETWEEN 23W-27W. SCATTERED MODERATE
CONVECTION IS ALSO FROM 7N-11N BETWEEN 45W-49W.

...DISCUSSION...

GULF OF MEXICO...
A VIGOROUS AND DEEP TROUGH...CURRENTLY IMPACTING THE E CONUS AND
GULF REGION...IS SLOWLY ADVANCING EASTWARD. AN ASSOCIATED
SURFACE COLD FRONT IS MOVING EASTWARD OVER THE E GULF...AND
EXTENDS FROM THE FLORIDA BIG BEND NEAR 30N84W TO 25N84W TO W OF
CUBA NEAR 22N85W AND EXTENDS INTO THE NW CARIBBEAN. THE
SOUTHERLY COMPONENT OF THE LOW LEVEL FLOW CONTINUES TO ADVECT
LOW LEVEL MOISTURE AHEAD OF THE COLD FRONT...WHERE ATMOSPHERIC
DESTABILIZATION IS IN PROGRESS. THE INCREASING INSTABILITY...
COMBINED WITH WITH STRONG LOW LEVEL CONVERGENCE IN THE VICINITY
OF THE COLD FRONT...IS SUPPORTING NUMEROUS SHOWERS AND
THUNDERSTORMS ALONG AND WITHIN 120 NM E OF THE COLD FRONT.
STRONG ATMOSPHERIC LIFT ASSOCIATED WITH AN UPPER LEVEL JET
MAXIMUM OVER THE N GULF AND SE CONUS IS SUPPORTING THIS SHOWER
AND THUNDERSTORM ACTIVITY...ALONG WITH THE PRESENCE OF STRONG
VERTICAL WIND SHEAR. IN THE WAKE OF THE COLD FRONT OVER THE E
GULF...A DEVELOPING SECONDARY SURFACE COLD FRONT...ALSO MOVING
EASTWARD...EXTENDS FROM THE W FLORIDA PANHANDLE NEAR 31N87W TO
26N90W TO 23N95W. WITH STABLE CONDITIONS IN WAKE OF THE COLD
FRONT OVER THE E GULF...NO DEEP CONVECTION IS OCCURRING IN THE
VICINITY OF THE DEVELOPING SECONDARY COLD FRONT. IN THE WAKE OF
THESE COLD FRONTS...INCREASED W TO NW SURFACE WINDS ARE
ADVECTING IN A MUCH COOLER AIRMASS ACROSS THE NW GULF
REGION...WITH SCATTERED STRATOCUMULUS CLOUDS ACROSS THE GULF E
OF 93W. ALSO...PRECIPITATION IS AFFECTING SE LOUISIANA AND
S MISSISSIPPI...AS WELL AS THE ADJACENT COASTAL WATERS...
ASSOCIATED WITH A DEEP LOW OVER THE SE CONUS AND A CORRESPONDING
998 MB SURFACE LOW IN CENTRAL ALABAMA NEAR 33N87W. THIS
PRECIPITATION IS FALLING IN THE FORM OF SNOW ACROSS PORTIONS OF
SE LOUISIANA AND S MISSISSIPPI...WHERE DEEP LAYER SUBFREEZING
TEMPERATURES ARE PRESENT AND WINTER STORM WARNINGS ARE IN
EFFECT. THIS RELATIVELY COOLER AIRMASS IS BEING SUPPORTED BY A
STRONG SURFACE RIDGE EXTENDING FROM N MEXICO ACROSS THE ROCKY
MOUNTAINS. THE STRONG PRESSURE GRADIENT BETWEEN THIS SURFACE
RIDGE AND THE SURFACE LOW OVER CENTRAL ALABAMA IS RESULTING IN
GALE FORCE WINDS ACROSS THE MIDDLE AND E GULF. ADDITIONALLY...
STRONG N TO NE SURFACE WINDS ARE BLOWING THROUGH THE ISTHMUS OF
TEHUANTEPEC RESULTING IN STORM FORCE WINDS IN THE E PACIFIC
REGION.

CARIBBEAN SEA...
THE SURFACE COLD FRONT OVER THE E GULF OF MEXICO EXTENDS INTO
THE NW CARIBBEAN AND IS MOVING EASTWARD. THIS COLD FRONT EXTENDS
FROM W OF CUBA NEAR 22N85W TO 20N86W TO E BELIZE NEAR 17N89W.
INSTABILITY AHEAD OF THIS FRONT...AND LOW LEVEL CONVERGENCE IN
THE VICINITY OF THIS FRONT...ARE SUPPORTING SCATTERED SHOWERS
AND THUNDERSTORMS ALONG AND WITHIN 120 NM E OF THIS FRONT. IN
THE WAKE OF THIS COLD FRONT...A RELATIVELY COOLER AIRMASS IS
PRESENT. BROAD ANTICYCLONIC FLOW ALOFT IS PRESENT AROUND AN
UPPER RIDGE THAT EXTENDS FROM NORTHERN PORTIONS OF SOUTH AMERICA
INTO THE W CARIBBEAN. MID/UPPER-LEVEL MOISTURE CONTINUES
STREAMING ACROSS THE W CARIBBEAN IN SOUTHWESTERLY FLOW ALOFT.
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE OCCURRING OVER
THE SW CARIBBEAN S OF 11N W OF 76W...WHICH ARE BEING SUPPORTED
BY LOW LEVEL CONVERGENCE IN THE VICINITY OF A 1009 MB SURFACE
LOW NW OF COLOMBIA NEAR 10N77W...AS WELL AS UPPER LEVEL
DIFFLUENCE.

ATLANTIC OCEAN...
MOIST SOUTHWESTERLY FLOW ALOFT CONTINUES TO INCREASE OVER THE
W ATLC AS THE AFOREMENTIONED DEEP TROUGH OVER THE E CONUS AND
GULF OF MEXICO CONTINUES PROGRESSING EASTWARD. AT THE SAME
TIME...THE ASSOCIATED SURFACE COLD FRONT OVER THE E GULF OF
MEXICO AND NW CARIBBEAN CONTINUES APPROACHING THE W ATLC.
SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ALONG AND AHEAD
OF THE COLD FRONT ARE FORECAST TO MOVE INTO THE W ATLC DURING
THE NEXT DAY. THE STRONG SURFACE PRESSURE GRADIENT SE OF THE
998 MB SURFACE LOW IN CENTRAL ALABAMA NEAR 33N87W IS FORECAST TO
RESULT IN GALE FORCE WINDS ACROSS PORTIONS OF THE W ATLC
BEGINNING AT 11/1800 UTC. FARTHER TO THE E...SUBSIDENCE AROUND A
1042 MB SURFACE HIGH NEAR 40N35W IS GENERALLY SUPPORTING FAIR
WEATHER CONDITIONS ACROSS MUCH OF THE CENTRAL ATLC. HOWEVER...AN
UPPER LOW IS CENTERED NEAR 28N47W...WITH ATMOSPHERIC INSTABILITY
ASSOCIATED WITH THIS UPPER LOW SUPPORTING SCATTERED SHOWERS FROM
21N-25N BETWEEN 42W-48W. ACROSS THE TROPICAL ATLC...GENERALLY
WESTERLY FLOW ALOFT IS PRESENT. ALSO...A SURFACE TROUGH...
EXTENDING FROM 13N56W TO 9N56W TO 6N56W...IS EMBEDDED WITHIN THE
ITCZ. LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED MODERATE
CONVECTION WITHIN 210 NM E AND 60 NM W OF THIS SURFACE TROUGH.

$$
COHEN




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