000 AXNT20 KNHC 132343 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 705 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC. ...THE ITCZ... THE ITCZ IS CENTERED ALONG 9N13W 4N30W 5N45W 4N54W. ISOLATED MODERATE CONVECTION IS WITHIN 120 NM EITHER SIDE OF THE AXIS BETWEEN 18W-40W. SIMILAR CONVECTION IS ALSO NOTED WITHIN 80 NM N OF AXIS BETWEEN 42W-47W...AND NEAR 9N48W. ...DISCUSSION... GULF OF MEXICO... RELATIVELY COOL AND DRY CONDITIONS ARE PRESENT ACROSS THE GULF REGION COURTESY OF A 1029 MB HIGH CENTERED OVER THE SE CONUS. BROKEN COLD AIR STRATOCUMULUS CLOUDS ARE SEEN ON SATELLITE IMAGERY COVERING MUCH OF THE GULF WATERS PARTICULARLY N OF 23N AND WEST OF 85W...WITH CLEARING SKIES JUST WEST OF THE FLORIDA PENINSULA. SURFACE SLY WINDS OF 20 TO 25 KT ARE BLOWING ACROSS THE WESTERN HALF OF THE GULF IN ADVANCE OF A COLD FRONT FORECAST TO APPROACH THE TEXAS COAST MON NIGHT. THIS FRONT WILL MOVE BRIEFLY OVER THE NW GULF WATERS TUE BEFORE GRADUALLY MOVING BACK INLAND THROUGH MID WEEK. STRONG WESTERLY AND NORTHWESTERLY FLOW ALOFT IS PRESENT ACROSS THE AREA. THESE WINDS ARE TRANSPORTING MID/UPPER LEVEL MOISTURE FROM THE EPAC REGION ACROSS N MEXICO INTO THE GULF WATERS MAINLY N OF 24N. AN UPPER-LEVEL RIDGE ANCHORED ON A HIGH OVER GUATEMALA DOMINATES THE SOUTH PORTION OF THE GULF AND SE MEXICO INCLUDING THE YUCATAN PENINSULA. STRONG UPPER LEVEL SUBSIDENCE AND IMPLIED DRY AIR MASS IS NOTED WITHIN THIS RIDGE. CARIBBEAN SEA... TWO WEAKENING SURFACE FRONTS EXTEND INTO THE CARIBBEAN SEA FROM THE W ATLC. THE LEAD FRONT IS STATIONARY AND EXTENDS FROM E CUBA TO E OF NICARAGUA NEAR 12N83W. AN AREA OF SCATTERED MODERATE CONVECTION IS NEAR THE TAIL END OF THIS FRONT AFFECTING FROM 10N-13N WEST OF 80W. THE SECONDARY FRONT IS OVER WESTERN CUBA. A RELATIVELY COOLER AND DRIER AIRMASS DOMINATES WEST AND CENTRAL CUBA...THE NW CARIBBEAN AND NORTHERN CENTRAL AMERICA WHERE BROKEN LOW TO MID CLOUDS WITH EMBEDDED LIGHT SHOWERS ARE NOTED. IN ADDITION...NLY WINDS OF 15 TO 25 KT ARE BLOWING W OF THE STATIONARY FRONT WITH THE STRONGEST WINDS NEAR THE COAST OF NICARAGUA. EASTERLY WINDS ARE EXPECTED TO INCREASE OVER MOST OF THE CARIBBEAN SEA AND THE TROPICAL N ATLC SUN AND MON AS HIGH PRES CURRENTLY OVER THE SE CONUS MOVES NE OVER THE W ATLC. AS IS TYPICAL FOR THIS TIME OF THE YEAR...FRAGMENTS OF LOW LEVEL MOISTURE ARE MOVING WWD ACROSS THE E AND CENTRAL CARIBBEAN UNDER AN ELY WIND FLOW. ALOFT...A RIDGE EXTENDS FROM N COLOMBIA TO GUATEMALA AND SE MEXICO. UPPER LEVEL DIFFLUENCE ASSOCIATED WITH THIS UPPER FEATURE IS HELPING TO INDUCE SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS THE SW CARIBBEAN INCLUDING ALSO COSTA RICA AND WESTERN PANAMA. ATLANTIC OCEAN... A DEEP LAYERED TROUGH OVER THE WESTERN ATLC SUPPORTS A COLD FRONT THAT CROSSES JUST E OF BERMUDAS AND ENTERS THE FORECAST AREA NEAR 31N65W. THIS FRONTAL ZONE CONTINUES SW ACROSS THE SE BAHAMAS AND EASTERN CUBA WHERE IT BECOMES STATIONARY CONTINUING OVER THE CARIBBEAN SEA. THE PORTION OF THE FRONT OVER THE CARIBBEAN SEA IS DISSIPATING...AND AS OF 2100 UTC A SURFACE TROUGH IS ANALYZED FROM E CUBA TO THE SW CARIBBEAN. A REINFORCING COLD FRONT...WHICH IS ALSO WEAKENING...IS WITHIN AROUND 120 NM BEHIND OF THE MAIN FRONT AND LIES OVER THE NW BAHAMAS AND WESTERN CUBA. A PRE-FRONTAL TROUGH WITH A BAND OF SCATTERED SHOWERS AND ISOLATED TSTMS REMAINS WITHIN AROUND 70 NM E OF THE PRIMARY FRONT N OF 23N. SFC HIGH PRES OVER THE SE CONUS EXTENDS A RIDGE OVER THE W ATLC BEHIND THE AFOREMENTIONED FRONTS. THIS SYSTEM WILL BE OFFSHORE THE CAROLINAS SUNDAY MORNING...AND WILL MOVE NE ACROSS THE OPEN OCEAN WATERS OF THE W AND CENTRAL ATLC SUNDAY THROUGH TUE. NE WINDS OF 20 TO 30 KT AROUND THIS HIGH ARE BRINGING ABUNDANT CLOUDINESS TO THE STATE OF FLORIDA AND THE NW BAHAMAS. THE REMAINDER OF THE DISCUSSION AREA IS UNDER THE INFLUENCE OF A STRONG SFC HIGH PRES SYSTEM FORECAST TO SHIFT SLIGHTLY EWD APPROACHING THE AZORES DURING THE NEXT 24 HOURS. SUBSIDENCE AROUND THIS 1040 MB SURFACE HIGH CENTERED NEAR 37N36W IS GENERALLY SUPPORTING FAIR WEATHER CONDITIONS ACROSS THE E ATLC. A SURFACE TROUGH HAS DEVELOPED OVER THE CENTRAL ATLC AND RUNS FROM 28N54W TO 24N52W TO 18N52W. A LARGE AREA OF SCATTERED MODERATE CONVECTION IS EAST OF THE TROUGH AXIS COVERING FROM 18N-30N BETWEEN 40W-52W...MORE CONCENTRATED N OF 25N AND WEST OF 48W. UPPER DIFFLUENCE AHEAD OF A SHARP UPPER-LEVEL TROUGH LOCATED IN THIS SAME AREA IS ENHANCING THIS CONVECTIVE ACTIVITY. MOST OF THE COMPUTER MODELS ANTICIPATE A SURFACE LOW DEVELOPING IN THE VICINITY OF THIS SFC TROUGH NEAR 26N56W LATE MONDAY NIGHT/EARLY TUE MORNING. WINDS WILL BE STRONGEST OVER THE W SEMICIRCLE OF THE DEVELOPING LOW DUE TO THE TIGHT PRES GRADIENT BETWEEN THIS LOW AND THE SFC HIGH PRES MOVING OFF THE SE CONUS. MAINLY WESTERLY ZONAL FLOW ALOFT DOMINATES THE DEEP TROPICS...WITH UPPER LEVEL DIFFLUENCE SUPPORTING THE CONVECTION IN THE VICINITY OF THE ITCZ. $$ GR