[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 101749
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST WED DEC 10 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
1715 UTC.

...THE ITCZ...
THE ITCZ IS CENTERED ALONG 6N9W 4N23W 7N34W 9N46W 6N58W. A
SURFACE TROUGH IS EMBEDDED WITHIN THE ITCZ. THIS SURFACE TROUGH
EXTENDS FROM 14N53W TO 11N54W TO 8N54W. LOW LEVEL CONVERGENCE IS
SUPPORTING SCATTERED MODERATE CONVECTION WITHIN 300 NM E AND 90
NM W OF THIS SURFACE TROUGH. ELSEWHERE...SCATTERED MODERATE
CONVECTION IS FROM 4N-10N BETWEEN 13W-26W. SCATTERED MODERATE
CONVECTION IS ALSO FROM 7N-9N BETWEEN 44W-47W.

...DISCUSSION...

GULF OF MEXICO...
A MAJOR CHANGE IN THE WEATHER PATTERN IS ONGOING ACROSS PORTIONS
OF THE GULF REGION...AS A VIGOROUS AND DEEP TROUGH OVER THE
CENTRAL CONUS AND N MEXICO ADVANCES EASTWARD. AN ASSOCIATED
SURFACE COLD FRONT OVER THE W GULF EXTENDS FROM S MISSISSIPPI
NEAR 30N89W TO 26N93W TO THE E COAST OF MEXICO NEAR 21N97W...AND
EXTENDS FARTHER TO THE WEST AND NORTHWEST OVER MEXICO. THIS
FRONT IS MOVING EASTWARD. AHEAD OF THE COLD FRONT...S TO SE
SURFACE WINDS OF 20 TO 30 KT CONTINUE TO ADVECT LOW LEVEL
MOISTURE ACROSS PORTIONS OF THE E AND CENTRAL GULF...WHERE
INSTABILITY CONTINUES TO INCREASE. THIS INCREASING
INSTABILITY...COMBINED WITH WITH STRONG LOW LEVEL CONVERGENCE IN
THE VICINITY OF THE COLD FRONT...IS SUPPORTING NUMEROUS STRONG
TO SEVERE THUNDERSTORMS ALONG AND WITHIN 120 NM E OF THE COLD
FRONT N OF 26N WITH A SQUALL LINE EXTENDING FROM 29N90W TO THE
W FLORIDA PANHANDLE NEAR 31N87W. AS THE AFOREMENTIONED DEEP
TROUGH CONTINUES TO APPROACH THE GULF...STRONG ATMOSPHERIC LIFT
ASSOCIATED WITH A 110 TO 120 KT UPPER LEVEL JET MAXIMUM OVER THE
THE NW GULF IS SUPPORTING THIS SHOWER AND THUNDERSTORM
ACTIVITY...ALONG WITH THE PRESENCE OF STRONG VERTICAL WIND
SHEAR. IN FACT...THE STORM PREDICTION CENTER IN NORMAN OKLAHOMA
HAS ISSUED A TORNADO WATCH FOR PORTIONS OF SOUTHERN AND EASTERN
ALABAMA...THE WESTERN AND CENTRAL FLORIDA PANHANDLE...AS WELL AS
THE ADJACENT COASTAL WATERS...EFFECTIVE UNTIL 300 PM EST THIS
AFTERNOON. OVER THE SW GULF...A 1007 MB SURFACE LOW IN THE BAY
OF CAMPECHE IS NEAR 20N41W...WITH AN ATTENDANT SURFACE TROUGH
EXTENDING FROM THE SURFACE LOW TO 23N93W TO 26N93W WHERE THE
SURFACE TROUGH INTERSECTS THE AFOREMENTIONED COLD FRONT. LOW
LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS WITHIN 60 NM
EITHER SIDE OF THE SURFACE TROUGH N OF 22N. OVER THE NEXT
DAY...THE AFOREMENTIONED SURFACE COLD FRONT IS FORECAST TO
CONTINUE MOVING EASTWARD ACROSS THE GULF REGION...WITH
CONTINUING CHANCES OF STRONG TO SEVERE THUNDERSTORMS ALONG AND
AHEAD OF THE COLD FRONT. IN THE WAKE OF THE COLD FRONT...
INCREASED NW TO N SURFACE WINDS ARE PRESENT WITH A STRONG
SURFACE PRESSURE GRADIENT...WITH GALE CONDITIONS OCCURRING
ACROSS THE NW GULF...AND STORM CONDITIONS DEVELOPING DURING THE
NEXT DAY ACROSS THE SW GULF. ALSO...A RELATIVELY COOLER AIRMASS
IS PRESENT IN THE WAKE OF THE COLD FRONT...WITH SURFACE
TEMPERATURES IN THE UPPER 30S AND LOWER 40S ACROSS PORTIONS OF
SE TEXAS AND SW LOUISIANA. THIS RELATIVELY COOLER AIRMASS IS
BEING SUPPORTED BY A 1032 MB SURFACE HIGH IN W TEXAS NEAR
32N104W. ADDITIONALLY...STRONG NW TO N SURFACE WINDS ARE
FORECAST TO BLOW THROUGH THE ISTHMUS OF TEHUANTEPEC RESULTING IN
GALE FORCE WINDS IN THE E PACIFIC REGION BEGINNING AT 11/0600
UTC.

CARIBBEAN SEA...
BROAD ANTICYCLONIC FLOW ALOFT...AROUND AN UPPER HIGH OVER
N VENEZUELA NEAR 8N70W...IS PRESENT ACROSS THE CARIBBEAN REGION.
MID/UPPER-LEVEL MOISTURE CONTINUES STREAMING ACROSS THE W GULF
IN SOUTHWESTERLY AND WESTERLY FLOW ALOFT W AND N OF THE UPPER
HIGH. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE OCCURRING
OVER THE SW CARIBBEAN S OF 11N W OF 75W...WHICH ARE BEING
SUPPORTED BY LOW LEVEL CONVERGENCE IN THE VICINITY OF A 1009 MB
SURFACE LOW IN N COLOMBIA NEAR 11N75W...AS WELL AS UPPER LEVEL
DIVERGENCE TO THE W OF UPPER HIGH OVER N VENEZUELA. OVER THE SE
CARIBBEAN...DEEP LAYER DRY AIR IS INHIBITING DEEP CONVECTION.
ACROSS THE CARIBBEAN...GENERALLY NE TO E SURFACE WINDS OF 20 TO
25 KT PREVAIL. DURING THE NEXT DAY...THE COLD FRONT OVER THE
GULF OF MEXICO WILL CONTINUE TO APPROACH THE NW GULF...WITH A
RELATIVELY COOLER AIRMASS IN THE WAKE OF THE COLD FRONT.

ATLANTIC OCEAN...
MOIST SOUTHWESTERLY FLOW ALOFT CONTINUES TO INCREASE OVER THE W
ATLC AS THE AFOREMENTIONED DEEP TROUGH OVER THE CENTRAL CONUS
AND N MEXICO CONTINUES PROGRESSING EASTWARD. DURING THE NEXT
DAY...THE COLD FRONT OVER THE GULF OF MEXICO WILL CONTINUE TO
APPROACH THE W ATLC. FARTHER TO THE E...A SURFACE STATIONARY
FRONT EXTENDS FROM 29N59W TO 30N45W TO 32N41W...WITH LOW LEVEL
CONVERGENCE SUPPORTING SCATTERED SHOWERS WITHIN 90 NM EITHER
SIDE OF THE STATIONARY FRONT E OF 50W. N OF THIS STATIONARY
FRONT...SUBSIDENCE AROUND A 1044 MB SURFACE HIGH NEAR 41N46W IS
GENERALLY SUPPORTING FAIR WEATHER. ALSO...ATMOSPHERIC LIFT AND
INSTABILITY IN THE VICINITY OF AN UPPER TROUGH N OF 24N BETWEEN
24W-34W ARE SUPPORTING SCATTERED SHOWERS FROM 24N-29N BETWEEN
24W-32W. ACROSS THE TROPICAL ATLC...GENERALLY WESTERLY FLOW
ALOFT IS PRESENT. ALSO...A SURFACE TROUGH EMBEDDED WITHIN THE
ITCZ EXTENDS FROM 14N53W TO 11N54W TO 8N54W...WITH SCATTERED
MODERATE CONVECTION WITHIN 300 NM E AND 90 NM W OF THIS SURFACE
TROUGH.

$$
COHEN


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