000 AXNT20 KNHC 281801 TWDAT TROPICAL WEATHER DISCUSSION... NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT THU AUG 28 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...SPECIAL FEATURES... TROPICAL STORM GUSTAV IS CENTERED NEAR 17.9N 76.2W AT 28/1800 UTC OR ABOUT 35 NM EAST OF KINGSTON JAMAICA AND ABOUT 290 NM EAST-SOUTHEAST OF GRAND CAYMAN MOVING WEST AT 4 KT. MINIMUM CENTRAL PRESSURE IS 983 MB. MAXIMUM SUSTAINED WIND SPEED IS 60 KT WITH GUSTS TO 75 KT. PLEASE SEE THE LATEST NHC FORECAST/ ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC AND/OR THE PUBLIC ADVISORY MIATCPAT2/WTNT32 KNHC FOR MORE DETAILS. GUSTAV IS VERY CLOSE TO JAMAICA. IT IS NOT CLEAR IF THE CENTER WILL PASS DIRECTLY OVER JAMAICA OR WILL HUG THE SOUTH OR NORTH COAST...BUT WITH A WEAK MID-LEVEL RIDGE OVER FLORIDA...ALL MODELS FORECAST GUSTAV TO CONTINUE GENERALLY WESTWARD FOR THE NEXT DAY OR SO. GUSTAV COULD BECOME A HURRICANE BEFORE MOVING OVER JAMAICA THIS AFTERNOON AND TONIGHT. MODERATE TO STRONG CONVECTION IS FROM 15N-19.5N BETWEEN 74W-77.5W INCLUDING THE EAST PORTION OF JAMAICA. GUSTAV IS EXPECTED TO PRODUCE TOTAL RAINFALL ACCUMULATIONS OF 6 TO 12 INCHES ACROSS JAMAICA AND THE CAYMAN ISLANDS...WITH ISOLATED MAXIMUM AMOUNTS OF UP TO 25 INCHES POSSIBLE. THESE RAINS WILL LIKELY PRODUCE LIFE-THREATENING FLASH FLOODS AND MUD SLIDES. RAINFALL ACCUMULATIONS OF 2 TO 4 INCHES ARE POSSIBLE OVER SOUTHERN CUBA. RAINFALL WILL BE DIMINISHING OVER HAITI TODAY...WITH AN ADDITIONAL 1 TO 2 INCHES OF RAINFALL POSSIBLE. AT 28/1500 UTC...T.D. EIGHT IS UPGRADED TO TROPICAL STORM HANNA. AT THIS TIME...ITS CENTER IS EXPOSED TO THE W OF THE CONCENTRATED CONVECTION NEAR 20.5N 57.2W OR ABOUT 265 NM NORTHEAST OF THE NORTHERN LEEWARD ISLANDS MOVING WEST-NORTHWEST AT 11KT. A TURN TOWARD THE NORTHWEST IS EXPECTED LATER TODAY. ON THE FORECAST TRACK...HANNA WILL MOVE AWAY FROM THE NORTHERN LEEWARD ISLANDS AND BE CENTERED WELL TO THE NORTHEAST OF THE BAHAMAS DURING THE NEXT COUPLE OF DAYS. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1002 MB. MAXIMUM SUSTAINED WIND SPEED IS 30 KT WITH GUSTS TO 40 KT. PLEASE SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC AND/OR THE PUBLIC ADVISORY MIATCPAT3/WTNT33 KNHC FOR MORE DETAILS. HANNA IS INTERACTING WITH AN UPPER-LEVEL LOW TO THE WEST THAT IS LIMITING ITS INTENSIFICATION. THE FORECAST CALLS FOR HANNA TO BECOME A HURRICANE IN ABOUT 72 HOURS OR SO. ...TROPICAL WAVES... A WELL-DEFINED TROPICAL WAVE IS LOCATED NEAR THE WEST COAST OF AFRICA AND IS ABOUT TO EMERGE OVER THE EXTREME TROPICAL EASTERN ATLANTIC. GRADUAL DEVELOPMENT OF THIS SYSTEM IS POSSIBLE DURING THE NEXT COUPLE OF DAYS AS IT MOVES WESTWARD AT ABOUT 15 MPH. AN ASCAT PASS FROM AROUND 1115 UTC SHOWED A BROAD CYCLONIC CIRCULATION FROM 10N-15N EAST OF 20W TO THE AFRICAN COAST. A TROPICAL WAVE IS ALONG 38W FROM 05N TO 21N WITH A 1009 MB LOW ALONG THE WAVE AXIS AT 17N. THE PARENT WAVE HAS MOVED W AT 15 KT OVER THE PAST 24 HOURS. SCATTERED MODERATE AND ISOLATED STRONG CONVECTION IS FLARING WITHIN 150 NM OF THE N SEMICIRCLE OF THE ASSOCIATED LOW PRES. SOME SLOW DEVELOPMENT OF THIS SYSTEM IS POSSIBLE DURING THE NEXT COUPLE OF DAYS A TROPICAL WAVE IS S OF 13N ALONG 52.5W AND HAS MOVED W ABOUT 15 KT OVER THE PAST 24 HOURS. ONLY A FEW SHOWERS ARE ENHANCED ALONG 09N E OF THE WAVE AXIS...BUT BROAD CYCLONIC TURNING IS NOTED. ...THE ITCZ... THE ITCZ AXIS IS ANALYZED ALONG 10N14W TO 10N19W THEN BECOMES ILL-DEFINED AS THE TROPICAL WAVE STRETCHES THE ITCZ NORTHWARD TO NEAR 15N AT 47W. THE AXIS THEN RETURNS SW ALONG 10N43W TO THROUGH THE WAVE AT 08N52.5W...THEN CONTINUES W AND INLAND S AMERICA AT 07N. CONVECTION IS ENHANCED...SCATTERED MODERATE AND ISOLATED STRONG...WITHIN 120 NM S AND SW OF THE ITCZ AXIS TO THE E OF 32W. ONLY ISOLATED MODERATE CONVECTION ALONG THE THE AXIS BETWEEN 40W AND 55W. ...DISCUSSION... GULF OF MEXICO... AN UPPER TROUGH DISSECTS THE GULF OF MEXICO FROM NW FLORIDA TO THE BAY OF CAMPECHE WHILE AN UPPER ANTICYCLONE IS CENTERED OVER THE CAYMAN ISLANDS. DRY UPPER AIR IS NOTED N OF 23N TO THE W OF THE UPPER TROUGH...AND IS SUPPRESSING CONVECTION TO ONLY A FEW SHOWERS OVER THE N CENTRAL GULF. A SURFACE RIDGE EXTENDS W ACROSS THE NORTHERN WATERS. THE NORTHERN EXTENSION OF A TROPICAL WAVE OVER THE E PACIFIC SPAWNED A LOW PRES OVER THE BAY OF CAMPECHE NEAR 20N94W ESTIMATED AT 1007 MB. INTENSE CONVECTION HAS EXPLODED WITHIN 100 NM OF 19N95W WITH NUMEROUS LIGHTNING STRIKES. A COUPLE OF UNCONTAMINATED WIND BARS IN THE 30-35 KT RANGE ARE NOTED ON AN EARLIER QSCAT PASS OVER THE BAY OF CAMPECHE. SOME OF THE DEBRIS MOISTURE IS SPREADING NE WITHIN 90 NM EITHER SIDE OF LINE 21N91W TO 30N82W. CARIBBEAN SEA... AN UPPER TROUGH ENTERS THE CARIBBEAN THROUGH THE MONA PASSAGE TO NICARAGUA. AN UPPER ANTICYCLONE IS CENTERED OVER THE CAYMAN ISLANDS. AN UPPER RIDGE EXTENDS SW OVER THE SE CARIBBEAN. CURRENTLY TROPICAL STORM GUSTAV IS UNDER THE UPPER TROUGH AXIS AND WILL LATER MOVE W FURTHER AWAY FROM INFLUENCE OF LAND...AND EVENTUALLY UNDER THE INFLUENCE OF THE CAYMAN UPPER ANTICYCLONE...WHICH A MORE FAVORABLE ENVIRONMENT FOR CONTINUED DEVELOPMENT. A LINE OF SCATTERED MODERATE AND ISOLATED STRONG CONVECTION...IS ALONG 15N TO THE W OF 79W...AND EXTENDS NW TO NEAR THE YUCATAN CHANNEL. A FEW SHOWERS ARE ALSO NOTED OVER THE EXTREME NE CARIBBEAN ISLANDS. ATLANTIC OCEAN... A SERIES OF UPPER LEVEL FEATURES DOMINATE THE SUBTROPICAL N ATLANTIC. AN UPPER RIDGE EXTENDS NE FROM THE NW CARIBBEAN TO BEYOND 31N77W WITH CONVECTION ENHANCED ALONG A LINE FROM 29N76W TO 32N77W. ANOTHER UPPER ANTICYCLONE IS NEAR 29N70W WITH A FEW SHOWERS NOTED ALONG THE ITS NE PERIPHERY AT 29N67W. AN UPPER TROUGH EXTENDS SW ALONG 32N62W INTO AN UPPER CYCLONE AT 22N65W. CONVECTION IS ENHANCED E OF THE UPPER TROUGH FROM 28N62W TO BEYOND 31N58W. WEAK UPPER RIDGING IS NOTED NEAR TROPICAL STORM HANNA WITH THE DEBRIS MOISTURE FROM THE CYCLONE FANNING OUT OVER THE TROPICS WITHIN 180 NM EITHER SIDE OF LINE 14N57W TO 23N57W. A LARGE UPPER ANTICYCLONE IS NOTED OVER THE E ATLANTIC NEAR 22N26W AND IS SEPARATED FROM THE W ATLANTIC UPPER FEATURES BY AN UPPER TROUGH LYING ALONG 31N18W TO 22N22W TO 12N22W. AT THE SURFACE A 1030 MB HIGH PRESSURE IS CENTERED N OF THE AREA AT 38N30W WITH A RIDGE EXTENDING SW TO NEAR 27N54W. $$ RUBIO/NELSON