000 AXNT20 KNHC 300003 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT MON SEP 29 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... SUBTROPICAL STORM LAURA IS CENTERED NEAR 38.3N 48.4W AT 29/2100 UTC OR ABOUT 545 NM SSE OF CAPE RACE NEWFOUNDLAND MOVING NNW AT 8 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 995 MB. MAXIMUM SUSTAINED WIND SPEED IS 50 KT WITH GUSTS TO 60 KT. LAURA IS EXPECTED TO TURN TOWARD THE N THEN NNE WITH AN INCREASE IN FORWARD SPEED DURING THE NEXT COUPLE OF DAYS. TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 210 NM FROM THE CENTER. SCATTERED MODERATE CONVECTION IS FOUND WITHIN 150 NM OF THE CENTER IN THE ERN SEMICIRCLE OF LAURA. LAURA IS EXPECTED TO STRENGTHEN SOME DURING THE NEXT 24 HOURS BEFORE MOVING OVER COLDER WATERS...AND IS EXPECTED TO TRANSITION TO A TROPICAL STORM TONIGHT. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT2/ WTNT32 KNHC FOR MORE DETAILS. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 28W S OF 15N MOVING W 10-15 KT. SATELLITE IMAGERY DEPICTS WELL-DEFINED INVERTED-V STRUCTURE TO LOW/MID-LEVEL CLOUD PATTERN ALONG WAVE AXIS...WHERE COMPUTER MODEL GUIDANCE CONFIRMS WEAK LOW LEVEL CIRCULATION. MIMIC TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS ALSO SHOWS WAVE IS EMBEDDED WITHIN DEEP LAYER MOISTURE MAXIMUM. ISOLATED MODERATE CONVECTION IS WITHIN 90 NM OF WAVE AXIS S OF 6N...AND ADDITIONAL ISOLATED MODERATE CONVECTION IS WITHIN 120 NM OF WAVE AXIS N OF 12N. A TROPICAL WAVE IS ALONG 42W/43W FROM 10N-20N MOVING W 5-10 KT. SATELLITE IMAGERY CONTINUES TO DEPICT BROAD-LOW LEVEL CIRCULATION CENTERED ALONG WAVE AXIS NEAR 15N. DEEP LAYER MOISTURE IS ALSO BROADLY DISTRIBUTED AROUND WAVE. THIS WAVE IS DIRECTLY BENEATH AN UPPER HIGH...RESULTING IN STABLE ATMOSPHERIC CONDITIONS PREVENTING ANY DEEP CONVECTION NEAR THE WAVE. A TROPICAL WAVE IS ALONG 56W/57W S OF 16N MOVING W NEAR 10 KT. OTHER THAN A WEAK ENHANCEMENT IN TOTAL PRECIPITABLE WATER NEAR THE WAVE...THIS WAVE IS ILL-DEFINED. STABLE CONDITIONS BENEATH AN UPPER RIDGE ARE PREVENTING DEEP CONVECTIVE DEVELOPMENT NEAR THE WAVE. ...THE ITCZ... THE ITCZ AXIS IS ANALYZED ALONG 12N15W 11N25W 7N33W 7N46W 10N60W. IN ADDITION TO CONVECTION ASSOCIATED WITH THE TROPICAL WAVES...CLUSTERS OF MODERATE/ISOLATED STRONG CONVECTION ARE MOVING WESTWARD TOWARD THE W COAST OF AFRICA...AFFECTING S SENEGAL...GAMBIA...AND GUINEA-BISSAU. ISOLATED MODERATE CONVECTION IS FROM 3N-8N BETWEEN 36W-41W. ISOLATED MODERATE CONVECTION IS FROM 9N-12N BETWEEN 60W-70W AFFECTING N VENEZUELA. ...DISCUSSION... GULF OF MEXICO... AN UPPER TROUGH IS OVER THE W GULF...WITH THE TROUGH AXIS EXTENDING FROM SW LOUISIANA TO THE BAY OF CAMPECHE. MOIST SOUTHWESTERLY FLOW ALOFT IS E OF THE TROUGH AXIS...PROVIDING UPPER LEVEL SUPPORT FOR NUMEROUS SHOWERS AND THUNDERSTORMS OVER THE E GULF. ADDITIONALLY...A 1012 MB SURFACE LOW IS OVER THE S/CENTRAL GULF NEAR 23N88W. A SURFACE TROUGH EXTENDS FROM THE COAST OF FLORIDA NEAR 26N82W WESTWARD TO THE LOW AND THEN TO THE SW OVER THE YUCATAN PENINSULA. LOW LEVEL CONVERGENCE NEAR THESE FEATURES IS FURTHER ENHANCING THE SHOWERS AND THUNDERSTORMS OVER THE E GULF S OF 28N...AFFECTING MUCH OF S FLORIDA AND W CUBA. TO THE W OF THE UPPER TROUGH AXIS...DEEP LAYER DRY AIR AND SUBSIDENCE ARE RESULTING IN FAIR WEATHER OVER THE W GULF...WHERE A WEAK SURFACE RIDGE IS BUILDING FROM THE NW. CARIBBEAN SEA... AN UPPER LOW IS OVER N VENEZUELA...WITH AN UPPER HIGH LOCATED OVER THE SW ATLANTIC. E FLOW ALOFT BETWEEN THESE FEATURES IS SPREADING DEEP LAYER DRY AIR ACROSS MUCH OF THE CENTRAL AND E CARIBBEAN RESULTING IN MOSTLY FAIR WEATHER...WITH ONLY ISOLATED SHOWERS E OF 70W AND S OF 15N. A WEAK UPPER TROUGH EXTENDS FROM CENTRAL AMERICA NORTHWARD INTO THE SW CARIBBEAN. THIS TROUGH IS GENERATING DIFFLUENT UPPER FLOW IN THE W CARIBBEAN...WHERE SCATTERED MODERATE CONVECTION IS OCCURRING W OF 80W INCLUDING HONDURAS AND NICARAGUA...AS WELL AS OVER PANAMA. CLUSTERS OF MODERATE CONVECTION OVER FAR NW VENEZUELA ARE MOVING INTO THE ADJACENT COASTAL WATERS OF THE S CARIBBEAN. TRADE WINDS OF 10 TO 20 KT PERSIST THROUGHOUT THE CARIBBEAN. ATLANTIC OCEAN... SUBTROPICAL STORM LAURA IS LOCATED IN THE N/CENTRAL ATLANTIC... SEE SPECIAL FEATURES SECTION ABOVE. THE W ATLC IS BETWEEN AN UPPER TROUGH OVER THE W GULF...AND AN UPPER HIGH E OF THE BAHAMAS CENTERED NEAR 24N69W. AS A RESULT...MOIST SW FLOW ALOFT CONTINUES OVER THE W ATLC W OF 74W....WITH SCATTERED SHOWERS AND THUNDERSTORMS OVER THE SW ATLANTIC...AFFECTING S FLORIDA...THE BAHAMAS...AND CUBA. THIS ACTIVITY IS BEING ENHANCED BY A SURFACE TROUGH EXTENDING FROM S FLORIDA NEAR 27N80W EASTWARD TO NEAR 29N77W. BENEATH THE UPPER HIGH IS A 1016 MB SURFACE HIGH CENTERED NEAR 26N67W. DRY AIR AND SUBSIDENCE ASSOCIATED WITH THESE FEATURES COVER A LARGE AREA OF THE CENTRAL ATLC WHERE MOSTLY FAIR WEATHER PREDOMINATES. TO THE E...AN UPPER TROUGH COVERS PORTIONS OF THE CENTRAL ATLANTIC E OF SUBTROPICAL STORM LAURA...AND EXTENDS FROM 32N41W SOUTHWARD TO 23N50W TO NEAR THE LESSER ANTILLES NEAR 14N61W. STRONG FLOW ALOFT E OF THE TROUGH AXIS IS SUPPORTING SCATTERED MODERATE CONVECTION FROM 26N-32N BETWEEN 36W-42W. S OF 23N...THIS UPPER TROUGH IS SHARPENED BETWEEN THE UPPER HIGH E OF THE BAHAMAS...AND AN UPPER RIDGE FURTHER TO THE E. THIS RIDGE COVERS MUCH OF THE E ATLC...AND EXTENDS TO THE W OF AN UPPER HIGH NEAR 19N23W TO NEAR 17N46W. S OF THIS RIDGE...DEEP LAYER E FLOW IS PRESENT...WITH A SURFACE RIDGE OVER THE E ATLANTIC ALONG 31W N OF 21N. $$ COHEN