000 AXNT20 KNHC 200512 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 105 AM EST THU NOV 20 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0445 UTC. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 54W S OF 15N MOVING W NEAR 15 KT. A MAXIMUM IN DEEP LAYER MOISTURE COINCIDES WITH THIS WAVE BASED ON TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. SATELLITE IMAGERY INDICATES AN INVERTED-V PATTERN TO THE CLOUD COVERAGE IN THE VICINITY OF THIS WAVE. SCATTERED MODERATE CONVECTION IS E OF THE WAVE AXIS FROM 9N-12N BETWEEN 51W-53W. THE TROPICAL WAVE THAT WAS PREVIOUSLY ALONG 76W S OF 17N FOR THE 19/1800 UTC SURFACE ANALYSIS HAS BEEN REMOVED FOR THE 20/0000 UTC SURFACE ANALYSIS. NE LOW LEVEL FLOW ACROSS THE W AND CENTRAL CARIBBEAN SEA HAS OVERTAKEN THIS FORMER WAVE TO THE E OF A SURFACE STATIONARY FRONT THAT EXTENDS FROM NE OF JAMAICA NEAR 18N76W TO 14N81W TO N OF COSTA RICA NEAR 9N82W. ...THE ITCZ... THE ITCZ AXIS IS ANALYZED ALONG 11N14W 8N22W 6N36W 7N44W 7N53W. SCATTERED MODERATE CONVECTION IS WITHIN 180 NM S OF THE ITCZ AXIS BETWEEN 21W-33W. SCATTERED MODERATE CONVECTION IS FROM 7N-10N BETWEEN 36W-41W. SIMILAR CONVECTION IS FROM 10N-16N BETWEEN 43W-48W. ...DISCUSSION... GULF OF MEXICO... STRONG WESTERLY FLOW ALOFT AND DEEP LAYER DRY AIR ARE PRESENT OVER MUCH OF THE GULF REGION. HOWEVER...UPPER LEVEL MOISTURE IS STREAMING FROM THE E PACIFIC REGION TO THE W GULF. ALSO...A MODIFIED CONTINENTAL POLAR AIRMASS PERSISTS ACROSS THE GULF REGION. AS A RESULT...TEMPERATURES ACROSS THE GULF REGION ARE BELOW SEASONAL AVERAGES. FREEZE WARNINGS ARE IN EFFECT FOR TONIGHT THROUGH THURSDAY MORNING FOR PORTIONS OF FLORIDA. THIS RELATIVELY COOLER AND DRIER AIRMASS IS BEING SUPPORTED BY A 1025 MB SURFACE HIGH S OF MOBILE ALABAMA NEAR 30N88W...WITH AN ASSOCIATED SURFACE RIDGE AFFECTING MUCH OF THE GULF REGION. AS THE COOLER AIR IS BEING ADVECTED OVER THE RELATIVELY WARMER GULF WATERS...WEAK LOW LEVEL INSTABILITY IS SUPPORTING SCATTERED STRATOCUMULUS CLOUDS ACROSS THE GULF MAINLY S OF 25N. HOWEVER...SUBSIDENCE AND STABLE ATMOSPHERIC CONDITIONS HIGHER IN THE ATMOSPHERE ARE INHIBITING DEEP CONVECTION ACROSS THE GULF REGION. OVER THE NEXT DAY...ANOTHER SURFACE COLD FRONT... CURRENTLY EXTENDING FROM THE GREAT LAKES TO THE PLAINS OF THE CONUS TO THE NORTHERN ROCKY MOUNTAINS...WILL MOVE SOUTHWARD AND APPROACH THE N GULF COAST. THIS COLD FRONT WILL REINFORCE THE MODIFIED CONTINENTAL POLAR AIRMASS ALREADY IN PLACE ACROSS THE GULF 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. CARIBBEAN SEA... ACROSS THE W CARIBBEAN...A SURFACE COLD FRONT EXTENDS FROM W HAITI NEAR 20N72W TO NE OF JAMAICA NEAR 18N76W...WITH A SURFACE STATIONARY FRONT EXTENDING FROM 18N76W TO 14N81W TO N OF COSTA RICA NEAR 9N82W. LOW LEVEL CONVERGENCE NEAR THESE FRONTS IS INTERACTING WITH DEEP MOISTURE OVER THE SW CARIBBEAN TO GENERATE SCATTERED SHOWERS AND THUNDERSTORMS OVER THE SW CARIBBEAN S OF 14N W OF 76W...INCLUDING ADJACENT PORTIONS OF COLOMBIA... PANAMA...AND COSTA RICA. THIS ACTIVITY IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE IN THE VICINITY OF AN UPPER RIDGE PRESENT OVER THE W CARIBBEAN...WITH THE AXIS OF THIS UPPER RIDGE EXTENDING FROM N COLOMBIA NEAR 11N74W TO 14N79W TO 17N83W. ALSO...A DISSIPATING SURFACE COLD FRONT OVER THE NW CARIBBEAN EXTENDS FROM 18N80W TO 20N85W TO THE YUCATAN PENINSULA NEAR 21N88W...WITH DEEP LAYER DRY AIR INHIBITING DEEP CONVECTION IN THE VICINITY OF THIS FRONT. OVER THE E CARIBBEAN...AN UPPER LEVEL RIDGE AXIS EXTENDS FROM NE VENEZUELA NEAR 10N66W TO 16N64W TO 14N63W...WITH UPPER LEVEL DIVERGENCE SUPPORTING SCATTERED SHOWERS OVER THE E CARIBBEAN S OF 15N E OF 69W. ATLANTIC OCEAN... A VIGOROUS UPPER TROUGH IS OVER THE W ATLC...WHICH IS SUPPORTING A SURFACE COLD FRONT THAT EXTENDS FROM W HAITI NEAR 20N72W TO 26N63W TO 32N57W AND EXTENDS TO THE N OF THE DISCUSSION AREA. ISOLATED SHOWERS ARE WITHIN 60 NM W AND 120 NM E OF THIS COLD FRONT. TO THE W OF THIS COLD FRONT...A MODIFIED CONTINENTAL POLAR AIRMASS IS IN PLACE...WITH TEMPERATURES BELOW SEASONAL AVERAGES ACROSS FLORIDA AND SCATTERED STRATOCUMULUS CLOUDS BETWEEN THIS FRONT AND THE COAST OF THE SE CONUS. IN THE WAKE OF THE COLD FRONT...GALE FORCE WINDS ARE OCCURRING WITHIN 45 TO 60 NM OF A LINE FROM 16N95W TO 13N97W...WHERE N TO NE SURFACE WINDS OF 30 TO 45 KT ARE OCCURRING. FARTHER TO THE E...A 1011 MB SURFACE LOW IS CENTERED NEAR 28N45W. DEEP LAYER DRY AIR IS INHIBITING DEEP CONVECTION NEAR THIS SURFACE LOW. ALSO...A SURFACE RIDGE IS N OF 19N BETWEEN 18W-33W...RESULTING IN FAIR WEATHER CONDITIONS ACROSS THE E ATLC. $$ COHEN