000 AXNT20 KNHC 271009 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 AM 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0945 UTC. ...SPECIAL FEATURES... TROPICAL STORM KAREN HAS WEAKENED SLIGHTLY OVER THE OPEN WATERS OF THE CENTRAL ATLANTIC. AT 27/0900 UTC KAREN WAS NEAR 13.6N 46.6W OR ABOUT 840 NM EAST OF THE WINDWARD ISLANDS...MOVING W-NW AT 13 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 998 MB. MAXIMUM SUSTAINED WINDS ARE 55 KT WITH GUSTS TO 65 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...FURTHER WEAKENING IS EXPECTED. MODERATE CONVECTION IS MOSTLY DISPLACED NE OF THE CENTER FROM 13N-17N BETWEEN 41W-46W. THE CENTER OF KAREN IS JUST S OF NOAA BUOY 41041...WHICH RECENTLY REPORTED A GUST FROM THE E AT 47 KT. SEAS AT THIS BUOY HAVE STAYED IN THE 20 TO 23 FT RANGE OVER THE LAST FEW HOURS...AND COULD EVEN BE A FEW FEET HIGHER A LITTLE FURTHER S CLOSER TO THE CORE. A MODERATE TO STRONG LONGER PERIOD E SWELL WILL RACE AHEAD OF KAREN AND AFFECT EAST EXPOSED BEACHES OF THE LESSER ANTILLES LATE FRIDAY THROUGH THE WEEKEND. TROPICAL DEPRESSION THIRTEEN AT 27/0900 UTC WAS OVER THE SW GULF OF MEXICO NEAR 20.8N 95.1W OR ABOUT 180 NM EAST-SOUTHEAST OF TAMPICO MEXICO AND ABOUT 130 NM EAST OF TUXPAN MEXICO. THE DEPRESSION IS DRIFTING W-SW NEAR 3 KT. A SLOW MOTION TO THE WEST IS EXPECTED OVER THE NEXT 24 HOURS. ESTIMATED MINIMUM CENTRAL PRESSURE REPORTED BY THE HURRICANE HUNTER IS 1008 MB. MAXIMUM SUSTAINED WINDS ARE 30 KT WITH GUSTS TO 40 KT. THE DEPRESSION IS FORECAST TO BECOME A TROPICAL STORM LATER TODAY. SEE LATEST NHC FORECAST ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC AND THE PUBLIC ADVISORY UNDER MIATCPAT3/WTNT33 KNHC FOR MORE DETAILS...INCLUDING THE LATEST WATCH AND WARNING INFORMATION. INCREASING MODERATE CONVECTION IS MOSTLY WITHIN 120 NM SW SEMICIRCLE. TROPICAL DEPRESSION THIRTEEN IS FORECAST TO MAKE LANDFALL ON THE COAST OF MEXICO IN ABOUT 36 HOURS...AND 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. ...TROPICAL WAVES... A TROPICAL WAVE IS OVER THE E ATLC AND CAPE VERDE ISLANDS ALONG 24W SOUTH OF 17W MOVING W 10-15 KT. THE WAVE SHOWS UP WELL IN LOW LEVEL SATELLITE DERIVED WINDS AND VORTICITY...AND THE UW CIMSS TPW PRODUCTS. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 180 NM EITHER SIDE OF AXIS...MAINLY FROM 10N-14N. THIS WAVE HAS BECOME A LITTLE BETTER ORGANIZED THIS MORNING...AND SOME SLOW DEVELOPMENT OF THIS SYSTEM IS POSSIBLE OVER THE NEXT COUPLE OF DAYS. A TROPICAL WAVE IS OVER THE CARIBBEAN AND SW NORTH ATLC ALONG 71W S OF 23N MOVING W 10-15 KT. SCATTERED SHOWERS/ISOLATED TSTMS ARE WITHIN 300 NM EITHER SIDE OF THE WAVE AXIS N OF 14N....AFFECTING THE NORTH CENTRAL CARIBBEAN N THROUGH THE TURKS AND CAICOS. THE CLUSTER OF MODERATE TO STRONG CONVECTION AFFECTING HISPANIOLA LAST NIGHT HAS DIMINISHED. UPPER-LEVEL WINDS ARE NOT FAVORABLE FOR DEVELOPMENT OF THIS SYSTEM. THE ASSOCIATED SHOWER ACTIVITY IS EXPECTED SPREAD INTO ERN CUBA AND JAMAICA THROUGH FRIDAY. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 9N13W 11N22W 7N31W 13N41W 4N55W. BESIDES FOR THE ACTIVITY ASSOCIATED WITH T.S. KAREN AND THE TROPICAL WAVE OVER THE E ATLC...SCATTERED MODERATE CONVECTION IS NEAR THE COAST OF AFRICA WITHIN 90 NM EITHER SIDE OF THE AXIS E OF 17W...AND BETWEEN 31W-36W. DISCUSSION... GULF OF MEXICO... THE MAIN WEATHER FEATURE ACROSS THE GULF OF MEXICO IS TROPICAL DEPRESSION THIRTEEN LOCATED IN THE SW PORTION. A TROPICAL STORM WATCH REMAINS IN EFFECT FOR THE COAST OF MEXICO FROM PALMA SOLA TO LA CRUZ. SEE SPECIAL FEATURES ABOVE FOR DETAILS. THE SFC LOW S OF KEY WEST YESTERDAY HAS WEAKENED...AND A NEW LOW MAY BE FORMING OFFSHORE CENTRAL FLORIDA IN THE WRN ATLC. SEE THAT SECTION BELOW FOR DETAILS. DRIER AIR IS FILTERING INTO THE E GULF IN WAKE OF THE DEEP LAYER TROUGHING OVER THE FLORIDA PENINSULA. IN FACT...BESIDES FOR T.D. 13 OVER THE FAR SW PORTION...THE GULF IS PRETTY TRANQUIL THIS MORNING WITH A WEAK SFC PRES GRADIENT N OF 23N AND ABUNDANT NLY FLOW ALOFT BETWEEN RIDGING BUILDING INTO THE WRN PORTION AND THE TROUGHING OVER FLORIDA. CARIBBEAN SEA... A TROPICAL WAVE IS MOVING WWD ACROSS THE CENTRAL CARIBBEAN. THE WAVE...COUPLED WITH A DIFFLUENT PATTERN ALOFT IS GENERATING WIDELY SCATTERED MODERATE CONVECTION N OF 14N BETWEEN 65W-79W. SIMILAR TO YESTERDAY MORNING...SCATTERED TSTMS ARE JUST OFFSHORE THE COAST OF COLOMBIA FROM 11N-13N BETWEEN 74W-78W. ISOLATED TSTMS ARE S OF CUBA/N OF 15N BETWEEN 77W-82W...NEAR THE BASE OF THE MID TO UPPER TROUGH EXTENDING S FROM FLORIDA/WRN ATLC. TRADES REMAIN LIGHT TO MODERATE ACROSS THE BASIN...BUT WINDS/SEAS COULD BE HIGHER AT TIMES NEAR SQUALLS ASSOCIATED WITH THE TROPICAL WAVE. ELSEWHERE ALOFT...A LARGE UPPER HIGH IS S OF HISPANIOLA SUPPORTING ABUNDANT TROPICAL MOISTURE E OF 78W. ATLANTIC OCEAN... A SFC TROUGH IS OVER THE WRN ATLC EXTENDING FROM THE STRAITS OF FLORIDA TO THE SOUTH CAROLINA COAST. THIS IS GENERATING A LARGE AREA OF CLOUDINESS AND SHOWERS OVER THE WRN ATLC BETWEEN 75W-80W...WITH LIGHTNING DATA DEPICTING MOST OF THE TSTM ACTIVITY CONCENTRATED OVER AND JUST NE OF THE NW BAHAMAS. A NEW AREA OF LOW PRESSURE COULD BE DEVELOPING OFF THE FLORIDA EAST-CENTRAL COAST...AND SLOW DEVELOPMENT OF THIS SYSTEM IS POSSIBLE DURING THE NEXT COUPLE OF DAYS AS IT MOVES NORTHEASTWARD. UPPER FLOW REMAINS VERY DIFLUENT OVER THIS AREA BETWEEN TROUGHING THROUGH FLORIDA AND RIDGING EXTENDING N FROM THE CARIBBEAN ALONG 69W. THIS UPPER DIFFLUENCE IS ALSO SUPPORTING SCATTERED SHOWERS AND ISOLATED TSTMS NEAR THE NRN PORTION OF THE CENTRAL CARIBBEAN TROPICAL WAVE BETWEEN 66W-74W. THE REMAINDER OF THE CENTRAL ATLC IS DOMINATED BY A SFC TROUGH ENTERING THE AREA NEAR 32N33W AND CONTINUING SW TO 23N44W. THE TROUGH IS AHEAD OF A COLD FRONT CLIPPING THE AREA ALONG 32N39W 27N54W 29N63W. THE TROUGH AND FRONT APPEAR TO BE MERGING WITH IT BECOMING DIFFICULT TO LOCATE TWO SEPARATE BOUNDARIES. THE COMBINED EFFECT IS PRODUCING SCATTERED SHOWER ACTIVITY FROM 20N-27N BETWEEN 42W-60W. 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 THE LAST FEW DAYS IS NOW E OF THE MADEIRA ISLANDS NEAR 32N15W. SHOWER ACTIVITY HAS MOSTLY DIMINISHED WITH THIS UPPER LOW...WHICH IS EXPECTED TO MOVE NE OF THE AREA WHILE OPENING INTO A TROUGH THROUGH FRI. $$ WILLIS