000 AXNT20 KNHC 202350 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT THU SEP 20 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. ...SPECIAL FEATURES... TROPICAL STORM NADINE IS CENTERED NEAR X36.0 28.1W AT 21/0000 UTC OR ABOUT ABOUT 148 NM S OF PICO IN THE AZORES MOVING ESE AT 7 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 981 MB. MAXIMUM SUSTAINED WIND SPEED IS 45 KT WITH GUSTS TO 55 KT. SEE LATEST NHC INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT4/ WTNT34 AND THE FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS. SCATTERED MODERATE CONVECTION IS FROM 37N-39N BETWEEN 25W-30W. SCATTERED SHOWERS AND POSSIBLE ISOLATED THUNDERSTORMS COVER THE REMAINDER OF THE AREA FROM 35N-40N BETWEEN 22W-32W. A LARGE DEEP LAYERED LOW IS IN THE W/CENTRAL ATLC NEAR 32N55W SUPPORTING A 1006 MB SURFACE LOW NEAR 31N54W WITH A SURFACE TROUGH EXTENDING ALONG 29N53W TO 24N59W AND A SECOND 1010 MB LOW NEAR 32N53W. CONDITIONS APPEAR FAVORABLE FOR GRADUAL DEVELOPMENT OF THE 1006 MB LOW AS IT MOVES W TO WNW NEAR 9 KT OVER THE NEXT DAY OR SO. CONDITIONS APPEAR FAVORABLE FOR GRADUAL DEVELOPMENT DURING THE NEXT DAY OR SO BEFORE UPPER-LEVEL WINDS BECOME LESS CONDUCIVE ON SATURDAY. THIS SYSTEM HAS A HIGH CHANCE OF BECOMING A SUBTROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES WNW NEAR 9 KT. CLUSTERS OF SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ARE N OF 26N BETWEEN 45W-59W AND FROM 21N-26N BETWEEN 48W-54W. ...TROPICAL WAVES... TROPICAL WAVE W OF THE CAPE VERDE ISLANDS EXTENDS FROM 20N33W ALONG 15N34W TO 11N35W MOVING W 20-25 KT. WAVE IS EMBEDDED WITHIN A SURGE OF DEEP MOISTURE WITH A SWATH OF DRY AIR UNDER CUTTING THE MOISTURE ALONG 13N AS DEPICTED ON TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 30 NM OF LINE FROM 13N38W TO 16N37W. TROPICAL WAVE E OF THE LESSER ANTILLES EXTENDS FROM 20N52W TO 13N57W MOVING W NEAR 15 KT. WAVE IS EMBEDDED WITHIN AN ISOLATED SURGE OF DEEP MOISTURE AS DEPICTED ON TOTAL PRECIPITABLE WATER IMAGERY. ISOLATED SHOWERS/THUNDERSTORMS ARE WITHIN 120 NM EITHER SIDE OF THE WAVE AXIS. TROPICAL WAVE IN THE CARIBBEAN EXTENDS 22N78W TO 14N81W MOVING W 10-15 KT. WAVE IS EMBEDDED WITHIN A BROAD AREA OF DEEP MOISTURE THAT COVERS THE ENTIRE CARIBBEAN AS DEPICTED ON TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED SHOWERS/THUNDERSTORMS ARE WITHIN 240 NM W OF THE WAVE AXIS. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS ACROSS W AFRICA INTO THE E TROPICAL ATLC NEAR 14N16W CONTINUING ALONG 9N23W TO 7N37W WHERE THE ITCZ CONTINUES ALONG 6N45W INTO SOUTH AMERICA NEAR 4N53W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 60/75 NM OF LINE FROM 9N16W TO 12N19W. CLUSTERS OF SCATTERED MODERATE CONVECTION ARE FROM 5N-8N BETWEEN 17W-44W. ...DISCUSSION... GULF OF MEXICO... BROAD UPPER TROUGH REMAINS OVER THE E CONUS INTO THE GULF N OF 20N SUPPORTING A STATIONARY FRONT THAT AT 20/2100 UTC EXTENDS FROM THE W ATLC ACROSS FLORIDA INTO THE GULF NEAR FORT MYERS ALONG 26N86W TO 26N91W THEN S INTO THE BAY OF CAMPECHE TO NEAR 19N93W. CLUSTERS OF SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ARE WITHIN 120/150 NM N OF THE FRONT E OF 91W AND S OF THE FRONT TO OVER FLORIDA...CUBA...AND THE YUCATAN PENINSULA. AN UPPER RIDGE COVERS THE FAR S GULF WITH THE RIDGE AXIS OVER S MEXICO ENHANCING ISOLATED SHOWERS/THUNDERSTORMS WITHIN 60 NM ALONG THE COAST OF S MEXICO IN THE BAY OF CAMPECHE. THIS IS LEAVING W GULF UNDER MOSTLY FAIR WEATHER THIS EVENING. THE STATIONARY FRONT WILL WEAKEN THROUGH FRI THEN DISSIPATE SAT. HIGH PRESSURE WILL BUILD S FRI THROUGH MON. CARIBBEAN SEA... THE UPPER TROUGH OVER THE GULF OF MEXICO COMBINED WITH AN UPPER RIDGE THAT IS ANCHORED IN THE E PACIFIC REGION EXTENDING AN AXIS ACROSS S MEXICO INTO THE CARIBBEAN ACROSS S BELIZE TO 17N83W TO PROVIDE DIFFLUENCE ALOFT TO GENERATE SCATTERED SHOWERS/ISOLATED THUNDERSTORMS N OF 20N TO OVER CUBA W OF 81W. AN UPPER RIDGE IS ANCHORED NEAR THE BAHAMA ISLANDS COVERS THE CENTRAL CARIBBEAN BETWEEN 70W-79W. DIFFLUENCE ALOFT IS GENERATING SCATTERED SHOWERS/ISOLATED THUNDERSTORMS N OF 17N TO OVER CUBA BETWEEN 75W-80W INCLUDING JAMAICA. THESE UPPER RIDGES ARE INDUCING AN INVERTED UPPER TROUGH S OF 17N TO OVER PANAMA AND COSTA RICA BETWEEN 79W-83W. AN UPPER LOW IS E OF THE LESSER ANTILLES NEAR 15N59W COVERING THE E CARIBBEAN E OF 70W GENERATING ISOLATED SHOWERS AND POSSIBLE ISOLATED THUNDERSTORMS N OF 15N E OF 67W ACROSS THE LEEWARD ISLANDS. THE MONSOON TROUGH EXTENDS ACROSS THE SW CARIBBEAN S OF 10N FROM COLOMBIA INTO THE E PACIFIC REGION OVER PANAMA/COSTA RICA GENERATING CLUSTERS OF SCATTERED SHOWERS/ISOLATED THUNDERSTORMS S OF 12N BETWEEN 75W-81W. HIGH PRESSURE WILL BUILD OFF OF THE SE COAST OF THE U.S. THROUGH MON. TROPICAL WAVE WILL REACH THE YUCATAN PENINSULA SAT. THE SECOND TROPICAL WAVE E OF THE LESSER ANTILLES WILL MOVE WNW INTO THE CARIBBEAN FRI THROUGH SAT AND INTO THE N CENTRAL CARIBBEAN SAT NIGHT. ATLANTIC OCEAN... THE UPPER TROUGH THAT COVERS THE E CONUS AND GULF OF MEXICO EXTENDS OVER THE NW ATLC SUPPORTING A STATIONARY FRONT THAT AT 20/2100 UTC ENTERS THE DISCUSSION AREA NEAR 32N72W EXTENDING ALONG 28N77W TO OVER THE FLORIDA PENINSULA NEAR MELBOURNE TO FORT MYERS BEFORE ENTERING THE GULF OF MEXICO. SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ARE N OF THE FRONT W OF 78W... OVER THE FLORIDA PENINSULA...AND S OF 27N W OF 76W TO OVER CUBA AND THROUGH THE STRAITS OF FLORIDA. AN UPPER RIDGE IS ANCHORED NEAR THE BAHAMA ISLANDS NEAR 24N73W EXTENDING S OVER THE CARIBBEAN AND N TO BEYOND 32N68W PROVIDING DIFFLUENCE ALOFT TO GENERATE SCATTERED SHOWERS/ISOLATED THUNDERSTORMS WITHIN 30 NM OF LINE FROM 25N73W TO BEYOND 32N70W. A DEEP LAYERED LOW IS TO THE E...SEE SPECIAL FEATURES ABOVE. AN UPPER LOW E OF THE LESSER ANTILLES IS ENHANCING THE ACTIVITY ASSOCIATED WITH THE TROPICAL WAVE E OF THE LESSER ANTILLES...SEE ABOVE. A 1018 MB HIGH IS SW OF T.S. NADINE NEAR 25N39W. THE STATIONARY FRONT WILL GRADUALLY DISSIPATE THROUGH FRI. HIGH PRESSURE WILL BUILD S FRI THROUGH MON. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ PAW