000 AXNT20 KNHC 272349 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT THU SEP 27 2007 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN SECTIONS OF SOUTH AMERICA...AND THE 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... TROPICAL STORM KAREN HAS WEAKENED SLIGHTLY BUT STILL A TROPICAL STORM OVER THE OPEN WATERS OF THE CENTRAL ATLANTIC. AT 27/2100 UTC KAREN WAS NEAR 14.3N 48.5W OR ABOUT 735 NM EAST OF THE WINDWARD ISLANDS...MOVING WEST NORTHWEST NEAR 11 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1005 MB. MAXIMUM SUSTAINED WINDS ARE 50 KT WITH GUSTS TO 60 KT. SEE LATEST NHC FORECAST ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC AND THE PUBLIC ADVISORY UNDER MIATCPAT2/WTNT32 KNHC FOR MORE DETAILS. MODERATE TO STRONG SOUTHWESTERLY SHEAR AHEAD OF A MID-OCEANIC TROUGH IS AFFECTING KAREN AND THIS SHEAR IS EXPECTED TO PERSIST OVER THE NEXT FEW DAYS. THUS...A GRADUAL WEAKENING IS FORECAST. LATEST SATELLITE IMAGERY SHOWS THAT KAREN'S CENTER IS CLOSE TO THE DEEP CONVECTION. MODERATE TO STRONG CONVECTION IS FROM 14N-17N BETWEEN 46W-50W. A BAND OF SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS WITHIN 300 NM EAST OF CENTER FROM 11N-17N. TROPICAL DEPRESSION THIRTEEN WAS UPGRADED TO TROPICAL STORM LORENZO AT 1800 UTC...THE TWELFTH NAMED STORM OF THE 2007 HURRICANE SEASON. REPORTS FROM AN AIR FORCE PLANE INVESTIGATING LORENZO INDICATE THAT THE WINDS HAVE BEEN INCREASING AND THE PRESSURE HAS COME DOWN TO AT LEAST 999 MB. SOME ADDITIONAL STRENGTHENING IS FORECAST AND LORENZO COULD REACH THE MEXICAN COAST AS A HURRICANE BECAUSE THE SHEAR IS LOW AND THE OCEAN IS WARM. AT 27/2100 UTC IT WAS NEAR 20.4N 95.9W OR ABOUT 90 NM...170 KM...EAST-SOUTHEAST OF TUXPAN MEXICO...MOVING WEST NEAR 4 KT...AND THIS GENERAL MOTION TOWARD THE COAST OF MEXICO IS EXPECTED UNTIL THE CENTER CROSSES THIS COAST IN ABOUT 12 HOURS OR SO. SEE LATEST NHC FORECAST ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC AND THE PUBLIC ADVISORY UNDER MIATCPAT3/ WTNT33 KNHC FOR MORE DETAILS. WATCHES AND WARNINGS HAVE BEEN ISSUED. LORENZO IS EXPECTED TO PRODUCE TOTAL RAINFALL ACCUMULATIONS OF 5 TO 10 INCHES OVER THE MEXICAN STATE OF VERACRUZ...WITH POSSIBLE ISOLATED MAXIMUM AMOUNTS OF 15 INCHES. VERACRUZ WAS REPORTING STEADY LIGHT RAIN DURING THE LAST SEVERAL HOURS AND POZA RICA HEAVY RAIN AT TIMES. NUMEROUS MODERATE TO SCATTERED STRONG CONVECTION IS WITHIN 100 NM OF 20N95W. ...TROPICAL WAVES... A TROPICAL WAVE IS OVER THE E ATLC ALONG 26W SOUTH OF 19W MOVING W 10-15 KT. THE WAVE SHOWS UP WELL IN LOW LEVEL SATELLITE DERIVED WINDS AND VORTICITY...AND THE UW CIMSS TPW PRODUCTS WITH A GOOD MOISTURE SURGE. SHOWERS AND THUNDERSTORMS ASSOCIATED WITH THE WAVE HAVE DECREASED...AND SIGNIFICANT DEVELOPMENT OF THIS SYSTEM IS NOT ANTICIPATED. WIDELY SCATTERED MODERATE CONVECTION IS WITHIN 90 NM EITHER SIDE OF AXIS...MAINLY FROM 10N-14N. A TROPICAL WAVE IS OVER THE CARIBBEAN ALONG 74W S OF 21N MOVING W NEAR 15 KT. THIS WAVE IS PRODUCING DISORGANIZED CLOUDINESS AND SHOWERS FROM THE CENTRAL CARIBBEAN SEA NORTHWARD ACROSS HISPANIOLA...THE SOUTHEASTERN BAHAMAS...AND THE ADJACENT ATLANTIC. DEVELOPMENT IS NOT EXPECTED. A CLUSTER OF MODERATE TO ISOLATED STRONG CONVECTION HAS DEVELOPED OVER HISPANIOLA...JUST BEHIND THE WAVE AXIS. SIMILAR CONVECTION IS SEEN ON THE SOUTH END OF THE WAVE OVER WESTERN VENEZUELA AND NORTHERN COLOMBIA. THIS CONVECTIVE ACTIVITY IS BEEN ENHANCING BY UPPER DIFFLUENT. MOISTURE ASSOCIATED WITH THIS WAVE IS FORECAST TO SPREAD OVER EASTERN CUBA AND JAMAICA TOMORROW. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 7N12W 10N24W 8N35W 12N42W 8N60W. BESIDES FOR THE ACTIVITY ASSOCIATED WITH T.S. KAREN AND THE TROPICAL WAVE OVER THE E ATLC...SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS NEAR THE COAST OF AFRICA FROM 11N-14N BETWEEN 12W-16W. DISCUSSION... GULF OF MEXICO... TROPICAL STORM LORENZO...WHICH IS FORECAST TO IMPACT MEXICO THIS FRIDAY IS THE MAIN WEATHER FEATURE ACROSS THE GULF OF MEXICO. THE SLOW MOTION OF LORENZO WILL LIKELY PRODUCE TORRENTIAL RAINFALL ALONG ITS PATH. SEE SPECIAL FEATURES ABOVE FOR MORE DETAILS. AN UPPER RIDGE ANCHORED ON A HIGH OVER NE MEXICO DOMINATES MUCH OF THE REGION...INCLUDING THE YUCATAN PENINSULA. DRIER AIR IS FILTERING INTO THE E GULF IN WAKE OF THE DEEP LAYER TROUGHING OVER THE FLORIDA PENINSULA. IN FACT... BESIDES FOR LORENZO IN THE FAR SW PORTION...THE GULF IS PRETTY TRANQUIL WITH A WEAK SFC PRES GRADIENT N OF 23N. UPPER DIFFLUENCE BETWEEN THE AFOREMENTIONED RIDGE AND A DEEP LAYERED UPPER-LEVEL TROUGH MOVING E OVER THE EASTERN U.S. IS HELPING TO INDUCE SCATTERED SHOWERS AND ISOLATED TSTMS OVER THE NORTHERN GULF WATERS JUST SOUTH OF THE LOUISIANA COAST. CARIBBEAN SEA... A TROPICAL WAVE IS MOVING WWD ACROSS THE CENTRAL CARIBBEAN. SEE TROPICAL WAVE SECTION. SCATTERED SHOWERS AND TSTMS ARE OVER PANAMA AND COSTA RICA DUE TO THE ITCZ. AN UPPER-LEVEL LOW HAS DEVELOPED OVER WESTERN CUBA ALONG THE UPPER-LEVEL TROUGH THAT CROSSES THE FLORIDA PENINSULA AND THE NW CARIBBEAN. UPPER DIFFLUENCE BETWEEN THIS LOW/TROUGH AND AN UPPER RIDGE OVER THE CENTRAL CARIBBEAN...JUST SOUTH OF HISPANIOLA IS SUPPORTING THE SHOWERS AND TSTMS OVER EAST-CENTRAL CUBA. SIMILAR ACTIVITY IS OVER NORTHERN CENTRAL AMERICA NEAR THE BASE OF THE TROUGH. TRADE WINDS REMAIN LIGHT TO MODERATE ACROSS THE BASIN...BUT WINDS/SEAS COULD BE HIGHER AT TIMES NEAR SQUALLS ASSOCIATED WITH THE TROPICAL WAVE. NWLY UPPER WINDS ASSOCIATED WITH AN UPPER LOW LOCATED OVER THE CENTRAL ATLC ARE ADVECTING HIGH CLOUDS/MID TO UPPER LEVEL MOISTURE OVER PUERTO RICO AND THE NE CARIBBEAN INTO THE LESSER ANTILLES. ATLANTIC OCEAN... A TROUGH OF LOW PRESSURE EXTENDING FROM JUST OFFSHORE THE EAST COAST OF FLORIDA NORTH-NORTHEASTWARD ACROSS THE ATLANTIC FOR SEVERAL HUNDRED MILES IS PRODUCING DISORGANIZED CLOUDINESS AND THUNDERSTORMS OVER THE WESTERN ATLC AND THE BAHAMAS WEST OF 70W. LIGHTNING DATA DEPICTS MOST OF THE TSTM ACTIVITY WITHIN 300 NM EAST OF THE TROUGH AXIS. A 1010 MB SFC LOW IS ANALYZED ALONG THE TROUGH AXIS NEAR 29N78W. THIS SYSTEM HAS BECOME LESS ORGANIZED DURING THE DAY AND SIGNIFICANT DEVELOPMENT OF THIS DISTURBANCE IS NOT EXPECTED BEFORE IT BECOMES ABSORBED BY A FRONTAL SYSTEM IN THE NEXT COUPLE OF DAYS. UPPER FLOW REMAINS VERY DIFLUENT OVER THIS AREA BETWEEN TROUGHING THROUGH FLORIDA AND RIDGING EXTENDING N FROM THE CARIBBEAN ALONG 70W. AN UPPER LOW OVER THE CENTRAL ATLC NEAR 22N56W IS GENERATING SOME SHOWER ACTIVITY. A SFC TROUGH WAS ANALYZED OVER THIS AREA DURING THE PREVIOUS DAYS. MODERATE SFC RIDGING REMAINS ANCHORED OVER THE E ATLC... PRODUCING LIGHT TO MODERATE NE TRADES E OF 30W. THE UPPER LOW THAT HAS BEEN AFFECTING THE FAR NE PORTION OF THE DISCUSSION AREA IS MOVING NE APPROACHING PORTUGAL. AN UPPER RIDGE DOMINATES THE TROPICAL ATLC WITH AN UPPER HIGH NEAR 12N35W. $$ GR