000 AXNT20 KNHC 181805 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT SAT AUG 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1700 UTC. ...SPECIAL FEATURES... HELENE HAS MOVED INLAND THIS MORNING AND WAS CENTERED NEAR 22.0N 98.5W AT 18/1500 UTC...OR ABOUT 15 MI SSW OF TAMPICO MEXICO... MOVING NW AT 8 KT. WINDS ASSOCIATED WITH HELENE HAVE DIMINISHED AND...THE SYSTEM HAS BEEN DOWNGRADED TO A TROPICAL DEPRESSION. MAXIMUM SUSTAINED WIND SPEED IS 30 KT WITH GUSTS TO 40 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1008 MB. THE BROAD CYCLONIC CIRCULATION ASSOCIATED WITH HELENE CONTINUES TO DOMINATE MUCH OF THE SW GULF S OF 25N AND W OF 93W...WITH ABUNDANT TROPICAL MOISTURE. SCATTERED TO LOCALLY NUMEROUS SHOWERS AND TSTMS ARE OCCURRING WITHIN 270 NM ACROSS THE EASTERN SEMICIRCLE OF THE CENTER OF HELENE...MAINLY OVER WATER. SEE LATEST NHC INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT2/WTNT32 KNHC AND THE FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. THE CIRCULATION ASSOCIATED WITH HELENE IS EXPECTED TO DRIFT W AND NW OVER THE NEXT FEW DAYS AND WEAKEN...AND INTERACT WITH SIERRA MADRE ORIENTALES OF MEXICO TO PRODUCE SIGNIFICANT RAINFALL... WITH THE POTENTIAL FOR WIDESPREAD HEAVY RAINS...LEADING TO AREAS OF FLASH FLOODING AND MUDSLIDES. HURRICANE GORDON WAS LOCATED NEAR 34.1N 38.6W AT 18/1500...OR ABOUT 610 NM WSW OF THE AZORES...MOVING E AT 16 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 983 MB. MAXIMUM SUSTAINED WIND SPEED HAVE INCREASED TO 70 KT WITH GUSTS TO 85 KT. SATELLITE IMAGERY THIS MORNING SHOWED A 20 NM WELL DEFINED EYE WITH GORDON. NEARLY SOLID BANDS WITH NUMEROUS STRONG TSTMS WERE OCCURRING WITHIN 75 NM OF THE CENTER OF GORDON WITH SCATTERED MODERATE CONVECTION ELSEWHERE WITHIN 150 NM OF CENTER. SEE LATEST NHC INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT3/WTNT33 AND THE FULL FORECAST/ ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS. THERE IS SOME OPPORTUNITY FOR GORDON TO STRENGTHEN SLIGHTLY IN THE NEXT 12 TO 18 HOURS BEFORE INCREASING WIND SHEAR AND COOLER SST'S CAUSE A STEADY WEAKENING TREND. THE GOVERNMENT OF PORTUGAL HAS ISSUED A HURRICANE WARNING FOR THE CENTRAL AND EASTERN AZORES. A VIGOROUS TROPICAL WAVE IS LOCATED IN THE ERN ATLC ALONG 27W...WITH A ASSOCIATED 1008 MB LOW NEAR 14N27W EMBEDDED WITHIN THE MONSOON TROUGH. THIS WAVE IS RACING WESTWARD AROUND 20 KT...AND IS NOW FORECAST BY THE GLOBAL MODELS TO MAINTAIN THIS FAST MOTION ACROSS THE ATLC DURING THE NEXT SEVERAL DAYS. SCATTERED SHOWERS AND THUNDERSTORMS WERE OCCURRING ARE FROM 11N-16N BETWEEN 27W-31W. CONDITIONS APPEAR CONDUCIVE FOR GRADUAL DEVELOPMENT DURING THE NEXT FEW DAYS...AND THIS SYSTEM HAS A MEDIUM CHANCE OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS. GLOBAL MODELS HAS CHANGED SIGNIFICANTLY IN THE FORECAST OF THIS WAVE DURING THE PAST 2 DAYS...AND A MORE WWD TRAJECTORY INTO THE CARIBBEAN IS NOW SUGGESTED BY THE OPERATIONAL MODELS AS WELL AS THE ENSEMBLE MEANS. INTERESTS ACROSS THE E AND NE CARIBBEAN SHOULD MONITOR THE PROGRESS OF THIS SYSTEM AS IT TREKS ACROSS THE ATLC. ...TROPICAL WAVES... A TROPICAL WAVE WAS LOCATED ACROSS THE CENTRAL TROPICAL ATLC ALONG 41W-42W...WITH AN ASSOCIATED 1013 MB LOW NEAR 11N41W EMBEDDED WITHIN THE MONSOON TROUGH. THIS WAVE IS MOVING W AT 15-20 KT. SAHARAN AIR CONTINUES TO DOMINATE THIS WAVE AND LIMIT CONVECTION...WITH SCATTERED MODERATE TO STRONG CONVECTION OCCURRING ACROSS SRN PORTIONS OF THE LOW...S OF THE MONSOON TROUGH...AND WELL TO THE NW...FROM 12N TO 15N BETWEEN 42W AND 47W...WHERE NELY FLOW IS CONVERGING. THIS WAVE...AND THE WAVE MENTIONED ABOVE ALONG 27W...ARE EMBEDDED WITHIN AN ELONGATED MONSOONAL CIRCULATION THAT EXTENDS FROM THE W COAST OF AFRICA TO NEAR 50W. A CARIBBEAN TROPICAL WAVE WAS ALONG ABOUT 70W RACING WWD NEAR 20 KT...WITH SCATTERED MODERATE ISOLATED STRONG CONVECTION OCCURRING FROM 15N ACROSS HISPANIOLA AND INTO THE ATLC TO 23N...MAINLY BEHIND THE WAVE AXIS BETWEEN 70W AND 67W. ALTHOUGH THIS WAVE HAS BEEN ACCOMPANIED BY A LARGE AREA OF SAL AS IT HAS MOVED ACROSS THE ATLC...IT REMAINS VERY ENERGETIC...WITH THE 1200 UTC SAN JUAN UPPER AIR SOUNDING SHOWING SELY WINDS 25-30 KT IN LAYER FROM JUST ABOVE THE SURFACE TO 1200 FT AGL. THIS WAVE IS REACHING THE W PERIPHERY OF THE ATLC RIDGE AND WILL BEGIN TO MOVE MORE WNW THE NEXT FEW DAYS...AND IGNITE WIDELY SCATTERED MODERATE TO STRONG CONVECTION ACROSS THE N CENTRAL CARIBBEAN AND GREATER ANTILLES...WITH SAL CONTRIBUTING TO SQUALLS AND STRONG WIND GUSTS. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXITS THE W AFRICAN COAST NEAR 15N17W...WHERE THE NEXT TROPICAL WAVE APPEARS POISED TO EXIT THE AFRICAN CONTINENT THIS AFTERNOON...AND MEANDERS WWD TO LOW PRES 1008 MB NEAR 14N27W...THEN CONTINUES WSW TO LOW PRES NEAR 11N42W...THEN CONTINUES ON TO 09N52W...WHERE IT TRANSITIONS TO ITCZ...CONTINUING ON TO 08N59W TO 11N67W. CONVECTION ASSOCIATED WITH THE TROUGH IS ADEQUATELY DESCRIBED ABOVE WITH EACH OF THE TROPICAL WAVES. SCATTERED MODERATE TO STRONG CONVECTION ASSOCIATED WITH THE WAVE ALONG THE W COAST OF AFRICA WAS OCCURRING FROM 11N-15N E OF 21W. SCATTERED MODERATE TO STRONG CONVECTION ASSOCIATED WITH THE ITCZ WAS OCCURRING ALONG COASTAL SECTIONS OF GUYANA AND VENEZUELA BETWEEN 59W AND 66W. ...DISCUSSION... GULF OF MEXICO... WEAK SURFACE RIDGING EXTENDS FROM THE W ATLC ACROSS SRN FLORIDA AND INTO THE CENTRAL GULF...THEN NW INTO THE NW GULF...AS HELENE SLOWLY DRIFTS FURTHER INLAND ACROSS MEXICO. A WEAK SURFACE TROUGH WAS BEGIN DRAGGED EWD ACROSS N CENTRAL FLORIDA...YIELDING MOISTURE CONVERGENCE TO ITS S ACROSS CENTRAL PORTIONS OF THE STATE WITH SCATTERED MODERATE CONVECTION. A WEAK COLD FRONT WAS SINKING SWD ACROSS THE N GULF STATES WITH NUMEROUS MODERATE TO STRONG CONVECTION ERUPTING ACROSS S LOUISIANA AND THE NEARSHORE COASTAL WATERS...AND IS EXPECTED TO SHIFT SLOWLY ESE THIS AFTERNOON. BROAD UPPER TROUGHING ACROSS THE E TWO-THIRDS OF THE US.S WILL MAINTAIN MILD W TO NW FLOW ALOFT ACROSS THE N AND NE GULF AND YIELD UNSTABLE CONDITIONS...AND THUS ACTIVE CONVECTION IS EXPECTED THERE THROUGH THIS EVENING. ACROSS THE SW AND S CENTRAL GULF...MOIST AND UNSTABLE SELY FLOW CONTINUES TO SPREAD MOISTURE TOWARDS TEXAS AND THE MEXICAN OFFSHORE WATERS. SE WINDS 15-20 KT WITH SEAS 6-7 FT ARE LIKELY TO CONTINUE ACROSS THIS REGION THROUGHOUT THE DAY. CARIBBEAN SEA... SCATTERED TO NUMEROUS MODERATE TO STRONG CONVECTION WAS SHIFTING W ACROSS THE SW CARIBBEAN S OF 12.5W AND W OF 76W...AND APPEARS TO BE ASSOCIATED WITH A WEAK PERTURBATION ALONG THE MONSOON TROUGH INTERACTING WITH DIVERGENT UPPER SW FLOW. SKIES WERE GENERALLY CLEAR ACROSS THE REMAINDER OF THE BASIN W OF THE TROPICAL WAVE ALONG 70W...WITH SPOTTY CONVECTION S OF CUBA. ITCZ RELATED MOISTURE IS BEGIN DRAGGED WWD ACROSS VENEZUELA BEHIND THE TROPICAL WAVE ALONG 70W...AND SAL AND VERY STABLE AIR FOLLOWING THIS WAVE AND MOVING INTO THE E CARIB ATTM. SQUALLS AND TSTMS ASSOCIATED WITH THIS WAVE WILL EXT THE WATERS OF THE MONA PASSAGE LATER THIS AFTERNOON AND CONTINUE TO AFFECT HISPANIOLA AND THE ADJACENT WATERS. FRESH SE WINDS AROUND 20 KT WILL OCCUR WITH AND BEHIND THIS WAVE...MAINLY N OF 15N...WITH SEAS 5-7 FT. OTHERWISE MODERATE TRADEWINDS PREVAIL ACROSS THE BASIN. ATLANTIC OCEAN... WATER VAPOR SHOWS A VERY BROAD UPPER LEVEL TROUGH ACROSS THE E TWO-THIRDS OF THE U.S. SHIFTING SLOWLY E OFF THE ERN SEABOARD. CONVERGENCE LINES BETWEEN BERMUDA AND THE SE U.S. COAST ARE RESPONDING FAVORABLE TO THIS UNSTABLE ENVIRONMENT TO YIELD BROKEN LINES OF WIDELY SCATTERED SHOWERS AND TSTMS. A TUTT STRETCHED SW TO NE FROM HISPANIOLA TO THE CENTRAL ATLC AND IS PRODUCING A GENERALLY STABLE ATMOSPHERE N OF 20N E OF 60W. SAL ASSOCIATED WITH THE THREE TROPICAL WAVES DISCUSSED ABOVE IS SPREAD ACROSS MUCH OF THE TROPICAL AND SUBTROPICAL ATLC FROM NW AFRICA W-SW INTO THE ERN CARIB...AND IS MOST DENSE N OF THE WAVES...N OF 16N. GOES-R PRODUCTS CLEARLY SHOW THIS SAL...WITH A VERY NARROW BREAK N OF 16N ALONG 42-43W. A THERMAL LOW PRES CENTER ALONG THE W COAST OF AFRICA NEAR 20N17W CONTINUES TO ENTRAIN DENSE AFRICAN DUST THAT STRETCHES N-NE ALONG THE COAST AND INTO SW PORTIONS OF SPAIN. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ STRIPLING