[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 142357
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 PM 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...THE ITCZ...
ITCZ IS CENTERED ALONG 7N11W 4N20W 4N35W 4N53W. SCATTERED
MODERATE TO STRONG CONVECTION IS WITHIN 60-80 NM S OF THE AXIS
BETWEEN 22W-33W...AND WITHIN 45 NM N OF THE AXIS BETWEEN
33W-37W. SCATTERED MODERATE CONVECTION IS ALSO NOTED FROM 5N-11N
BETWEEN 38W-52W LIKELY ASSOCIATED WITH A SFC TROUGH EMBEDDED
WITHIN THE ITCZ.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER-LEVEL RIDGE CENTERED ON A HIGH OVER THE NW CARIBBEAN
DOMINATES THE ENTIRE GULF. STRONG W TO NW MID-UPPER FLOW...ON
THE N PERIPHERY OF THIS RIDGE...IS SPREADING CONSIDERABLE
PACIFIC MOISTURE ACROSS NORTHERN MEXICO AND THE GULF REGION N OF
25N. CONVECTIVE CLOUDS STREETS ARE FORMING PARALLEL TO THE SLY
RETURN FLOW PARTICULARLY OVER THE WESTERN HALF OF THE GULF.
DRIER AIR IS PRESENT S OF 25N CLOSER TO THE UPPER RIDGE AXIS. AT
THE SURFACE...STRONG HIGH PRES OVER THE W ATLC IS MAINTAINING
STRONG E TO SE WINDS OVER THE E GULF AND SE TO S WINDS OVER THE
REMAINDER OF THE AREA. AN EARLIER ASCAT PASS SHOWED SLY WINDS OF
25 KT WEST OF 95W. THESE WINDS WILL BECOME MORE UNIFORM S TO SE
TONIGHT AND MON AS THE NEXT COLD FRONT APPROACHES THE TEXAS
COAST MON AFTERNOON...INCREASING THE CHANCE OF SHOWERS OVER THE
NW PORTION OF THE GULF. THE FRONT IS FORECAST TO MOVE OFF THE
TEXAS COAST MON NIGHT AND STALL IN THE COASTAL WATERS EARLY TUE
BEFORE GRADUALLY MOVING BACK INLAND AROUND MID WEEK.

CARIBBEAN SEA...
AN UPPER-LEVEL HIGH CENTERED OVER THE GULF OF HONDURAS IS
PRODUCING N TO NW FLOW OVER THE CENTRAL AND EASTERN CARIBBEAN
AND ABUNDANT DRY SINKING AIR OVER MUCH OF THE AREA. A FEW
PATCHES OF LOW LEVEL MOISTURE ARE SEEN ACROSS THE REGION MORE
CONCENTRATED NEAR THE ABC ISLANDS WHERE A WEAK SFC TROUGH IS
ANALYZED. THE TROUGH LIES ALONG 66W/67W SOUTH OF 15N. SCATTERED
SHOWERS ARE NEAR THE COAST OF COSTA RICA AND NICARAGUA LIKELY
PRODUCED BY LOW-LEVEL WIND SPEED CONVERGENCE AND A DIFFLUENT
PATTERN ALOFT NEAR THE AFOREMENTIONED UPPER-LEVEL HIGH.
FRAGMENTS OF MOISTURE ARE ALSO MOVING FROM THE ATLC ACROSS E AND
CENTRAL CUBA UNDER AN E-NE WIND FLOW AROUND THE PERIPHERY OF THE
STRONG HIGH PRES SITUATED OVER THE W ATLC NEAR 39N67W. PRES
GRADIENT BETWEEN THIS HIGH AND RELATIVE LOW PRES OVER THE
CARIBBEAN IS RESULTING IN FRESH TRADE WINDS ACROSS THE BASIN.

ATLANTIC OCEAN...
AN UPPER-LEVEL TROUGH OVER THE CENTRAL ATLC MAINLY N OF 30N
SUPPORTS A COLD FRONT THAT ENTERS THE FORECAST AREA NEAR 31N53W
THEN CONTINUES SW TO NEAR 24N68W. AT THIS POINT...IT BECOMES
STATIONARY EXTENDING OVER THE SE BAHAMAS AND THE WINDWARD
PASSAGE. A 1038 MB SFC HIGH LOCATED NEAR 39N67W FOLLOWS THE
FRONT. THIS HIGH ENVELOPS THE EASTERN SEABOARD...CUBA AND THE
BAHAMAS. THE TIGHT PRES GRADIENT BETWEEN THIS SFC HIGH AND THE
FRONT IS PRODUCING A LARGE AREA OF 20-30 KT NE WINDS W OF THE
FRONT.

AS WAS ADVERTISED BY MUCH OF THE COMPUTER MODELS...A SFC LOW IS
BEGINNING TO FORM OVER THE CENTRAL ATLC NEAR 28N54W. THE CLOUD
PATTERN IS EXHIBITING SOME CYCLONIC CIRCULATION WITH SCATTERED
SHOWERS AROUND THE LOW CENTER. THIS SYSTEM WILL DRIFT SW DURING
THE NEXT 24 HOURS AND THEN W TO WSW FOR SEVERAL DAYS. THE PRES
GRADIENT IS EXPECTED TO INCREASE BETWEEN THIS DEVELOPING LOW AND
THE SFC HIGH CURRENTLY OVER THE W ATLC WITH WINDS REACHING GALE
FORCE ON THE WESTERN SIDE OF THE SFC LOW. AN UPPER-LEVEL TROUGH
RUNNING FROM 29N56W TO 19N44W IS GENERATING A LARGE AREA OF
SCATTERED SHOWERS AND ISOLATED TSTMS N OF 20N BETWEEN 40W-50W.
THE SFC PRES PATTERN IS ALSO VERY TIGHT BETWEEN THE DEVELOPING
CYCLONE OVER THE CENTRAL ATLC AND A 1035 MB HIGH JUST W OF THE
AZORES. AS A RESULT...SCATTEROMETER DATA INDICATE A SWATH OF
20-30 KT E TO SE WINDS ACROSS THE E ATLC PARTICULARLY FROM
15N-24N AND EST OF 40W. MAINLY WESTERLY ZONAL FLOW ALOFT
DOMINATES THE DEEP TROPICS...WITH UPPER LEVEL DIFFLUENCE
ENHANCING CONVECTION WITHIN THE ITCZ.

$$
GR








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