000 AXNT20 KNHC 211806 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT FRI SEP 21 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...SPECIAL FEATURE... SATELLITE IMAGERY INDICATES THAT THE SUBTROPICAL DEPRESSION OVER THE NE GULF HAS ACQUIRED ENOUGH TROPICAL CHARACTERISTICS TO BE CONSIDERED A TROPICAL DEPRESSION. A TROPICAL STORM WARNING IS IN EFFECT FROM APALACHICOLA FLORIDA WESTWARD TO THE MOUTH OF THE MISSISSIPPI RIVER...INCLUDING NEW ORLEANS AND LAKE PONTCHARTRAIN. AS OF 100 PM CDT...1800 UTC...THE CENTER OF TROPICAL DEPRESSION TEN WAS LOCATED NEAR 29.7N 85.9W...OR ABOUT 40 NM SW OF APALACHICOLA FLORIDA AND ABOUT 135 NM E-SE OF MOBILE ALABAMA. THE DEPRESSION IS MOVING NW NEAR 10 KT. A TURN TO THE W-NW IS EXPECTED OVER THE NEXT 24 HOURS. ON THE FORECAST TRACK...THE CENTER OF THE DEPRESSION WILL BE MOVING NEARLY PARALLEL TO THE COASTLINE WITHIN THE WARNING AREA TODAY AND TONIGHT. MAXIMUM SUSTAINED WINDS ARE NEAR 30 KT WITH GUSTS TO 40 KT. THE DEPRESSION IS EXPECTED TO BECOME A TROPICAL STORM LATER TODAY OR TOMORROW. PLEASE REFER TO THE LATEST NHC FORECAST ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT5/WTNT25 KNHC AND THE PUBLIC ADVISORY UNDER MIATCPAT5/WTNT35 KNHC FOR MORE DETAILS. RADAR IMAGERY SHOWS BROKEN UP BANDS OF SCATTERED SHOWERS AND TSTMS SPREADING INLAND THROUGH THE FLORIDA PANHANDLE FROM THE NE GULF. ISOLATED TORNADOES ARE POSSIBLE OVER SOUTHWESTERN GEORGIA...THE FLORIDA PANHANDLE...AND SOUTHEASTERN ALABAMA THROUGH TONIGHT. IN ADDITION TO THIS THREAT...RIP CURRENTS AND ROUGH SURF WILL BE A PROBLEM ALONG PORTIONS OF THE GULF COAST. SEE STATEMENTS FROM LOCAL WEATHER SERVICE OFFICES FOR MORE DETAILS. ...TROPICAL WAVES... A TROPICAL WAVE IS MOVING ACROSS THE CAPE VERDE ISLANDS WITH THE AXIS TILTED ALONG 18N26W 6N24W MOVING W NEAR 10 KT. THIS WAVE CONTINUES TO SHOW UP WELL IN LOW LEVEL SATELLITE DERIVED WINDS AND THE UW-CIMSS TPW PRODUCT. HOWEVER...DEEP CONVECTION IS ALMOST NON EXISTENT NEAR THIS FEATURE WITH ONLY A FEW SHALLOW ISOLATED SHOWERS NOTED IN THE VICINITY. A LOW AMPLITUDE TROPICAL WAVE IS ALONG 37W S OF 15N MOVING W 10-15 KT. SATELLITE IMAGERY DEPICTS THIS FEATURE AS A BROAD LOW-LATITUDE PERTURBATION WITHIN THE ITCZ...AND THE AXIS PLACEMENT IS LOCATED WHERE THE MOST POLEWARD INFLECTION OF THE ITCZ IS NOTED. SCATTERED MODERATE CONVECTION IS OVER MUCH OF THE VICINITY FROM 7N-12N BETWEEN 35W-44W...ASSOCIATED WITH THE WAVE INTERACTING WITH THE ITCZ. A WEAK TROPICAL WAVE IS OVER CARIBBEAN ALONG 70W S OF 18N MOVING W 15-20 KT. THE MIMIC TPW ANIMATION SHOWS THE PRESENCE OF THE WAVE AS A LOW AMPLITUDE SURGE OF MOISTURE MOVING THROUGH THE ABC ISLANDS. HOWEVER...MINIMAL SHOWER ACTIVITY IS NOTED NEAR THIS FEATURE. OVER THE LAST COUPLE OF DAYS...SOME OF THE ENERGY ASSOCIATED WITH THIS WAVE BECAME DETACHED ENE OF THE LEEWARD ISLANDS OVER THE TROPICAL ATLC. IN FACT...A WEAK LOW PRESSURE AREA APPEARS TO BE SPINNING NEAR 17.7N56W AND MAY BE ADDED TO FUTURE MAPS. ...THE ITCZ... AXIS IS CENTERED ALONG 7N12W 10N22W 8N30W 11N37W 8N46W 4N53W. SCATTERED SHOWERS AND TSTMS ARE MOSTLY S OF THE AXIS FROM 3N-8N BETWEEN 15W-20W. ISOLATED MODERATE CONVECTION IS WITHIN 150NM N/60NM S OF THE AXIS BETWEEN 28W-34W. A BROAD AREA OF SCATTERED SHOWERS AND TSTMS ARE ASSOCIATED WITH BOTH THE ITCZ AND TROPICAL WAVE ALONG 37W FROM 6N-13N BETWEEN 35W-52W. DISCUSSION... GULF OF MEXICO... ALL THE ATTENTION THIS AFTERNOON REMAINS FOCUSED ON NEWLY FORMED TROPICAL DEPRESSION TEN. SEE SPECIAL FEATURE SECTION ABOVE FOR MORE DETAILS. A TRAILING TROUGH EXTENDS SW FROM THE DEPRESSION THROUGH 27N87W 22N90W. SCATTERED SHOWER/ISOLATED TSTMS ARE GENERALLY OVER MUCH OF THE NE GULF E OF 90W. DRY AIR/SUBSIDENCE IS SPREADING S THROUGH THE WRN GULF N OF 20N W OF 90W...ON THE W SIDE OF THE FRAGMENTING UPPER LOW NOW JUST SW OF TROPICAL DEPRESSION TEN. A SWATH OF DRY AIR CONTINUES TO ROTATE AROUND THE PERIPHERY OF THE UPPER LOW...MOVING NE BETWEEN A POINT JUST N OF THE YUCATAN CHANNEL NEAR 23N87W TO JUST N OF TAMPA NEAR 28N82W. TROPICAL MOISTURE FROM THE EPAC IS OVER THE BAY OF CAMPECHE S OF 20N WITH UPPER SW FLOW AHEAD OF TROUGHING. SFC WINDS ARE MUCH LIGHTER IN THE WRN GULF W OF 91W WITH A WEAKER GRADIENT IN PLACE WELL W OF THE DEPRESSION. THE DEPRESSION IS EXPECTED TO MOVE INLAND...POSSIBLY AS A TROPICAL STORM...BY SATURDAY EVENING. HOWEVER...TRAILING MOISTURE SPREADING N FROM THE CARIBBEAN IS EXPECTED TO KEEP SCATTERED SHOWER/TSTM ACTIVITY OVER PORTIONS OF THE ERN AND MIDDLE GULF THROUGH THE WEEKEND. IN FACT...GFS CONTINUES TO DEVELOP A WEAK LOW IN THE FAR NW CARIBBEAN AND MOVE IT THROUGH THE YUCATAN BY LATE THIS WEEKEND...BUT THERE IS CURRENTLY LOW CONFIDENCE IN THIS SCENARIO. CARIBBEAN SEA... CLUSTERS OF MODERATE TO ISOLATED STRONG CONVECTION PERSIST OVER THE WESTERN CARIBBEAN WEST OF 76W. THIS ACTIVITY IS ASSOCIATED WITH A SFC TROUGH THAT RUNS FROM 17N83W TO 11N76W AND A DIFFLUENT PATTERN ALOFT RELATED TO AN UPPER RIDGE THAT COVERS MOST OF THE WEST AND CENTRAL CARIBBEAN. THE SFC CONVERGENCE THAT IS RESPONSIBLE FOR THE SFC TROUGH IS ASSOCIATED WITH THE DEEP SLY FLOW AHEAD OF THE DEPRESSION OVER THE NE GULF COLLIDING WITH THE MORE TYPICAL TRADES FROM THE ERN AND CENTRAL CARIBBEAN. DEVELOPMENT OF THIS SYSTEM...IF ANY...IS EXPECTED TO BE SLOW TO OCCUR AS IT MOVES SLOWLY WESTWARD. UPPER TROUGHING...LIGHT TO MODERATE TRADES...AND MOSTLY SHALLOW...ISOLATED SHOWER ACTIVITY DOMINATES THE E AND CENTRAL CARIBBEAN E OF 76W. ATLANTIC OCEAN... SCATTERED SHOWERS AND TSTMS CONTINUE OVER THE WRN ATLC AND THE BAHAMAS W OF 74W ASSOCIATED WITH THE MOIST AND UNSTABLE ENVIRONMENT E OF DEEP LAYERED LOW PRESSURE IN THE EASTERN GULF AND S OF THE STATIONARY COASTAL FRONT JUST OFFSHORE THE CAROLINAS AND GEORGIA. UPPER DIFFLUENCE BETWEEN THE UPPER LOW OVER THE ERN GULF AND AN UPPER HIGH NEAR 27N72W IS ALSO SUPPORTING THIS CONVECTIVE ACTIVITY. A WEAK SFC TROUGH ASSOCIATED WITH THE REMNANTS OF INGRID EXTENDS ALONG 29N66W 23N68W. ONLY ISOLATED SHOWERS ARE NEAR THE TROUGH AXIS. THIS FEATURE IS INTERACTING WITH THE UPPER LOW LOCATED JUST N OF HISPANIOLA. THE CENTRAL ATLC SFC PATTERN IS DOMINATED BY A 1010MB LOW NEAR 34N47W OR ABOUT 950 NM EAST OF BERMUDA. THIS NON-TROPICAL LOW HAS CHANGED LITTLE SINCE YESTERDAY...BUT IS STILL BEING MONITORED FOR SIGNS OF TROPICAL DEVELOPMENT. A SFC TROUGH EXTENDS FROM THE LOW ALONG 28N47W 22N54W 15N55W. SCATTERED MODERATE CONVECTION IS MOSTLY WITHIN 180 NM E OF THE TROUGH AXIS. AS MENTIONED IN THE TROPICAL WAVE SECTION...SOME OF THE SRN PORTION OF THE TROUGHING MAY HAVE GAINED ENERGY FROM THE WAVE NOW MOVING THROUGH THE CARIBBEAN NEAR 70W. THE REMAINDER OF THE E ATLC IS DOMINATED BY TYPICAL SFC RIDGING S OF A 1027 MB HIGH E OF THE AZORES NEAR 38N21W. THIS IS PRODUCING MODERATE NE TRADES E OF 35W...EXCEPT STRONGER NEAR THE COAST OF NW AFRICA WHERE A TIGHTER PRES GRADIENT EXISTS. IN FACT...SHIP ZCDE4 WAS REPORTING NE WINDS OF 30 KT NEAR 25N17W WITH SEAS OF 9 FT THIS MORNING. THE UPPER LOW OVER THE ERN ATLC NEAR 28N26W APPEARS TO BE GENERATING A LITTLE MORE SENSIBLE WEATHER TODAY...WITH POTENTIAL SCATTERED SHOWER ACTIVITY FALLING OUT OF THE COLDER CLOUD TOPS NOTED N OF 24N BETWEEN 19W-26W. WEAK SFC RIDGING WILL GRADUALLY TAKE OVER THE WRN ATLC OVER THE NEXT COUPLE OF DAYS WHILE STRONGER RIDGING CONTINUES TO SIT OVER THE E ATLC. CONFLUENCE BETWEEN THE SFC RIDGES WILL ALLOW BROAD TROUGHING AND SCATTERED SHOWER ACTIVITY TO PERSIST OVER PARTS OF THE CENTRAL ATLC MAINLY N OF 18N...AND S OF THE NON-TROPICAL SYSTEM BEING MONITORED WELL E OF BERMUDA. $$ WILLIS