AXNT20 KNHC 121739
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 
205 PM EDT SAT 12 APR 2003

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL 
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...AND ATLANTIC OCEAN
TO THE AFRICAN COAST FROM THE EQUATOR TO 32N INCLUDING NORTHERN 
SECTIONS OF SOUTH AMERICA. THE FOLLOWING INFORMATION IS BASED
ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND 
METEOROLOGICAL ANALYSIS.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1715 UTC.

SPECIAL FEATURES...
NONE.

TROPICAL WAVES/ITCZ...
AXIS OF ITCZ-RELATED CLOUDS/CONVECTION IS CENTERED ALONG 1N0 1N20W 
4N41W 2N57W. ISOLATED MODERATE CONVECTION WITHIN 30NM OF THE AXIS 
BETWEEN 27W-38W. SCATTERED MODERATE FROM THE EQUATOR TO THE AXIS 
BETWEEN 46W-54W ALONG THE COAST OF BRAZIL. SEE SIGNIFICANT 
CLOUDS/CONVECTION FOR LARGE CONVECTIVE COMPLEX IN ERN ATLC.

MIDDLE/UPPER LEVEL SYNOPTIC FEATURES...

GULF OF MEXICO AND WRN ATLC...THE LARGE MID/UPPER LEVEL TROUGH WHICH 
HAS PLAGUED THE EAST COAST OF THE U.S. OVER THE PAST SEVERAL DAYS 
CONTINUES TO LIFT NE TOWARDS THE CANADIAN MARITIMES BUT THE FAR SRN 
REACHES OF THE CYCLONIC CIRCULATION CONTINUE TO LIE ACROSS THE 
GLFMEX..FLORIDA...AND THE SW ATLC. THE JET STREAK AT THE BASE OF THE 
TROUGH REMAINS QUITE VIGOROUS...WITH THE 1200 UTC RAOB AT MIAMI 
INDICATING 105 KT AT 250 MB. THE TROUGH ITSELF IS COMPOSED OF TWO 
SEPARATE SHORTWAVES...ONE OF WHICH IS LOCATED OVER THE WRN ATLC AND 
IS ASSOCIATED WITH THE MAIN SURFACE COLD FRONT NEAR BERMUDA. A 
SECOND SHORTWAVE IS DROPPING S FROM THE SRN PLAINS OF THE U.S. INTO 
THE NW GLFMEX BUT IS ONLY PRODUCING A NEGLIGIBLE INCREASE IN CLOUDS 
OVER THE CNTRL GULF. IN FACT...UPPER LEVEL MOISTURE IS HARD TO COME 
BY ACROSS THE REGION WITH A STRONG CAPPING INVERSION LOCATED NEAR 
700 MB AND EXTREMELY DRY AIR ABOVE THAT. THERE IS SOME MOIST AIR 
LOCATED IN THE LOW-LEVELS BELOW 700 MB BUT SURFACE HIGH PRESSURE AND 
NWLY WINDS OVER THE ERN GLFMEX IS PREVENTING THE JUICIEST AIR FROM 
MAKING ITS WAY BACK TO THE N FROM THE CARIBBEAN. ALL IN 
ALL...DEFINITELY A PLEASANT DAY WHICH SHOULD ONLY IMPROVE OVER THE 
NEXT COUPLE OF DAYS AS AN UPPER LEVEL RIDGE ORIENTS ITSELF FROM 
MEXICO TO THE OHIO VALLEY BY MONDAY. AS FOR THE WRN ATLC...THE 
STRONG WLY/NWLY FLOW IS CLEARING OUT THE INCLEMENT WEATHER. BERMUDA 
REPORTED OVER 3 INCHES OF RAIN YESTERDAY DUE TO THE PASSING COLD 
FRONT...BUT THINGS ARE DEFINITELY LOOKING UP AS THE CONTINENTAL AIR 
MASS CONTINUES TO MOVE E.

CARIBBEAN...VERY FEW OF THE CARIBBEAN ISLANDS HAVE THE LUXURY OF THE 
DRIER AIR NOW COVERING THE GLFMEX. WITH NO PROMINENT UPPER LEVEL 
DYNAMICS LOCATED OVER THE CARIBBEAN...THE STATIONARY FRONT WHICH HAS 
BEEN DRAPED OVER THE CNTRL/WRN CARIBBEAN HAS STAYED PUT. AREAS FROM 
WRN CUBA...THE CAYMAN ISLANDS...AND THE YUCATAN PENINSULA ARE 
PROBABLY ENJOYING THE MOST COMFORTABLE WEATHER IN THE REGION WITH 
LOWER DEWPOINTS N OF THE FRONT. AS FOR UPPER/MID LEVELS...A TRPCL 
RIDGE AXIS LIES ALONG THE NRN SECTIONS OF S AMERICA FROM FRENCH 
GUIANA TO JUST S OF PANAMA AND THIS IS PRODUCING WLY FLOW ACROSS THE 
ENTIRE BASIN. HOWEVER...AS THE FLOW TURNS ANTICYCLONICALLY AROUND 
THE RIDGE AXIS MODERATE CONVERGENCE IS TAKING PLACE OVER THE 
CARIBBEAN AND SO MODERATE SUBSIDENCE IS LOCATED BETWEEN THE S 
AMERICAN COAST AND THE GREATER ANTILLES E OF NICARAGUA/HONDURAS. NO 
IMMEDIATE CHANGES IN THE WEATHER ARE ANTICIPATED EXCEPT FOR A 
GRADUAL INCREASE IN LOW-LEVEL MOISTURE AS THE STATIONARY FRONT 
BEGINS TO MOVE BACK TO THE N ACROSS THE NW CARIBBEAN. THE 12Z GFS 
RUN INDICATES A BLOW-UP OF CONVECTION MOVING NE FROM THE TURKS AND 
CAICOS ISLANDS BY LATE SUNDAY BUT IS THE ONLY MAJOR WEATHER-PRODUCER 
FORESEEN IN THE NEAR FUTURE.

CNTRL ATLC...THERE IS A LOT OF ACTIVITY GOING ON IN THE MID/UPPER 
LEVELS BUT IT IS PRODUCING NO SIGNIFICANT WEATHER AT THE SURFACE. A 
MID LEVEL ANTICYCLONE IS CENTERED ABOUT 750NM NE OF ANTIGUA WITH A 
RIDGE AXIS EXTENDING SW TO THE WINDWARD ISLANDS...AND A SECOND RIDGE 
EXTENDING N BEYOND 32N50W. ON THE FLIP SIDE...A MID/UPPER LEVEL 
TROUGH EXTENDS FROM NEAR THE VENEZUELA/GUYANA BORDER TO A MID-LEVEL 
LOW NEAR 18N47W CONTINUING NE TO A LARGE POLAR LOW NEAR THE AZORES. 
THE ONLY INFLUENCE THESE TWO SYSTEMS ARE REALLY PRODUCING IS AN AREA 
OF CONVERGENCE AND STRONG SUBSIDENCE FROM 16N-22N BETWEEN 47W-56W 
AND MODERATE SUBSIDENCE IN A MUCH LARGER REGION FROM 7N-30N E OF THE 
LESSER ANTILLES. THIS HAS MADE THE SKY CIRRUS-FREE OVER THE 
AREA...BUT IT HAS NOT STOPPED SCATTERED STRATOCUMULUS IN THE 
LOW-LEVELS FROM FORMING. THE RIDGE AND TROUGH WILL REMAIN STATIONARY 
THROUGH LATE MONDAY COUPLED IN A WEAK UPPER LEVEL FLOW SINCE THEY 
ARE EMBEDDED IN A MUCH LARGE RIDGE WHICH EXTENDS FAR INTO THE N 
ATLC. THE LOW/MID LEVEL HIGH HOWEVER WILL ALSO REMAIN IN PLACE AND 
WILL PREVENT MUCH CONVECTION ASSOCIATED WITH THE WRN ATLC COLD FRONT 
FROM MAKING ITS WAY INTO THE CNTRL ATLC.

ERN ATLC...TROUGHING IN THE CNTRL ATLC GIVES WAY TO RIDGING IN THE 
ERN ATLC WITH THE EVER-PRESENT TRPCL JET STREAMING JUST N OF THE 
CAPE VERDE ISLANDS. THE TRPCL RIDGE THAT IS LOCATED OVER S AMERICA 
CONTINUES EWD ACROSS THE ATLC ALONG 5N TO A CLOSED ANTICYCLONE NEAR 
8N20W AND THEN EWD INTO SUB-SAHARAN AFRICA. AS IS USUALLY THE 
CASE...THE POSITION OF THE RIDGE AND THE TROUGH NEAR THE AZORES HAS 
PRODUCED A 70-90 KT JET FROM 12N40W TO THE COAST OF MAURITANIA... 
WITH SOME CIRRUS OUTFLOW FROM THE ITCZ BEING ENTRAINED INTO THE 
ENTRANCE OF THE JET. IMMEDIATELY TO THE N...CONVERGENCE IS PRODUCING 
STRONG SUBSIDENCE FROM 20N-25N E OF 20W INTO SRN MOROCCO/NRN 
MAURITANIA. OVER THE NEXT SEVERAL DAYS THE TRPCL JET WILL BEGIN TO 
MERGE WITH THE MUCH STRONGER JET NEAR THE AZORES AS THE WHOLE SYSTEM 
MOVES ONSHORE INTO WRN AFRICA.

SURFACE SYNOPTIC FEATURES...
LARGE HIGH PRESSURE COMPLEX OVER THE GLFMEX WITH A 1018 MB HIGH 
CENTERED NEAR 26N92W AND OVER THE FLORIDA STRAITS NEAR 24N82W.

COLD FRONT IN THE WRN ATLC STRETCHES FROM 32N62W TO 21N74W OVER ERN 
CUBA...CONTINUING ACROSS THE WRN CARIBBEAN AS A STATIONARY FRONT TO 
18N80W 12N82W. A WEAK POST-FRONTAL TROUGH EXTENDS FROM 32N66W TO 
25N73W PRIMARILY SEPARATING WEAKER WINDS IMMEDIATELY BEHIND THE 
FRONT FROM STRONGER WINDS TO THE NW. SCATTERED MODERATE CONVECTION 
UP TO 180NM AHEAD OF THE FRONT N OF 22N. PATCHY LOW CLOUDS WITH 
ISOLATED SHOWERS BETWEEN JAMAICA AND HAITI AS WELL AS BETWEEN THE 
STATIONARY FRONT AND THE NICARAGUAN COAST.

1027 MB HIGH IN THE CNTRL ATLC NEAR 27N44W WITH A RIDGE AXIS 
EXTENDING WSW TO HISPANIOLA AND E TO THE MOROCCAN COAST. SHIP 
OBSERVATIONS AND QUIKSCAT IMAGERY INDICATE MODERATE TRADES UP TO 25 
KT FROM 10N-20N BETWEEN 35W AND THE LESSER ANTILLES.

WELL-DEFINED COLD FRONT MOVING S INTO THE SUBTRPCL ERN/CNTRL ATLC 
FROM 32N22W 28N30W 28N40W 31N47W. VISIBLE IMAGERY CLEARLY SHOWS A 
DISTINCT ROPE CLOUD ALONG THE FRONT WITH ISOLATED SHOWERS OR TSTMS 
ALONG THIS LINE N OF 28N.

SIGNIFICANT CLOUDS/CONVECTION...
GULF OF MEXICO...
BROKEN LOW/MID LEVEL CLOUDS IN THE BAY OF CAMPECHE S OF 20N AND 
WITHIN 90NM OF THE E COAST OF MEXICO BETWEEN TUXPAN AND LA CRUZ 
MEXICO. SCATTERED HIGH CLOUDS ALSO OVER THE BAY OF CAMPECHE S OF 
20N. FEW CUMULUS CLOUDS ACROSS THE CNTRL GULF FROM 24N-28N BETWEEN 
86W-91W.

CARIBBEAN SEA...
SEE SURFACE SYNOPTIC FEATURES.
 
TROPICAL ATLANTIC...
SEE ITCZ. ELSEWHERE...A LARGE CONVECTIVE SURGE THAT MOVED OFF THE 
COAST OF IVORY COAST/LIBERIA AROUND 0000 UTC HAS MOVED SW INTO THE 
ITCZ REGION AND HAS BEGUN TO SPLIT. NUMEROUS MODERATE/ISOLATED 
STRONG CONVECTION FROM EQ-3N BETWEEN 10W-15W. NUMEROUS 
MODERATE/ISOLATED STRONG FROM EQ-4N BETWEEN 16W-20W. WIDELY 
SCATTERED MODERATE S OF 1N BETWEEN 20W-27W. A SECOND SURGE OF 
CONVECTION APPEARS TO BE MOVING QUICKLY ACROSS GHANA AND WILL MOST 
LIKELY MAKE ITS WELL INTO THE ERN ATLC LATER TONIGHT.

SUBTROPICAL ATLANTIC...
SEE SURFACE SYNOPTIC FEATURES.

$$
BERG