[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 141129
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 AM EST SUN DEC 14 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1115 UTC.

...THE ITCZ...
ITCZ IS CENTERED ALONG 8N14W 4N20W 5N40W 3N51W. SCATTERED
MODERATE TO STRONG CONVECTION IS WITHIN 150 NM S OF THE AXIS
BETWEEN 19W-27W...WITHIN 120 NM N AND 90 NM S OF THE AXIS
BETWEEN 27W-33W...AND FROM 6N-9N BETWEEN 45W-51W. SCATTERED
MODERATE IS WITHIN 150 NM S OF THE AXIS E OF 15W AND FROM 6N-8N
BETWEEN 35W-38W.

...DISCUSSION...

GULF OF MEXICO...
STRONG W TO NW MID-UPPER FLOW...ON THE N PERIPHERY OF A RIDGE
CENTERED OVER THE YUCATAN PENINSULA...IS SPREADING WIDESPREAD
PACIFIC MOISTURE N OF 25N. ONLY ISOLATED SHOWERS ARE LIKELY
EMBEDDED AS MUCH OF THE MOISTURE APPEARS TO BE IN THE FORM OF
MID-HIGH LEVEL CLOUDINESS. DRIER AIR IS PRESENT S OF 25N CLOSER
TO THE UPPER RIDGE AXIS. IN THE LOWER LEVELS...STRONG HIGH PRES
OFF THE MID-ATLC COAST IS MAINTAINING STRONG E TO SE WINDS OVER
THE E GULF AND SE TO S WINDS ELSEWHERE. THESE WINDS WILL BECOME
MORE UNIFORM S TO SE LATER TODAY AND MON AS THE NEXT COLD FRONT
APPROACHES THE TEXAS COAST...INCREASING THE CHANCE OF SHOWERS
OVER THE NW GULF.

CARIBBEAN SEA...
AN UPPER HIGH CENTERED OVER THE YUCATAN PENINSULA HAS HELPED SET
UP ZONAL TO NW FLOW AND ABUNDANT DRY SINKING AIR OVER MUCH OF
THE AREA. ONLY AREA OF SIGNIFICANT MOISTURE IS NEAR THE COAST OF
COSTA RICA AND NICARAGUA...LIKELY PRODUCED BY LOW-LEVEL SPEED
CONVERGENCE (EVIDENT IN QSCAT DATA) AND DIFFLUENCE ALOFT NEAR
THE UPPER HIGH CENTER. HOWEVER...EVEN THIS CONVECTION HAS BEEN
DECREASING IN INTENSITY AND COVERAGE OVER THE PAST FEW HOURS.
OTHERWISE...PATCHES OF LOW-LEVEL MOISTURE WITH EMBEDDED SHOWERS
ARE SCATTERED ACROSS THE REMAINDER OF THE W CARIBBEAN ASSOCIATED
WITH THE REMNANTS OF AN OLD FRONTAL BOUNDARY. LITTLE LARGE SCALE
CHANGES ARE EXPECTED OVER THE NEXT COUPLE OF DAYS.

ATLANTIC OCEAN...
AN UPPER TROUGH ALONG 61W IS FLATTENING BUT STILL PROVIDING SOME
SUPPORT FOR A COLD FRONT EXTENDING FROM 32N58W TO 25N68W THEN
STATIONARY TO THE WINDWARD PASSAGE. THE TIGHT PRES GRADIENT
BETWEEN THE FRONT AND A 1033 MB HIGH OFF THE NEW JERSEY COAST
IS PRODUCING A LARGE AREA OF 20-30 KT NE WINDS W OF THE FRONT.
UPPER DIFFLUENCE E OF THE UPPER TROUGH AXIS IS PRODUCING A SWATH
OF SCATTERED SHOWERS AND TSTMS N OF 28N BETWEEN 57W-60W.

FARTHER E...A WEAKENING UPPER LOW NEAR 27N54W AND A HIGHLY
DIFFLUENT UPPER PATTERN IS PRODUCING A LARGE AREA OF SCATTERED
SHOWERS AND TSTMS N OF 16N BETWEEN 39W-50W. SHORTWAVE IR IMAGES
AND QSCAT DATA REVEALS AN ASSOCIATED SFC TROUGH ALONG 55W N OF
26N...BUT NEARLY ALL OF THE ASSOCIATED WEATHER (OUTLINED ABOVE)
IS LOCATED IN THE DIFFLUENT ZONE TO ITS E. THE SFC PRES PATTERN
IS VERY TIGHT BETWEEN THE TROUGH AND A 1037 MB HIGH JUST W OF
THE AZORES PRODUCING 20-30 KT E WINDS ACROSS THE SUBTROPICAL
ATLC E OF THE TROUGH AXIS. NWP MODELS CONTINUE TO SUGGEST
POSSIBLE LOW PRESSURE DEVELOPMENT DURING THE NEXT FEW DAYS OVER
THE CENTRAL ATLC...ASSOCIATED WITH THE COMBINED EFFECTS OF THE
DEEP LAYER TROUGHING AND THE TAIL END OF THE WEAKENING FRONT
MOVING INTO THE AREA. IN ANTICIPATION OF THE LOW DEVELOPMENT...A
GALE WARNING IS POSTED FOR AN AREA NW OF THE LOW...DUE TO THE
STRONG GRADIENT BETWEEN IT AND HIGH PRES OVER THE N CENTRAL
ATLC. OVER THE FAR TROPICAL E ATLC...AN UPPER JET ALONG 19N/20N
IS ADVECTING ABUNDANT MID-HIGH LEVEL MOISTURE TO ITS S E OF 40W
AND ENHANCING CONVECTION WITHIN THE ITCZ.

$$
CANGIALOSI





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