[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 182341
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST TUE DEC 18 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 07N11W TO
06N14W. THE INTERTROPICAL CONVERGENCE ZONE AXIS EXTENDS FROM
06N14W TO 04N21W TO 05N37W TO 04N43W. WIDELY SCATTERED MODERATE
CONVECTION IS FROM THE EQUATOR TO 07N BETWEEN 10W-40W...AND FROM
THE EQUATOR TO 09N BETWEEN 40W-51W.

...DISCUSSION...

GULF OF MEXICO...
WATER VAPOR IMAGERY INDICATES A VIGOROUS MID-LEVEL SHORTWAVE
TROUGH IS PROGRESSING EASTWARD OFF THE CAROLINA COAST THIS
EVENING IN THE VICINITY OF 33N76W. THIS FEATURE SUPPORTS A COLD
FRONT THAT AS OF 18/2100 UTC IS ANALYZED FROM MELBOURNE TO
SARASOTA FLORIDA AND INTO THE GULF W-SW TO 25N90W. THE FRONT
REMAINS PRECIPITATION-FREE ACROSS THE GULF WATERS THIS
EVENING...HOWEVER THE MAIN IMPACT WITH THE FRONT IS THE
NOTICEABLE DIFFERENCE IN AIRMASS CONTRAST WITH DEWPOINTS NORTH
OF THE FRONT CONSIDERABLY DRIER THAN THOSE ACROSS THE SOUTHERN
FLORIDA PENINSULA AND PORTIONS OF THE SE GULF. MOSTLY DRY
CONDITIONS ARE NOTED ON WATER VAPOR IMAGERY THIS EVENING OVER
THE REMAINDER OF THE BASIN AS WEAK HIGH PRESSURE CONTINUES TO
DOMINATE. A 1017 MB HIGH IS CENTERED NEAR 30N87W AND IS EXPECTED
TO SLOWLY SHIFT EASTWARD AND INTO THE SW NORTH ATLC BY LATE
WEDNESDAY. AS THIS OCCURS...WINDS WILL VEER AND BECOME MORE
SOUTHERLY THROUGH EARLY THURSDAY AS A STRONG LOW PRESSURE AREA
DEVELOPS OVER THE CENTRAL PLAINS AND MID-MISSISSIPPI RIVER
VALLEY. THE NEXT COLD FRONT IS FORECAST TO EMERGE OFF THE TEXAS
AND LOUISIANA COAST THURSDAY MORNING.

CARIBBEAN SEA...
CONDITIONS ACROSS THE CARIBBEAN SEA BASIN REMAIN FAIRLY TRANQUIL
THIS EVENING AS WATER VAPOR IMAGERY INDICATES VERY DRY AIR AND
SUBSIDENCE PREVAILS ALOFT. AN UPPER LEVEL ANTICYCLONIC
CIRCULATION IS CENTERED NEAR 20N66W AND INFLUENCES MUCH OF THE
NE CARIBBEAN WHILE AN UPPER LEVEL TROUGH IS CENTERED OVER THE SW
CARIBBEAN NEAR 13N77W. AT THE SURFACE...A FAIRLY WEAK PRESSURE
GRADIENT IS IN PLACE ACROSS THE CARIBBEAN WITH TRADES REMAINING
IN THE RANGE OF 10 TO 20 KT THROUGH THE OVERNIGHT PERIOD INTO
WEDNESDAY. POSSIBLE ISOLATED LOW-TOPPED SHOWERS ARE OCCURRING
OVER THE NW CARIBBEAN AND PORTIONS OF CENTRAL AMERICA FROM
11N-22N BETWEEN 80W-87W AND OVER THE EASTERN CARIBBEAN E OF 70W.
THE TRADE WINDS ARE FORECAST TO INCREASE GRADUALLY BETWEEN
70W-80W THURSDAY INTO FRIDAY WEAKEN AGAIN THEREAFTER AS A COLD
FRONT WILL MOVE INTO THE NW CARIBBEAN LATE FRIDAY INTO SATURDAY.

ATLANTIC OCEAN...
A MID-LEVEL SHORTWAVE TROUGH IS CENTERED OFFSHORE OF THE
CAROLINAS NEAR 33N76W THAT SUPPORTS A COLD FRONT ANALYZED FROM
32N76W TO MELBOURNE FLORIDA NEAR 28N81W. THE FRONT REMAINS FREE
OF PRECIPITATION THIS EVENING...HOWEVER TO THE EAST OF THE FRONT
IN THE AREA OF MAXIMUM MIDDLE TO UPPER LEVEL DIFFLUENCE...WIDELY
SCATTERED SHOWERS AND ISOLATED TSTMS ARE OCCURRING N OF 30N
BETWEEN 50W AND THE FRONT. THIS AREA CONTINUES TO RESIDE IN THE
WARM SECTOR OF A COMPLEX AREA OF LOW PRESSURE CENTERED OFF THE
NEW ENGLAND COAST IN THE WESTERN NORTH ATLC. OTHERWISE...THE
REMAINDER OF THE SW NORTH ATLC IS UNDER THE INFLUENCE OF A
SURFACE RIDGE ANCHORED BY A 1020 MB HIGH CENTERED IN THE CENTRAL
ATLC NEAR 32N46W. THE RIDGE AXIS EXTENDS FROM THE HIGH SW TO THE
SE BAHAMAS NEAR 22N73W. MOSTLY FAIR CONDITIONS ARE NOTED ON
SATELLITE IMAGERY THIS EVENING WITH ONLY A FEW ISOLATED LOW-
TOPPED SHOWERS OCCURRING FROM 21N-28N BETWEEN 69W-74W.
FINALLY...AN UPPER LEVEL TROUGH IS OVER THE EASTERN ATLC WITH
AXIS EXTENDING FROM 28N37W TO A BASE NEAR 16N50W. THIS TROUGHING
SUPPORTS A COLD FRONT ANALYZED INTO THE DISCUSSION AREA NEAR
32N29W THAT EXTENDS SW TO 24N43W. A WEAK PRE-FRONTAL SURFACE
TROUGH IS FROM 25N40W TO 20N45W. ISOLATED SHOWERS AND TSTMS ARE
OCCURRING WITHIN 75 NM EITHER SIDE OF THE FRONT.

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

$$
HUFFMAN




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