000 AXNT20 KNHC 131736 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 105 PM EST SAT DEC 13 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...THE ITCZ... THE ITCZ IS CENTERED ALONG 8N11W 4N23W 4N34W 4N42W 2N51W. SCATTERED MODERATE CONVECTION IS S OF 4N BETWEEN 7W-12W. SCATTERED MODERATE CONVECTION IS ALSO WITHIN 60 NM EITHER SIDE OF THE ITCZ AXIS BETWEEN 19W-25W. SIMILAR CONVECTION IS FROM 2N-7N BETWEEN 26W-38W. ...DISCUSSION... GULF OF MEXICO... RELATIVELY COOL AND DRY CONDITIONS ARE PRESENT ACROSS THE GULF REGION IN THE WAKE OF TWO SURFACE COLD FRONTS THAT EXTEND FROM THE W ATLC INTO THE W CARIBBEAN. LOW LEVEL INSTABILITY RESULTING FROM THE PRESENCE OF THIS RELATIVELY COOLER AIR OVER THE WARMER GULF WATERS IS SUPPORTING A LAYER OF SCATTERED TO OVERCAST STRATOCUMULUS CLOUDS ACROSS THE GULF NW OF A LINE FROM 29N84W TO 22N88W...WITH CLEARING SKIES TO THE SE OF THIS LINE. VISIBLE SATELLITE IMAGERY INDICATES THAT THIS CLEARING LINE IS RETREATING NORTHWESTWARD...AS SOUTHERLY TO SOUTHEASTERLY RETURN FLOW CONTINUES ACROSS THE W GULF AROUND A 1030 MB SURFACE HIGH OVER NE ALABAMA 34N86W...WITH AN ASSOCIATED SURFACE RIDGE EXTENDING ACROSS THE GULF. DEEP LAYER SUBSIDENCE IN STRONG WESTERLY AND NORTHWESTERLY FLOW ALOFT IS PRESENT ACROSS THE GULF REGION...WHICH IS BEING ENHANCED IN THE VICINITY OF THE SURFACE RIDGE. THIS DEEP LAYER SUBSIDENCE IS INHIBITING DEEP CONVECTION ACROSS THE GULF REGION. ALSO...UPPER LEVEL MOISTURE IS STREAMING ACROSS THE NW GULF FROM THE E PACIFIC REGION. ADDITIONALLY... STRONG N TO NE SURFACE WINDS ARE BLOWING THROUGH THE ISTHMUS OF TEHUANTEPEC RESULTING IN GALE FORCE WINDS IN THE E PACIFIC REGION. THESE WINDS WINDS ARE FORECAST TO DECREASE BELOW GALE FORCE AT 13/0000 UTC. CARIBBEAN SEA... TWO SURFACE FRONTS EXTEND INTO THE W CARIBBEAN FROM THE W ATLC. ONE OF THESE FRONTS IS STATIONARY AND EXTENDS FROM E CUBA NEAR 21N77W TO 17N82W TO E OF NICARAGUA NEAR 12N83W...WITH A WEAKENING COLD FRONT EXTENDING FROM W CUBA NEAR 23N81W TO 22N83W. LOW LEVEL CONVERGENCE AND INCREASED DEEP MOISTURE OVER THE SW CARIBBEAN IS SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WITHIN 120 NM EITHER SIDE OF THE STATIONARY FRONT S OF 15N. THIS ACTIVITY IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE ASSOCIATED WITH AN UPPER RIDGE WITH AN AXIS THAT EXTENDS FROM N COLOMBIA NEAR 11N74W TO 15N77W TO 16N79W. THIS ACTIVITY IS ALSO BEING ENHANCED BY LOW LEVEL CONVERGENCE IN THE VICINITY OF A 1010 MB SURFACE LOW IN N COLOMBIA NEAR 9N74W. FARTHER TO THE N AND E...DEEP CONVECTION IS BEING INHIBITED IN THE VICINITY OF THE STATIONARY FRONT ALONG AND N OF 15N...AS WELL AS IN THE VICINITY OF THE WEAKENING COLD FRONT...AND ACROSS MUCH OF THE N AND E CARIBBEAN...WHERE DEEP LAYER DRY AIR IS PRESENT. ALSO...TO THE W OF THESE FRONTS...A RELATIVELY COOLER AND DRIER AIRMASS IS IN PLACE. ACROSS MUCH OF THE CENTRAL AND E CARIBBEAN REGION...MODERATE TO FRESH TRADE WINDS ARE OCCURRING. ATLANTIC OCEAN... MOIST SOUTHWESTERLY FLOW ALOFT IS PRESENT OVER PORTIONS OF THE W ATLC...AS A DEEP TROUGH OVER THE E CONUS AND W ATLC CONTINUES PROGRESSING EASTWARD. AT THE SAME TIME...AN ASSOCIATED SURFACE STATIONARY FRONT...WHICH ALSO ENTERS THE W CARIBBEAN FROM THE W ATLC...EXTENDS FROM E CUBA NEAR 21N77W TO 21N76W...WITH A SURFACE COLD FRONT EXTENDING FROM 21N76W TO 26N71W TO 32N67W TO N OF THE DISCUSSION AREA. INSTABILITY TO THE E OF THE COLD FRONT...AND LOW LEVEL CONVERGENCE IN THE VICINITY OF THE COLD FRONT...ARE SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ALONG AND WITHIN 90 NM E OF THE COLD FRONT N OF 25N...WITH DEEP LAYER DRY AIR INHIBITING DEEP CONVECTION FARTHER TO THE SOUTH. THIS SHOWER AND THUNDERSTORM ACTIVITY IS BEING ENHANCED BY LOW LEVEL CONVERGENCE ASSOCIATED WITH A SURFACE TROUGH...LOCATED TO THE E OF THE COLD FRONT...THAT EXTENDS FROM 24N69W TO 28N68W TO 30N67W. TO THE W OF THIS SURFACE COLD FRONT...A WEAKENING SURFACE COLD FRONT...WHICH ALSO EXTENDS INTO THE W CARIBBEAN FROM THE W ATLC...EXTENDS FROM W CUBA NEAR 23N81W TO 26N76W TO 30N72W. DEEP LAYER DRY AIR IS INHIBITING DEEP CONVECTION NEAR THIS WEAKENING COLD FRONT. RELATIVELY COOLER AND DRIER CONDITIONS ARE PRESENT TO THE W OF THESE COLD FRONTS. TO THE E...A SHARP UPPER TROUGH IS PRESENT WITH AN AXIS THAT EXTENDS FROM 19N45W TO 27N53W TO 32N53W TO N OF THE DISCUSSION AREA...WITH AN ASSOCIATED SURFACE TROUGH EXTENDING FROM 20N50W TO 24N52W TO 27N54W. LOW LEVEL CONVERGENCE ASSOCIATED WITH THE SURFACE TROUGH IS SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS FROM 18N-28N BETWEEN 39W-51W...WHICH ARE BEING ENHANCED BY ATMOSPHERIC INSTABILITY ASSOCIATED WITH THE UPPER TROUGH. COMPUTER MODEL GUIDANCE INDICATES THAT DEEP ATMOSPHERIC LIFT ASSOCIATED WITH THE AFOREMENTIONED DEEP TROUGH OVER THE E CONUS AND W ATLC IS FORECAST TO INTERACT WITH THIS SURFACE TROUGH...RESULTING IN SURFACE PRESSURE FALLS AND THE DEVELOPMENT OF A SURFACE LOW OVER THE CENTRAL ATLC EARLY NEXT WEEK. FARTHER TO THE E...SUBSIDENCE AROUND A 1040 MB SURFACE HIGH W OF THE AZORES NEAR 37N37W IS SUPPORTING FAIR WEATHER CONDITIONS ACROSS MUCH OF THE E ATLC. HOWEVER...UPPER LEVEL DIVERGENCE ASSOCIATED WITH AN UPPER LEVEL JET MAXIMUM OVER THE E ATLC IS SUPPORTING SCATTERED SHOWERS FROM 13N-18N BETWEEN 30W-41W. FARTHER TO THE S...A SURFACE TROUGH EXTENDS FROM 14N55W TO 11N57W TO 8N58W...WHERE VISIBLE SATELLITE IMAGERY INDICATES CYCLONIC MOTION OF LOW LEVEL CLOUD ELEMENTS. HOWEVER...DEEP LAYER DRY AIR IS INHIBITING DEEP CONVECTION NEAR THIS SURFACE TROUGH. ACROSS THE TROPICAL ATLC...WESTERLY FLOW ALOFT IS PRESENT...WITH UPPER LEVEL DIFFLUENCE ENHANCING THE CONVECTION IN THE VICINITY OF THE ITCZ. $$ COHEN