000 AXNT20 KNHC 192346 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT THU JUL 19 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 2245 UTC. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 17N39W TO 9N46W MOVING W NEAR 20 KT. WAVE WAS ALIGNED WITH A TILT TO BETTER FIT THE SHAPE OF A BROAD SURGE OF DEEP LAYER MOISTURE THAT TRAILS THE WAVE SEEN IN TOTAL PRECIPITABLE IMAGERY. DUE TO THE LARGE AREA OF SAHARAN DUST COVERING THE TROPICAL ATLC...NO DEEP CONVECTION IS ASSOCIATED WITH THE WAVE EXCEPT FOR A SMALL AREA OF MODERATE CONVECTION FROM 7N-8N BETWEEN 47W-49W. TROPICAL WAVE IS MOVING THROUGH THE ERN CARIBBEAN ALONG 20N67W TO 12N63W. THE WAVE LIES ON THE W SIDE OF A TILTED SURGE OF DEEP LAYER MOISTURE PRESENT IN TOTAL PRECIPITABLE WATER IMAGERY...WHICH EXPLAINS THE TILT OF THE WAVE. ISOLATED MODERATE CONVECTION IS WITHIN 200 NM E AND 150 NM W OF THE AXIS. A LARGE AREA OF SAHARAN DUST IS IMMEDIATELY E OF THE WAVE. THIS WAVE IS APPROACHING AN UPPER LEVEL LOW NEAR ERN CUBA. SHOWER ACTIVITY SHOULD INCREASE NEAR THE WAVE AS IT APPROACHES THE ERN AND DIFFLUENT SIDE OF THE UPPER LOW. TROPICAL WAVE IS MOVING THROUGH THE BAY OF CAMPECHE ALONG 23N94W TO 17N93W MOVING W NEAR 15-20 KT. THE WAVE IS ON THE E SIDE OF AN AREA OF ENHANCED DEEP LAYER MOISTURE THAT COVERS THE FAR WRN GULF OF MEXICO. HOWEVER...IT LIES ON THE WRN SIDE OF AN UPPER LEVEL LOW WHICH IS DRAWING DRY AIR ALOFT OVER THE WAVE. THIS IS PREVENTING CONVECTION NEAR THE AXIS. THERE ARE AREAS REMOVED FROM THE WAVE TO EITHER SIDE...BUT ARE LIKELY TIED TO THE UPPER LOW AND A SECOND UPPER LOW OVER N CENTRAL MEXICO. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS ACROSS W AFRICA TO THE COAST OF GUINEA-BISSAU AT 13N16W CONTINUING ALONG 14N30W TO 9N49W. THE ITCZ BEGINS AT 9N49W CONTINUING TO 9N61W. NO DEEP CONVECTION IS ALONG THE AXIS...BUT A LARGE BURST OF CONVECTION IS NEARING THE AFRICAN COASTLINE. ...DISCUSSION... GULF OF MEXICO... A PAIR OF UPPER LEVEL LOWS CONTINUE TO IMPACT THE GULF OF MEXICO TONIGHT SUPPORTING SHOWERS/THUNDERSTORMS IN THE NE AND SW CORNER. THE FIRST UPPER LOW IS CENTERED OVER ERN GEORGIA NEAR 32N82W SUPPORTING WIDESPREAD SHOWERS/THUNDERSTORMS N OF 27N BETWEEN 86W-92W ACROSS MUCH OF MISSISSIPPI AND ERN LOUISIANA. THE SECOND UPPER LOW IS CENTERED OVER THE ERN BAY OF CAMPECHE NEAR 20N91W. IT IS SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE YUCATAN PENINSULA. A TROPICAL WAVE IS IMMEDIATELY W OF THE UPPER LOW PLACING IT ON THE CONFLUENT SIDE OF THE UPPER LOW...WHICH IS LIMITING CONVECTION NEAR THE WAVE AS DRY AIR WRAPS AROUND IT. HOWEVER...SCATTERED SHOWERS/THUNDERSTORMS ARE ACROSS THE FAR WRN BAY OF CAMPECHE DUE TO A THIRD UPPER LEVEL LOW/TROUGH THAT IS CENTERED OVER N CENTRAL MEXICO WITH TROUGH AXIS EXTENDING DOWN THE CENTER OF THE COUNTRY PLACING THE EXTREME WRN GULF UNDER THE DIFFLUENT SIDE OF THE LOW/TROUGH. THE REMAINDER OF THE GULF IS COVERED BY AN UPPER LEVEL RIDGE ACROSS THE NRN PORTION OF THE BASIN SUPPORTING A WEAK SURFACE RIDGE AROUND A 1020 MB HIGH OVER SW ALABAMA. BESIDES NEAR THE UPPER LOWS...DRY AIR COVERS THE BASIN KEEPING THE REMAINDER OF IT UNDER CLEAR SKIES AND FAIR CONDITIONS. WEAK SURFACE RIDGING WILL FORM REMAIN ACROSS THE BASIN AS THE UPPER LEVEL LOWS WEAKEN. MOISTURE MAY REMAIN OVER SOME PORTIONS OF THE NE GULF WHERE THE HIGHEST CHANCE OF SHOWERS/THUNDERSTORMS WILL BE. CARIBBEAN SEA... THE UPPER LEVEL LOW OVER THE ERN BAY OF CAMPECHE IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS THE YUCATAN PENINSULA AND WATERS TO THE E TO 85W. CLUSTERS OF STRONG SHOWERS/THUNDERSTORMS ARE ALSO ACROSS SRN CUBA AND ADJACENT WATERS AS WELL AS JAMAICA. THESE ARE LIKELY TIED TO DAYTIME HEATING. SIMILAR ACTIVITY COVERS MUCH OF PANAMA ASSOCIATED WITH THE E PACIFIC MONSOON TROUGH THAT EXTENDS S OF THE COUNTRY TO A 1008 MB LOW OVER NRN COLOMBIA. A FEW SCATTERED SHOWERS/THUNDERSTORMS ARE ALSO OVER HISPANIOLA DUE TO A TROPICAL WAVE ACROSS THE ERN CARIBBEAN. ISOLATED SHOWERS ARE E OF 66W ASSOCIATED WITH THE WAVE.THE REMAINDER OF THE CARIBBEAN IS EXPERIENCING FAIR WEATHER DUE TO DRY AIR ALOFT WRAPPING AROUND AN UPPER LEVEL LOW S OF CUBA NEAR 20N78W. TRADEWIND FLOW OF 20 KTS IS PRESENT OVER THE CENTRAL CARIBBEAN WITH LIGHTER WINDS TO EITHER SIDE. EXPECT THE TROPICAL WAVE TO CONTINUE MOVING WWD INTO THE CENTRAL AMERICA PROVIDING MOIST CONDITIONS ACROSS THIS AREA. A LARGE AREA OF SAHARAN DUST TRAILS BEHIND THE WAVE AND WILL LIKELY HIT THE ERN CARIBBEAN WITHIN 24 HOURS. MOIST CONDITIONS WILL ALSO LIKELY REMAIN OVER CENTRAL AMERICA. ATLANTIC OCEAN... AN UPPER LEVEL LOW CENTERED OVER ERN GEORGIA IS SUPPORTING A LINE OF SHOWERS/THUNDERSTORMS FROM 32N76W TO 28N82W ACROSS THE FLORIDA PENINSULA. THE REMAINDER OF THE W ATLC IS DOMINATED BY SURFACE RIDGING AROUND A 1028 MB HIGH NEAR 34N45W PROVIDING MOSTLY FAIR CONDITIONS. THE HIGH IS SUPPORTED BY AN UPPER LEVEL RIDGE CENTERED NEAR 26N54W. AN UPPER LEVEL LOW IS TO THE W CENTERED NEAR 29N65W WITH A TROUGH AXIS EXTENDING TO AN UPPER LEVEL LOW IN THE CENTRAL CARIBBEAN. THE TROUGH AXIS IS SUPPORTING SOME ISOLATED SHOWERS ACROSS THE ERN BAHAMAS AND THE AREA N OF THE ERN CARIBBEAN. THE AFOREMENTIONED SURFACE HIGH IS ALSO PROVIDING RIDGING ACROSS THE CENTRAL AND ERN ATLC WHERE FAIR WEATHER DOMINATES. AN UPPER LEVEL TROUGH EXTENDS FROM E OF THE AZORES ISLANDS TO NEAR 28N40W...BUT IS NOT CAUSING ANY SIGNIFICANT WEATHER. UPPER LEVEL RIDGING ALSO COVERS THE FAR ERN ATLC CENTERED JUST OFF THE AFRICAN COAST NEAR 17N20W. THE LAST VISIBLE SATELLITE IMAGERY INDICATES A LARGE AREA OF SAHARAN DUST COVERS MUCH OF THE TROPICAL ATLC AROUND THE TROPICAL WAVES...WHICH IS HELPING SUPPORT FAIR SURFACE CONDITIONS. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ WALTON