000
AXNT20 KNHC 211743
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST WED JAN 21 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 1715 UTC.

...THE ITCZ...
FROM 5N9W IN LIBERIA TO THE EQUATOR AT 22W INTO NORTHEASTERN 
BRAZIL NEAR 4S38W. ISOLATED MODERATE TO STRONG CONVECTION IS 
OBSERVED WITHIN 60 NM OF THE ITCZ AXIS FROM 13W TO 27W.  
ISOLATED MODERATE TO STRONG CONVECTION IS OBSERVED WITHIN 240 
NM N AND 120 NM S OF THE AXIS WEST OF 27W.
 
...DISCUSSION...

THE GULF OF MEXICO AND THE ATLANTIC OCEAN WEST OF 68W...
A STRONG COLD AIR OUTBREAK IS CURRENTLY OCCURRING ACROSS THE 
GULF AND THE WESTERN ATLANTIC BEHIND A COLD FRONT THAT EXTENDS 
FROM 31N68W DOWN TO THE SOUTHEASTERN BAHAMAS.  SURFACE WINDS ARE 
GENERALLY NORTHERLY AT 20 KT IN THE GULF AND NORTHWESTERLY 20 TO 
30 KT IN THE WESTERN ATLANTIC BEHIND THE FRONT.  WINDS SHOULD 
RELAX BY TOMORROW AS SURFACE RIDGING SETTLES IN OVER FLORIDA AND 
THE NORTHERN GULF.  DESPITE THE COLD AIR ADVECTION DIMINISHING 
...EXPECT ANOMALOUSLY COLD TEMPERATURES TONIGHT BY RADIATIVE 
COOLING...ESPECIALLY OVER LAND.  NO DEEP CONVECTION IS OBSERVED 
IN THE REGION BECAUSE OF THE STABLE AND DRY AIR MASS THAT IS  
PREVAILING.  IN THE UPPER LEVELS...A SHARP SHORT-WAVE TROUGH IS 
OBSERVED OVER THE SOUTHEASTERN US...WHICH IS SUPPORTING THE COLD 
FRONT AND COLD AIR ADVECTION.

THE CARIBBEAN SEA...
THE AFOREMENTIONED COLD FRONT EXTENDS FROM EASTERNMOST CUBA 
SOUTH-SOUTHWESTWARD TO JAMAICA AND TO THE COAST OF NICARAGUA.  
NORTHERLY SURFACE WINDS OF UP TO 25 KT ARE OCCURRING WEST OF THE 
FRONTAL BOUNDARY WITH SIGNIFICANT COOL AND DRY AIR ADVECTION.  A 
PRE-FRONTAL TROUGH...THE REMNANTS OF AN EARLIER COLD FRONTAL 
BOUNDARY...EXTENDS FROM JUST NORTH OF THE TURKS AND CAICOS 
ACROSS WESTERN HAITI SOUTHWESTWARD DOWN TO 15N77W.  NEITHER 
FEATURE IS CURRENTLY PRODUCING ANY SIGNIFICANT DEEP CONVECTION 
...THOUGH BOTH ARE ASSOCIATED WITH ISOLATED SHOWERS.  DURING THE 
NEXT DAY...WHILE THE FRONT SHOULD BECOME STATIONARY SOON...THE 
NORTHERLY WINDS WILL ONLY GRADUALLY WEAKEN.  EAST OF THE 
FRONT...SURFACE WINDS ARE GENERALLY EASTERLY 15 KT OR LESS AND 
ARE EXPECTED TO REMAIN THIS WAY THROUGH THURSDAY.  IN THE UPPER 
LEVELS...A WEAK HIGH IS AT 14N65W.  THE REST OF THE UPPER LEVELS 
IS DOMINATED BY SOUTHWESTERLIES OF UP TO 80 KT ON THE SOUTHEAST 
SIDE OF THE VIGOROUS SHORT-WAVE TROUGH MENTIONED ABOVE.

THE REST OF THE ATLANTIC OCEAN EAST OF 68W...
A LARGE SURFACE 1033 MB HIGH NEAR 31N30W DOMINATES THE NORTH 
ATLANTIC WITH EAST TO NORTHEAST SURFACE WINDS UP TO 25 KT SOUTH 
OF THE HIGH.  A SURFACE TROUGH IS LOCATED ALONG 31N61W TO 
28N64W.  ISOLATED MODERATE CONVECTION IS OBSERVED WITHIN 60 NM 
OF THE TROUGH AXIS.  ELSEWHERE...NO DEEP CONVECTION IS EVIDENT 
THROUGHOUT THE REGION AWAY FROM THE ITCZ.  ALOFT...UPPER LEVEL 
RIDGING PREVAILS ALONG 30N WITH GENERAL SUBSIDENCE ALONG AND 
SOUTH OF THE RIDGE.  AN UPPER LOW IS LOCATED NEAR 15N50W WHICH 
IS DRAWING SOME MID TO UPPER LEVEL CLOUDINESS NORTHWESTWARD ON 
ITS NORTHEASTERN SEMICIRCLE.  NUMEROUS CIRRUS CLOUDS ARE ALSO 
OBSERVED EQUATORWARD OF 15N BEING ADVECTED FROM THE ITCZ 
CONVECTION.

$$
CWL