000
AXNT20 KNHC 091807
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST SUN DEC 09 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 1745 UTC.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH PASSES THROUGH COASTAL SIERRA LEONE NEAR 
8N13W AND QUICKLY TRANSITIONS TO THE ITCZ NEAR 7N16W. THE ITCZ 
CONTINUES THROUGH 4N30W TO 6N41W WHERE IT BECOMES DIFFUSE ACROSS 
THE REMAINDER OF THE DEEP TROPICAL ATLC. SCATTERED MODERATE 
ISOLATED STRONG CONVECTION WAS NOTED FROM 3N-6N BETWEEN 20W AND 
30W...AND FROM 4N-8N BETWEEN 30W AND 38W. ADDITIONAL CLUSTERS OF 
CONVECTION WERE NOTED FROM 7N-15N BETWEEN 48W AND 56W IN 
ASSOCIATION WITH A SURFACE TROUGH AND ITS INTERACTION WITH AN
UPPER LEVEL TROUGH. 

...DISCUSSION...

THE GULF OF MEXICO...
BROAD UPPER LEVEL WEST-SOUTHWESTERLY WINDS COVERS THE GULF OF 
MEXICO AND FLORIDA ALONG THE PERIPHERY OF A LARGE UPPER LEVEL 
ANTICYCLONE OVER THE NW CARIBBEAN. DRY AIR ALOFT OVER CENTRAL 
AMERICA AND THE SW HALF OF THE GULF WAS WORKING ITS WAY NE 
ACROSS THE W-CENTRAL GULF. AT THE SURFACE...A WEAK RIDGE 
PERSISTED OVER THE GULF WITH LIGHT E TO SE WINDS OF AROUND 10 
KT E OF 90W TURNING MORE TO THE SOUTH AND INCREASING TO 15-20 KT 
OVER THE GULF N OF 28N W OF 90W WHICH EXTENDED TO THE UPPER 
TEXAS AND LOUISIANA COASTS. VISIBLE SATELLITE IMAGERY REVEALED 
MOSTLY CLEAR SKIES WITH STREETS OF LOW CLOUDS STREAMING NORTH 
OVER THE NW GULF WITHIN THE AREA OF THE STRONGEST LOW LEVEL 
FLOW. A COLD FRONT IS SLATED TO MOVE OFF THE TEXAS COAST AROUND 
12 UTC MONDAY WITH WINDS SHIFTING TO THE NORTH AND INCREASING TO 
20-25 KT LATE MON NW OF THE FRONT. 

THE CARIBBEAN SEA...
AN EXTENSIVE UPPER LEVEL ANTICYCLONE AND RIDGE COVERS THE WESTERN 
TWO-THIRDS OF THE CARIBBEAN WITH DRY AIR ALOFT IN ITS WAKE. THE 
ONLY EXCEPTION IS A PATCH OF DEEP LAYERED MOISTURE ASSOCIATED 
WITH CONVECTION OVER THE AREA FROM 16N-20N BETWEEN JAMAICA AND
82W. FURTHER EAST...A FAIRLY SHARP MID-TO UPPER LEVEL TROUGH 
EXTENDS FROM THE ATLANTIC OCEAN ACROSS THE NE LEEWARD ISLANDS TO 
A BASE OVER EXTREME NORTHERN VENEZUELA NEAR 12N70W. UPPER LEVEL
DIFLUENT FLOW WAS AIDING IN MAINTAINING SOME CONVECTION AND 
RESIDUAL MID TO UPPER LEVEL MOISTURE ACROSS THE EXTREME SE 
CARIBBEAN AND THE WINDWARD ISLANDS S OF 15N. AT THE SURFACE...
A WEAK SURFACE TROUGH IS ALONG 84W/85W FROM 14N IN EASTERN 
HONDURAS TO 20N. SCATTERED MODERATE TO STRONG CONVECTION WAS 
NOTED WITHIN 90 NM OF 18N80.5W OR CENTERED ABOUT 125 NM WSW OF 
JAMAICA. OTHER CLUSTERS OF STRONG CONVECTION WERE NOTED 
WITHIN 90 NM N OF THE COAST OF PANAMA AND WITHIN 45-60 NM OF 
13.5N67W. ELSEWHERE ACROSS THE BASIN...LOW TOPPED SHOWERS 
WERE POSSIBLE IN LOW CLOUDS STREAMING ACROSS THE CARIBBEAN.
1336 AND 1516 UTC ASCAT PASSES INDICATED AN AREA OF 20-25 KT 
WINDS FROM 12N TO 17N BETWEEN 65W AND 78W. THIS AREA WAS 
REFLECTED IN THE HIGH SEAS FORECAST...MIAHSFAT2...AND THE 
OFFSHORE WATERS FORECAST...MIAOFFNT3. 

THE ATLANTIC OCEAN...
A MID-TO UPPER LEVEL TROUGH EXTENDED THROUGH 32N38W TO 21N55W
AND INTO THE CARIBBEAN SEA VIA THE NE LEEWARD ISLANDS. BROAD 
WEST-NORTHWESTERLY FLOW SPANNED THE ATLANTIC W OF THE TROUGH AXIS
TO THE E COAST OF FLORIDA WITH SOME OF THIS FLOW ASSOCIATED WITH 
THE PERIPHERY OF A LARGE ANTICYCLONE OVER THE NW CARIBBEAN. A 
SHORTWAVE TROUGH WAS SKIRTING THE FAR NORTHERN PORTION OF THE 
AREA ALONG 70W AND IS EXPECTED TO REMAIN N OF THE AREA IN 
GENERALLY ZONAL FLOW ALOFT. 
 
AT THE SURFACE....A WEAK SURFACE TROUGH EXTENDED FROM 32N80W TO 
THE COAST OF FLORIDA NEAR CAPE CANAVERAL WHERE A 1017 MB SPOT LOW 
WAS NOTED ALONG THE TROUGH. THIS TROUGH WAS PRODUCING MAINLY LOW 
CLOUDS AND ISOLATED SHOWERS OVER THE AREA. 1027 HIGH PRESSURE N 
OF THE AREA NEAR 34N53W GOVERNED THE WEATHER OVER THE 
SUBTROPICAL ATLC N OF 20N BETWEEN 50W AND THE BAHAMAS. FURTHER 
EAST...A SURFACE TROUGH EXTENDS THROUGH 32N33W 27N37W TO 26N43W. 
A DISSIPATING STATIONARY FRONT EXTENDS FROM 32N26W TO 23N33W 
WHERE IT TRANSITIONS TO A SHEAR LINE THROUGH 18N40W TO 15N49W. A 
SURFACE RIDGE PASSES THROUGH THE MADEIRA ARCHIPELAGO TO 24N26W 
AND 16N34W. WIDELY SCATTERED MODERATE CONVECTION WITHIN BROADER 
STRATIFORM PRECIPITATION WAS POSSIBLE FROM 28N TO 32N BETWEEN 
24W AND 28W. AS NOTED ABOVE A SURFACE TROUGH IS ALONG 14N53W TO 
8N57W. CLUSTERS OF SCATTERED MODERATE CONVECTION WERE NOTED FROM 
7N-15N BETWEEN 48W AND 56W. 

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

$$
COBB