[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 180834
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
105 AM EST THU DEC 18 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0515 UTC.

...THE ITCZ...
ITCZ IS CENTERED ALONG 10N14W 5N21W 5N37W 5N53W. SCATTERED
MODERATE CONVECTION IS WITHIN 180 NM EITHER SIDE OF THE AXIS
BETWEEN 16W-30W. SCATTERED MODERATE IS WITHIN 120 NM N AND 240
NM S OF THE AXIS BETWEEN 40W-47W.

...DISCUSSION...

GULF OF MEXICO...
A LARGE AND FAIRLY AMPLIFIED MID TO UPPER HIGH IS CENTERED OVER
THE BAY OF CAMPECHE PROVIDING MAINLY LIGHT FLOW AND STABLE AIR
ALOFT....EXCEPT FOR OVER FLORIDA WHERE HIGH CLOUDINESS IS BEING
DRIVEN S ON THE E PERIPHERY OF THE RIDGE. IN THE LOWER
LEVELS...A DISSIPATING FRONT IS STILL STALLED ALONG THE TEXAS
AND MEXICO COASTS. SLIGHT LOW-LEVEL CONVERGENCE ALONG THE FRONT
IS PRODUCING LOW-LEVEL CLOUDS AND LIGHT SHOWERS. OTHERWISE...
MAINLY FAIR CONDITIONS EXIST ELSEWHERE WITH ONLY PATCHY
LOW-LEVEL CLOUDS DRIVEN BY LIGHT TO MODERATE E FLOW ON THE S/SW
SIDE OF A 1026 MB HIGH OVER THE SUBTROPICAL W ATLC. LITTLE
SIGNIFICANT CHANGE IS EXPECTED OVER THE NEXT COUPLE OF DAYS
UNTIL THE NEXT COLD FRONT APPROACHES THE NW GULF THIS WEEKEND.

CARIBBEAN SEA...
CONFLUENCE NEAR THE BASE OF AN UPPER TROUGH OVER THE CENTRAL
ATLC IS ENHANCING SUBSIDENCE ACROSS THE ENTIRE AREA...LIMITING
THE DEVELOPMENT OF ANY DEEP CONVECTION. HOWEVER...SCATTERED
SHOWERS AND LOW TOPPED TSTMS ARE AFFECTING MUCH OF THE
AREA...BENEATH THE MID-LEVEL CAP...GENERATED BY AN ELONGATED SFC
TROUGH OVER THE CENTRAL ATLC AND DRIVEN SOUTH BY STIFF N/NE
WINDS ON THE W SIDE OF THE CIRCULATION. N TO NE WINDS IN THE
CARIBBEAN ARE MAINLY IN THE 20-25 KT RANGE W OF 67W. SIMILAR
WINDS/SHOWERS ARE EXPECTED OVER THE NEXT COUPLE OF DAYS BEFORE
HIGH PRES SHIFTS S OVER THE W ATLC ALLOWING THE FLOW TO WEAKEN
AND VEER E.

ATLANTIC OCEAN...
DEEP LAYER LOW PRESSURE OVER THE CENTRAL ATLC IS CAUSING SOME
ACTIVE WEATHER TONIGHT...BUT MUCH LESS SO THAN A DAY OR TWO AGO.
THE SFC CENTER IS ANALYZED 1010 MB NEAR 26N58W WITH ITS
ASSOCIATED TROUGH EXTENDING BOTH N TO 30N56W AND S TO 21N62W.
SCATTEROMETER AND TO SOME DEGREE SFC OBS SHOW A FAIRLY WELL
DEFINED SFC CIRCULATION WITHIN AN INCREASINGLY ELONGATED TROUGH.
LOW-LEVEL CONVERGENCE AND INSTABILITY NEAR THE LOW IS PRODUCING
SCATTERED SHOWERS AND TSTMS WITHIN 240 NM OF THE CENTER. A
LARGER AREA OF SHOWERS AND TSTMS EXIST FARTHER E FROM 12N-29N
BETWEEN 46W-51W IN AN UPPER DIFFLUENT ZONE. THIS LOW IS EXPECTED
BECOME GREATLY SHEARED AND SPLIT APART BY A SHORTWAVE TROUGH
LATER THIS WEEK AND WEEKEND. THE W ATLC IS RELATIVELY TRANQUIL
BENEATH ABUNDANT DRY AIR ALOFT ON THE W SIDE OF THE UPPER LOW.
HOWEVER...AS MENTIONED ABOVE... STRONG N/NE LOW-LEVEL WINDS AND
INSTABILITY ARE STIRRING UP SHOWERS AND LOW-TOPPED TSTMS MAINLY
E OF 75W. OVER THE TROPICAL E ATLC...STRONG WLY FLOW ALOFT IS
TRANSPORTING WIDESPREAD MID-HIGH LEVEL CLOUDINESS AND ENHANCING
ITCZ CONVECTION.

$$
CANGIALOSI





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