000 AXNT20 KNHC 202350 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT MON AUG 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... THE CENTER OF POST-TROPICAL CYCLONE GORDON AT 20/2100 UTC IS NEAR 39.2N 20.3W...OR ABOUT 320 NM ENE OF THE AZORES ISLANDS. GORDON IS MOVING ENE AT 14 KNOTS. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1000 MB. THE MAXIMUM SUSTAINED WIND SPEED IS 40 KT WITH GUSTS TO 50 KT. PLEASE READ THE NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC AND THE PUBLIC ADVISORY UNDER MIATCPAT3/WTNT33 KNHC FOR MORE DETAILS. SCATTERED MODERATE CONVECTION IS FROM 40N-42N BETWEEN 18W-21W. TROPICAL WAVE EXTENDS FROM NEAR 22N45W TO A WELL-DEFINED 1009 MB SURFACE LOW AT 16N47W. THE SYSTEM IS MOVING WEST AT 20 KT. IT CONTINUES TO ALIGN WELL WITH A LARGE SURGE OF DEEP LAYER MOISTURE WITH MAXIMUM VALUES NEAR THE LOW CENTER. THERE CONTINUES TO BE DRY AIR AND DUST WRAPPING AROUND THE NORTHERN EXTENT OF THE WAVE...WHICH MAY EXPLAIN THE LACK OF DEEP CONVECTION NEAR THE CENTER. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS MAINLY S OF THE LOW CENTER FROM 11N-14N BETWEEN 43W-49W...AND FROM 14N-16N BETWEEN 48W-51W. IF CONVECTION INCREASES NEAR THE LOW CENTER...THEN A TROPICAL DEPRESSION COULD FORM. TROPICAL WAVE EXTENDS FROM THE CAPE VERDE ISLANDS NEAR 18N23W TO A 1010 MB SURFACE LOW NEAR 12N27W. THE LOW IS EMBEDDED WITHIN THE MONSOON TROUGH...AN AN ASCAT PASS FROM EARLIER TODAY INDICATES THAT THE LOW CENTER MAY ACTUALLY BE FARTHER SOUTH NEAR 10N. THE SYSTEM LIES ON THE WEST SIDE OF A SURGE OF DEEP LAYER MOISTURE PRESENT IN TOTAL PRECIPITABLE WATER IMAGERY. IT ALSO LIES WITHIN A CLEARING OF THE SAHARAN AIR LAYER THAT SURROUNDING THE WAVE. A CLUSTER OF SCATTERED STRONG CONVECTION IS SW OF THE LOW CENTER FROM 7N-11N BETWEEN 27W-31W. SOME GRADUAL DEVELOPMENT OF THE SYSTEM IS POSSIBLE OVER THE NEXT COUPLE OF DAYS AS IT MOVES W AT 15-20 KT. A SURFACE TROUGH IN THE GULF OF MEXICO IS PRODUCING A LARGE AREA OF SHOWERS/THUNDERSTORMS ACROSS THE BASIN. THE PORTION BEING MONITORED FOR POSSIBLE DEVELOPMENT IS IN THE WESTERN GULF NEAR THE COAST OF MEXICO. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATED THE SYSTEM A FEW HOURS AGO AND FOUND AN ELONGATED AREA OF LOW PRESSURE...BUT NOT A CLEAR LOW CENTER. CONVECTION NEAR THIS PORTION OF THE TROUGH HAS ACTUALLY DIMINISHED OVER THE PAST FEW HOURS. SCATTERED MODERATE CONVECTION STILL REMAINS FROM 21N-24N BETWEEN 95W-98W...WITH VERY DISORGANIZED SCATTERED MODERATE/ISOLATED STRONG CONVECTION EXTENDING INLAND OVER MEXICO TO 103W. IF THE SYSTEM REMAINS OVER WATER...SOME GRADUAL DEVELOPMENT IS POSSIBLE OVER THE NEXT COUPLE OF DAYS. ...TROPICAL WAVES... TWO TROPICAL WAVES IN THE CENTRAL AND EASTERN TROPICAL ATLC ARE DESCRIBED IN THE SPECIAL FEATURES SECTION ABOVE. TROPICAL WAVE IS ALONG 18N56W TO 10N56W MOVING W AT 15-20 KT. THE WAVE ALIGNS WELL WITH A NARROW SURGE OF DEEP LAYER MOISTURE PRESENT IN TOTAL PRECIPITABLE WATER IMAGERY. ONLY A SMALL AREA OF ISOLATED MODERATE CONVECTION IS W OF THE AXIS FROM 16N-18N BETWEEN 56W-59W. WEAK TROPICAL WAVE IS MOVING THROUGH CENTRAL AMERICA AND THE WESTERN CARIBBEAN FROM 20N85W TO 11N85W. THE WAVE IS MOVING WEST AT 15-20 KT. IT LIES ON THE WEST SIDE OF A LARGE AREA OF ENHANCED MOISTURE VALUES COVERING THE WESTERN HALF OF THE CARIBBEAN. THE WAVE LIES BETWEEN AN UPPER LEVEL LOW TO THE WEST AND AN UPPER LEVEL RIDGE TO THE EAST...WHICH MEANS THAT MOIST SLY FLOW ALOFT IS OVER THE WAVE. CONVECTION IS CONCENTRATED ALONG THE WAVE AXIS MAINLY OVER CENTRAL AMERICA INCLUDING HONDURAS...NICARAGUA...AND COSTA RICA. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS ALSO OFFSHORE FROM 11N-14N BETWEEN 79W-84W WITH SIMILAR ACTIVITY ACROSS COSTA RICA AND PANAMA. THIS ACTIVITY MAY BE MORE ASSOCIATED WITH DIFFLUENCE ALOFT AND THE PRESENCE OF THE MONSOON TROUGH WHICH EXTENDS THROUGH PANAMA TO NORTHERN COLOMBIA. ...THE ITCZ/THE MONSOON TROUGH... THE MONSOON TROUGH EXTENDS ACROSS WEST AFRICA TO THE COAST OF SENEGAL AT 13N17W TO A 1010 MB SURFACE LOW AT 12N28W WHERE IT MAKES A U-SHAPE ALONG 8N31W TO 10N38W. THERE IS A BREAK IN THE MONSOON TROUGH DUE TO THE LARGE CIRCULATION AROUND A 1009 MB SURFACE LOW AT 16N47W. IT BEGINS AGAIN AT THIS LOW CENTER CONTINUING ALONG 11N50W 10N54W TO 7N59W. ...DISCUSSION... THE GULF OF MEXICO... ACTIVE WEATHER IS ACROSS A LARGE PORTION OF THE GULF OF MEXICO ASSOCIATED WITH A SURFACE TROUGH EXTENDING FROM THE FLORIDA PANHANDLE AT 31N86W TO THE COAST OF MEXICO ALONG 27N91W TO 22N97W. A SWATH OF SHOWERS/THUNDERSTORMS EXTENDS 200 NM SE OF THE AXIS. THE TROUGH IS SUPPORTED BY AN UPPER LEVEL TROUGH EXTENDING FROM THE GREAT LAKES REGION TO THE EASTERN COAST OF TEXAS. THE WESTERN EXTENT OF THE SURFACE TROUGH IS BEING MONITORED FOR POSSIBLE DEVELOPMENT INTO A TROPICAL CYCLONE. SEE SPECIAL FEATURES ABOVE FOR MORE DETAILS. ELSEWHERE ACROSS THE BASIN...SURFACE RIDGING IS ACROSS THE SE GULF WITH 15-20 KT SOUTHERLY FLOW PRESENT UNTIL HITTING THE WEAK NW FLOW ON THE OPPOSITE SIDE OF THE SURFACE TROUGH. THIS CONVERGENCE IS HELPING FORM THE LINE OF THUNDERSTORMS AHEAD OF THE TROUGH AXIS. BESIDES NEAR THE SURFACE TROUGH...DRY AIR ALOFT IS OVER BOTH THE EXTREME NW GULF AND THE SE GULF...WHICH IS PROVIDING MOSTLY FAIR CONDITIONS. THE SURFACE TROUGH IS EXPECTED TO BREAK IN THE MIDDLE WITH THE NE PORTION REMAINING MOSTLY STATIONARY AND BRINGING SHOWERS/THUNDERSTORMS OVER THE NE GULF. THE WESTERN PORTION IS EXPECTED TO TAKE ON A MORE VERTICAL ORIENTATION...WITH POSSIBLE DEVELOPMENT AS MENTIONED ABOVE. THE CARIBBEAN SEA... A TROPICAL WAVE IS MOVING THROUGH THE WESTERN CARIBBEAN AND CENTRAL AMERICA CAUSING SHOWERS/THUNDERSTORMS MAINLY OVER CENTRAL AMERICA. SCATTERED SHOWER/THUNDERSTORMS ARE ALSO ACROSS THE SW CARIBBEAN INCLUDING COSTA RICA AND PANAMA ASSOCIATED WITH THE MONSOON TROUGH THAT EXTENDS THROUGH PANAMA TO A 1010 MB SURFACE LOW OVER NORTHERN COLOMBIA. SHOWER ACTIVITY NEAR BOTH THESE FEATURES IS ENHANCED BY DIFFLUENCE ALOFT BETWEEN AN UPPER LEVEL LOW OVER BELIZE...AND AN UPPER LEVEL RIDGE CENTERED NEAR 14N79W. DRY AIR ALOFT COVERS THE REMAINDER OF THE CARIBBEAN PROVIDING MOSTLY FAIR WEATHER. SEVERAL STATIONS ARE REPORTING THE PRESENCE OF DUST...WHICH IS FURTHER SUPPORTING FAIR CONDITIONS. A TROPICAL WAVE EAST OF THE LESSER ANTILLES WILL LIKELY REACH THE EASTERN CARIBBEAN WITHIN THE NEXT 12 HOURS. INTERESTS IN THE LESSER ANTILLES SHOULD ALSO MONITOR THE SYSTEM TO THE EAST OF THIS WAVE THAT IS DESCRIBED IN THE SPECIAL FEATURES SECTION. SHOWERS/THUNDERSTORMS WILL ALSO LIKELY REMAIN ACROSS CENTRAL AMERICA AND THE SW CARIBBEAN. THE ATLANTIC OCEAN... SURFACE RIDGING DOMINATES THE WEST ATLC AROUND A 1021 MB HIGH NEAR 28N61W PROVIDING MOSTLY FAIR CONDITIONS. HOWEVER...A STRONG UPPER TROUGH OVER THE EASTERN CONUS IS PRODUCING STRONG SHOWERS/THUNDERSTORMS ALONG THE EASTERN COAST OF FLORIDA AND THE OFFSHORE WATERS N OF 26N BETWEEN 78W-81W. THE RIDGE IS SUPPORTED BY A BROAD UPPER LEVEL RIDGE CENTERED TO THE N NEAR 35N60W. AN UPPER LEVEL TROUGH IS TO THE SOUTH FROM NEAR 26N59W TO 20N75W...BUT IS INFILTRATED WITH DRY AIR WHICH IS LIMITING ITS INFLUENCE TO PRODUCE ANY ACTIVE WEATHER. ONLY A SMALL AREA OF SHOWERS IS FROM 26N-28N BETWEEN 59W-64W. THE REMAINDER OF THE BASIN IS DOMINATED BY BROAD SURFACE RIDGING AROUND A 1019 MB HIGH NEAR 26N35W. THE RIDGE IS SUPPORTED BY AN UPPER LEVEL RIDGE CENTERED NEAR 21N50W. AN UPPER LEVEL TROUGH COVERS THE NE ATLC SUPPORTING A WEAK SURFACE TROUGH ENTERING THE DISCUSSION AREA ALONG 32N34W TO 29N41W. ISOLATED SHOWERS ARE WITHIN 90 NM EITHER SIDE OF THE AXIS. VISIBLE SATELLITE IMAGERY AND SATELLITE ENHANCED IMAGERY INDICATES A LARGE AREA OF SAHARAN DUST EXTENDS FROM THE COAST OF AFRICA AROUND THE SERIES OF ATLC TROPICAL WAVES TO THE EASTERN CARIBBEAN. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ WALTON