000 AXNT20 KNHC 182347 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 705 PM EST SUN NOV 18 2012 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...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS. BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS ACROSS WEST AFRICA TO THE COAST OF GUINEA-BISSAU AT 12N16W TO 8N21W. THE ITCZ BEGINS AT 8N21W AND CONTINUES ALONG 6N29W 8N43W 8N59W. SCATTERED MODERATE CONVECTION IS FROM 5N-7N BETWEEN 15W-17W. ISOLATED MODERATE/STRONG CONVECTION IS FROM 5N-8N BETWEEN 28W-31W. ...DISCUSSION... GULF OF MEXICO... MAINLY NORTHWESTERLY FLOW ALOFT CONTINUES TO COVER THE GULF OF MEXICO BETWEEN AN UPPER LEVEL RIDGE WITH AXIS FROM THE SW GULF NEAR 20N96W TO THE MISSISSIPPI VALLEY...AND AN UPPER LEVEL TROUGH EXTENDING FROM THE MID-ATLANTIC STATES THROUGH THE FLORIDA PENINSULA INTO THE NW CARIBBEAN. WATER VAPOR IMAGERY INDICATES MOSTLY DRY AIR IS BEING DRAWN OVER THE BASIN IN THE UPPER LEVELS. THIS...ALONG WITH SURFACE RIDGING ACROSS THE WESTERN GULF IS HELPING PROVIDING MOSTLY FAIR CONDITIONS AT THE SURFACE. HOWEVER...A SURFACE TROUGH EXTENDS FROM THE CENTRAL GULF INTO THE SE GULF ALONG 27N89W TO 20N84W. ISOLATED SHOWERS ARE WITHIN 150 NM TO EITHER SIDE OF THE AXIS. CYCLONIC WINDS OF 15-20 KT ARE ACROSS THE EASTERN GULF AROUND THE SURFACE TROUGH. ISOLATED SHOWERS ARE ALSO NOTED IN THE EXTREME SW GULF NEAR THE COAST OF MEXICO. THE SURFACE TROUGH IS EXPECTED TO DRIFT WEST SLOWLY OVER THE NEXT FEW DAYS WITH SURFACE RIDGING REMAINING ELSEWHERE. MOISTURE AND POSSIBLE SHOWERS WILL ACCOMPANY THE TROUGH. CARIBBEAN SEA... THE UPPER LEVEL TROUGH OVER THE FAR EASTERN GULF CONTINUES SOUTH INTO THE NW CARIBBEAN ACCOMPANIED BY DRY AIR ALOFT...WHICH IS PROVIDING MOSTLY FAIR CONDITIONS ACROSS THIS PORTION OF THE BASIN. A FEW ISOLATED SHOWERS ARE JUST EAST OF THE YUCATAN PENINSULA ASSOCIATED WITH A SURFACE TROUGH THAT EXTENDS THROUGH THE YUCATAN CHANNEL TO NEAR 20N84W. MOIST SOUTHWESTERLY FLOW AND DIFFLUENCE ALOFT BETWEEN THE UPPER TROUGH AND AN UPPER LEVEL RIDGE OVER THE EASTERN CARIBBEAN ALONG 66W ARE GENERATING A LARGE AREA OF SHOWERS/ISOLATED THUNDERSTORMS OVER THE CENTRAL CARIBBEAN FROM 11N-15N BETWEEN 77W-83W...AND FROM 14N-17N BETWEEN 70W-77W. A FEW SHOWERS/THUNDERSTORMS ARE ALSO TO THE NORTH OVER HISPANIOLA AND PUERTO RICO. SOME OF THE ACTIVITY IN THE SW CARIBBEAN IS ASSOCIATED WITH THE MONSOON TROUGH THAT EXTENDS THROUGH SOUTHERN COSTA RICA TO A 1010 MB SURFACE LOW NORTH OF PANAMA NEAR 10N78W. A CLUSTER OF SHOWERS/THUNDERSTORMS IS SOUTH OF THE LOW CENTER INTO COASTAL PANAMA. THE REMAINDER OF THE EASTERN CARIBBEAN IS UNDER FAIR CONDITIONS ASSOCIATED WITH DRY AIR ALOFT AROUND THE UPPER RIDGE. EXPECT LITTLE CHANGE OVER THE NEXT COUPLE OF DAYS. ATLANTIC OCEAN... AN UPPER LEVEL LOW JUST OFFSHORE OF SOUTH CAROLINA SUPPORTS A WEAK 1015 MB SURFACE LOW NEAR 32N79W FROM WHICH A STATIONARY FRONT EXTENDS SOUTH ALONG 30N77W 27N78W. CURRENTLY...NO SHOWERS ARE ASSOCIATED WITH THE FRONT IN THE DISCUSSION AREA. HOWEVER...A FEW SHOWERS ARE SOUTH OF THE BOUNDARY JUST OFF THE SE COAST OF FLORIDA. FARTHER EAST...DIFFLUENCE ALOFT BETWEEN THE UPPER LOW/TROUGH AND AN UPPER LEVEL RIDGE EXTENDING FROM THE EASTERN CARIBBEAN INTO THE THE CENTRAL ATLC IS HELPING SUPPORT SCATTERED SHOWERS/ISOLATED THUNDERSTORMS NORTH OF 289N BETWEEN 67W-71W...AND FROM 21N-24N BETWEEN 61W-65W. ISOLATED SHOWERS ARE POSSIBLE ELSEWHERE NORTH OF 21N BETWEEN 54W-68W. A PAIR OF SURFACE TROUGHS ARE EMBEDDED WITHIN THIS LARGE ARE OF DIFFLUENCE ALOFT. THE FIRST IS ALONG 28N69W TO 21N70W WITH ONLY THE AREA OF SHOWERS/THUNDERSTORMS TO THE NORTH AS PREVIOUSLY DESCRIBED. THE SECOND IS ALONG 31N59W TO 28N64W. DUE TO DENSE HIGH LEVEL CLOUDS...IT IS DIFFICULT TO TELL IF ANY SHOWERS ARE NEAR THE AXIS AT THE SURFACE. THE UPPER LEVEL RIDGE ACROSS THE CENTRAL ATLC CONTINUES TOWARDS THE NE WHERE IT BECOMES FLATTENED BY A LARGE LONGWAVE UPPER TROUGH OVER THE NORTHERN ATLC. THE RIDGE STILL SUPPORTS A BROAD SURFACE RIDGE ACROSS THE SE ATLC ANCHORED BY A PAIR OF 1022 AND 1023 MB HIGH CENTERS NEAR 31N39W AND 32N27W RESPECTIVELY. AN UPPER LEVEL LOW NEAR 17N43W...JUST EAST OF THE MAIN UPPER RIDGE...SUPPORTS A SURFACE TROUGH THAT EXTENDS INTO THE SURFACE RIDGE ALONG 18N40W TO 12N44W. SCATTERED SHOWERS/POSSIBLE THUNDERSTORMS ARE FROM 14N-23N BETWEEN 30W-40W. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ WALTON