000
AXNT20 KNHC 162359
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL  
705 PM EST WED DEC 16 2009

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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2200 UTC.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 7N12W 5N22W 6N40W 1N50W.  
SCATTERED MODERATE CONVECTION IS WITHIN 30 NM EITHER SIDE OF THE 
ITCZ AXIS BETWEEN 21W AND 24W AS WELL AS FROM 06N TO 12N BETWEEN 
26W AND 33W.

...DISCUSSION...

GULF OF MEXICO...
A 1016 MB LOW PRES CENTER NEAR 25N96W WILL SLOWLY DEEPEN AND 
LIFT NORTHEASTWARD OVER THE NEXT 24 HOURS...REMAINING IN THE 
GULF OF MEXICO UNTIL THE UPPER LEVEL LOW CURRENTLY OVER TEXAS 
FINALLY REACHES THE SURFACE SYSTEM. THE DEEP LAYERED SYSTEM WILL 
THEN BE PROPELLED EASTWARD INTO NORTHERN FLORIDA/SOUTHERN 
GEORGIA BY FRI AFTERNOON AS THE UPPER LOW DISSIPATES AND MOVES 
INTO THE LEADING EDGE OF THE NORTHERN STREAM TROUGH AMPLIFYING 
OVER THE PLAINS AND MISSISSIPPI VALLEY. THE SURFACE LOW WILL 
DEEPEN RAPIDLY ON FRI AS THE DEEP LAYER SYSTEM MOVES INTO THIS 
AMPLIFIED TROUGH. THE 1800 UTC SURFACE ANALYSIS SHOWS A TIGHT 
PRES GRADIENT BETWEEN THE DEVELOPING LOW PRES AND A 1034 MB HIGH 
PRES CENTER OVER NORTHERN MEXICO NEAR 27N102W AS WELL AS A 1036 
MB HIGH PRES CENTER NEAR 38N88W. AS A RESULT...A GALE WARNING IS 
IN EFFECT FOR THE NW GULF OF MEXICO. GALE FORCE WINDS ARE 
EXPECTED SPREAD EASTWARD INTO THE CENTRAL GULF THROUGH THU AS 
THE SYSTEM INCHES EASTWARD. GALE FORCE WINDS ARE FORECAST TO 
DIMINISH BEFORE SUNRISE FRI AS THE HIGH PRES NORTH OF THE LOW 
MIGRATES NORTHWARD INTO CANADA...DECREASING THE PRES GRADIENT. 
RADAR SHOWS WIDESPREAD MODERATE TO HEAVY RAIN OVER SOUTH TEXAS 
AND A DEVELOPING BAND OF SHOWERS AND THUNDERSTORMS ACROSS SOUTH 
FLORIDA ALONG THE STATIONARY FRONT EXTENDING FROM THE LOW. THE 
SYSTEM WILL CONTINUE TO BRING WIDESPREAD PRECIPITATION TO THE 
GULF...THE GULF COAST...AND FL THROUGH THE FORECAST PERIOD.

CARIBBEAN SEA...
FRESH EASTERLY TRADES PREVAIL OVER THE CENTRAL CARIBBEAN AND 
WILL CONTINUE THROUGH THU BEFORE THE DEEP LAYER HIGH PRES TO THE 
NORTH BRAKES DOWN...DECREASING THE PRES GRADIENT BETWEEN IT AND 
CLIMATOLOGICAL LOW PRES OVER NORTHERN COLOMBIA. 1019 MB HIGH 
PRES CURRENTLY RESIDES NEAR 25N68W WITH A RIDGE EXTENDING SE OF 
THE HIGH INTO THE LESSER ANTILLES. A FRONTAL BOUNDARY LIES OVER 
THE WESTERN N ATLC INTO SOUTH FLORIDA AND TO LOW PRES IN THE 
GULF OF MEXICO. THE COLD FRONTAL PORTION OF THIS BOUNDARY WILL 
ADVANCE INTO THE CENTRAL ATLC WHILE THE REMAINDER STAYS 
RELATIVELY STATIONARY OVER FL AND THE GULF ON THU. THE HIGH PRES 
RIDGE WILL WEAKEN AND SHIFT SLIGHTLY SOUTHWARD AS A RESULT OF 
THE ADVANCING PORTION OF THE FRONT. CONDITIONS WILL CHANGE 
RAPIDLY ON FRI AS THE AFOREMENTIONED SURFACE LOW IN THE GULF 
INTENSIFIES AND MOVES EASTWARD...SHIFTING THE SURFACE RIDGE WELL 
E OF THE AREA. THE COLD FRONT ASSOCIATED WITH THIS GULF LOW WILL 
MOVE INTO THE YUCATAN CHANNEL FRI NIGHT. SHOWERS AND 
THUNDERSTORMS WILL BUILD OVER THE NW GULF FRI IN ADVANCE OF THE 
FRONT. WINDS WILL DIMINISH TO 20 KT IN THE CENTRAL CARIBBEAN AS 
A RESULT OF THE DECREASED PRES GRADIENT. 

ATLANTIC OCEAN...
A STRONG SURFACE LOW NORTH OF THE FORECAST AREA NEAR 41N33W IS 
GENERATING NW SWELL IN THE 8 TO 16 FOOT RANGE OVER MUCH OF THE 
ATLC FORECAST WATERS E OF 55W. THIS SURFACE LOW IS ASSOCIATED 
WITH A DEEP LAYER GYRE THAT ALSO ENCOMPASSES A SECOND SURFACE 
LOW...1004 MB...OVER FORECAST WATERS NEAR 27N35W. THIS LOW IS 
CURRENTLY PRODUCING 20 TO 25 KT WINDS AND IS EXPECTED TO 
INTENSIFY AS IT LIFTS NORTHEASTWARD...EVENTUALLY OVERTAKING ITS 
COUSIN TO THE NORTH. AS THE SYSTEM REORGANIZES FURTHER 
NORTH...SEAS WILL SUBSIDE TO THE 7 TO 10 FOOT RANGE OVER THE 
NEXT TWO DAYS. FARTHER W...THE COLD FRONT OVER THE WESTERN ATLC 
WILL SLOWLY ADVANCE EASTWARD INTO THE CENTRAL ATLC OVER THE NEXT 
48 HOURS. SEAS BEHIND THE FRONT WILL BUILD TO 8 TO 20 FT BY FRI. 
MEANWHILE...THE SYSTEM IN THE GULF OF MEXICO THAT IS EXPECTED TO 
INTENSIFY AND LIFT NORTHEASTWARD INTO NORTH FLORIDA/SOUTH 
GEORGIA FRI AFTERNOON WILL BE THE FOCUS OF SHOWERS AND 
THUNDERSTORMS BUILDING IN THE WESTERN ATLC FRI.

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

$$
SCHAUER