000 AXNT20 KNHC 130004 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT SUN OCT 12 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. ...SPECIAL FEATURES... A TROPICAL SYSTEM IN THE E ATLC HAS BEEN UPGRADED TO TROPICAL STORM NANA AT 12/2100 UTC. TROPICAL STORM NANA CENTERED NEAR 16.4N 37.9W OR ABOUT 805 NM W OF THE CAPE VERDE ISLANDS AT 12/2100 UTC. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1005 MB. MAXIMUM SUSTAINED WIND SPEED IS 35 KT WITH GUSTS TO 45 KT. PLEASE SEE LATEST NHC PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT4/WTNT34 KNHC AND THE FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS ON TROPICAL STORM NANA. TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 75 NM FROM THE CENTER. NUMEROUS MODERATE TO STRONG CONVECTION IS FROM 14N-19N BETWEEN 32W-37W. NANA IS EXPECTED TO WEAKEN DURING THE NEXT DAY OR SO...AND NANA IS FORECAST TO BECOME A TROPICAL DEPRESSION TONIGHT OR MONDAY. A 1006 MB SURFACE LOW IN THE E CARIBBEAN IS CENTERED NEAR 15N68W...OR ABOUT 175 NM SSW OF PUERTO RICO. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 12N-18N BETWEEN 63W-68W. THIS SYSTEM HAS THE POTENTIAL TO BECOME A TROPICAL DEPRESSION TOMORROW. ALSO...THIS SYSTEM IS EXPECTED TO RESULT IN HEAVY RAINS OVER PUERTO RICO AND PORTIONS OF THE LEEWARD ISLANDS OVER THE NEXT FEW DAYS. THESE RAINS COULD CAUSE FLASH FLOODS IN SOME AREAS. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 42W/43W S OF 20N MOVING W 10-15 KT. SATELLITE IMAGERY DEPICTS INVERTED-V PATTERN IN LOW LEVEL CLOUDS ALONG WAVE AXIS N OF 16N. SCATTERED MODERATE CONVECTION IS WITHIN 150 NM E OF WAVE AXIS S OF 14N...WHICH IS BEING ENHANCED BY A 1009 MB SURFACE LOW ON THE WAVE AXIS NEAR 12N43W. A TROPICAL WAVE IS ALONG 56W S OF 20N MOVING W NEAR 10 KT. A WEAK MAXIMUM IN DEEP LAYER MOISTURE COINCIDES WITH THIS WAVE AXIS FROM MIMIC TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. SURFACE OBSERVATIONS DEPICT WEAK COUNTERCLOCKWISE CURVATURE IN SURFACE WIND FIELD NEAR WAVE AXIS. ISOLATED SHOWERS ARE WITHIN 90 NM W OF WAVE AXIS N OF 18N. A TROPICAL WAVE IS IN THE CENTRAL CARIBBEAN ALONG 69W/70W S OF 20N...EXTENDING FROM E HISPANIOLA TO NW VENEZUELA...MOVING W NEAR 10 KT. WEAK COUNTERCLOCKWISE CURVATURE IS NOTED IN OBSERVED SURFACE WIND FIELD...AND WAVE COINCIDES WITH A WESTWARD-MOVING DEEP LAYER MOISTURE SURGE. SCATTERED MODERATE CONVECTION IS WITHIN 120 NM EITHER SIDE OF WAVE AXIS S OF 13N. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 9N15W 4N31W 10N48W 10N64W 9N80W. IN ADDITION TO CONVECTION ASSOCIATED WITH THE TROPICAL WAVES... ISOLATED MODERATE CONVECTION IS FROM 3N-10N BETWEEN 22W-31W. ISOLATED MODERATE CONVECTION IS WITHIN 180 NM EITHER SIDE OF THE AXIS BETWEEN 31W-36W. SIMILAR CONVECTION IS WITHIN 90 NM EITHER SIDE OF THE AXIS BETWEEN 47W-52W. ISOLATED MODERATE CONVECTION IS WITHIN 90 NM EITHER SIDE OF THE AXIS BETWEEN 70W-80W... AFFECTING N VENEZUELA...NW COLOMBIA...PANAMA...AND COSTA RICA. ...DISCUSSION... GULF OF MEXICO... AN UPPER HIGH IS CENTERED OVER S TEXAS NEAR 28N99W. DRY NORTHERLY UPPER FLOW E OF THE HIGH IS RESULTING IN SUBSIDENCE AND STABLE ATMOSPHERIC CONDITIONS ACROSS MUCH OF THE CENTRAL AND W GULF. SUBSIDENCE AROUND A SURFACE RIDGE EXTENDING INTO THE GULF FROM THE NE CONUS IS SUPPRESSING CONVECTION ACROSS MUCH OF THE GULF. HOWEVER...WEAK INSTABILITY AROUND AN UPPER LOW CENTERED IN THE SE GULF NEAR 20N86W AND ITS ASSOCIATED UPPER TROUGH IS CONTRIBUTING TO ISOLATED SHOWERS AND THUNDERSTORMS WITHIN 120 NM EITHER SIDE OF A LINE FROM 28N80W TO 18N90W... AFFECTING W CUBA...W FLORIDA...THE YUCATAN PENINSULA...AND THE ADJACENT GULF WATERS. CARIBBEAN SEA... A 1006 MB SURFACE LOW IS IN THE E CARIBBEAN. PLEASE SEE SPECIAL FEATURES SECTION ABOVE FOR MORE INFORMATION ON THIS FEATURE. MOIST SOUTHWESTERLY FLOW ALOFT IS E OF THE UPPER LOW IN THE SE GULF AND COVERS MUCH OF THE CENTRAL AND W CARIBBEAN. TO THE E...A WEAK UPPER RIDGE EXTENDS FROM N VENEZUELA TO PUERTO RICO. DEEP LAYER MOISTURE ACROSS THE CARIBBEAN IS RESULTING IN CLOUDINESS ACROSS MUCH OF THE CARIBBEAN. UPPER LEVEL DIVERGENCE OVER THE W CARIBBEAN IS SUPPORTING ISOLATED MODERATE CONVECTION W OF 79W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION THAT DEVELOPED OVER THE HIGHER TERRAIN OF NICARAGUA...COSTA RICA...E CUBA...HISPANIOLA...N COLOMBIA...AND N VENEZUELA THIS AFTERNOON IS IMPACTING THE NEARBY CARIBBEAN WATERS. ATLANTIC OCEAN... TROPICAL STORM NANA HAS FORMED IN THE E PACIFIC. PLEASE SEE SPECIAL FEATURES SECTION FOR MORE INFORMATION ON TROPICAL STORM NANA. OVER THE W ATLC...AN UPPER TROUGH AXIS EXTENDS FROM 30N79W TO CENTRAL FLORIDA NEAR 27N81W TO THE SE GULF. INSTABILITY WITH THIS FEATURE IS RESPONSIBLE FOR ISOLATED SHOWER AND THUNDERSTORM DEVELOPMENT N OF 27N W OF 77W. ALSO...A CLUSTER OF MODERATE CONVECTION IS FROM 26N-28N BETWEEN 73W-75W...WHICH IS BEING ENHANCED BY A FAST WESTWARD-MOVING LOW LEVEL CIRCULATION FEATURE KNOWN AS A SCREAMING EAGLE. THIS FEATURE IS EXPECTED TO REACH S FLORIDA BY 13/0600 UTC...BRINGING SCATTERED TO NUMEROUS SHOWERS TONIGHT TO S FLORIDA. FURTHER TO THE E...WEAK UPPER LEVEL DIFFLUENCE IS GENERATING SCATTERED MODERATE CONVECTION FROM 24N-26N BETWEEN 57W-60W. AN UPPER TROUGH IS N OF 24N BETWEEN 38W-45W...AND IS SUPPORTING A SURFACE STATIONARY FRONT THAT EXTENDS FROM 32N42W TO 29N45W TO 26N50W. DEEP LAYER DRY AIR IS INHIBITING CONVECTIVE DEVELOPMENT NEAR THIS FRONT. A WEAK UPPER RIDGE IS N OF 25N BETWEEN 32W-39W. A SURFACE RIDGE AXIS EXTENDS S OF A 1021 MB SURFACE HIGH NEAR 32N26W TO 11N24W...RESULTING IN MAINLY FAIR WEATHER N OF 10 N AND E OF 27W. OVER THE TROPICAL ATLC...A 1009 MB SURFACE LOW IS CENTERED NEAR 12N43W AND IS ENHANCING SCATTERED MODERATE CONVECTION WITHIN 150 NM E OF THE TROPICAL WAVE AXIS ALONG 42W/43W. AN UPPER RIDGE EXTENDS ALONG 10N BETWEEN AFRICA AND 49W. SPECIAL THANKS GO TO THE NATIONAL WEATHER SERVICE FORECAST OFFICE IN MIAMI FLORIDA FOR COORDINATION ON SCREAMING EAGLE FEATURE. $$ COHEN