000 AXNT20 KNHC 202343 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT THU SEP 20 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 FEATURE... AN AIR FORCE RECONNAISSANCE PLANE FOUND A WELL-DEFINED AREA OF LOW PRESSURE...ANALYZED 1005 MB...CENTERED ABOUT 100 NM WSW OF TAMPA FLORIDA NEAR 27N84W. SATELLITE IMAGERY AND DOPPLER RADAR CONTINUE TO SHOW A LARGE DISORGANIZED AREA OF CLOUDINESS AND SHOWERS GENERALLY N OF 25N E OF 87W IN THE GULF OF MEXICO AND OVER AND JUST E OF FLORIDA. THE OVERALL TSTM ACTIVITY IS LIMITED AND EXTENDS ROUGHLY WITHIN 150 NM OF THE CENTER...WHICH INCLUDES W CENTRAL AND NW FLORIDA. SFC OBSERVATIONS ARE CURRENTLY REPORTING WINDS MOSTLY IN THE 15-25 KT RANGE...STRONGEST N OF THE CENTER WHERE THE PRESSURE GRADIENT IS TIGHTENED BETWEEN THE LOW AND RIDGING TO THE NW. ENVIRONMENTAL CONDITIONS ARE FAVORABLE FOR THIS SYSTEM TO BECOME A SUBTROPICAL OR TROPICAL CYCLONE AT ANY TIME DURING THE NEXT 24 HOURS. THE LOW IS FORECAST TO MOVE SLOWLY TOWARD THE WEST-NORTHWEST...AND ALL INTERESTS ALONG THE NORTHERN GULF COAST SHOULD CLOSELY MONITOR THE PROGRESS OF THIS SYSTEM. ...TROPICAL WAVES... A TROPICAL WAVE IS LOCATED JUST E OF THE CAPE VERDE ISLANDS ALONG 22W S OF 18N MOVING W 10 KT. SHOWERS AND TSTMS HAVE BEEN ON THE DECREASE OVER THE PAST SEVERAL HOURS WITH ONLY ISOLATED SHOWERS REMAINING WITHIN 45 NM OF THE WAVE AXIS. EVEN THOUGH THE WAVE LACKS CONVECTION IT STILL SHOWS UP NICELY IN THE MIMIC TPW ANIMATION AND SATELLITE DERIVED WINDS. SFC OBSERVATION FROM W AFRICA AND THE CAPE VERDE ISLANDS ALSO SHOW THE PRESCIENCE OF THIS WAVE WITH PRESSURES ABOUT 1-2 MB LOWER THAN THIS TIME YESTERDAY. A LOW AMPLITUDE TROPICAL WAVE IS ALONG 35W S OF 15N MOVING W 10-15 KT. SATELLITE IMAGERY DEPICTS THIS FEATURE AS A BROAD LOW-LATITUDE PERTURBATION WITHIN THE ITCZ. DISORGANIZED SCATTERED SHOWERS ARE WITHIN 180 NM EITHER SIDE OF THE WAVE AXIS. MORE SIGNIFICANT CONVECTION IS W OF THE WAVE EMBEDDED WITHIN THE ITCZ. TROPICAL WAVE IS ALONG 62W S OF 14N WHICH WOULD SUGGEST A MOVEMENT OF 10-15 KT OVER THE PAST 24 HOURS. HOWEVER...AS SUGGESTED IN THE PREVIOUS DISCUSSION...THIS WAVE WILL LIKELY BE PUSHED CLOSER TO 65W ON THE NEXT SYNOPTIC MAP...WHICH WOULD MEAN THIS WAVE IS MOVING 15-20 KT. THE MIMIC TPW ANIMATION TELLS THE STORY BEST SHOWING A LARGE WAVE SPITTING JUST E OF 60W. THE NRN PORTION...WHICH CONSUMED MOST OF THE ENERGY...HAS BEEN LAGGING BEHIND AND HAS MERGED WITH A SFC TROUGH IN THE REGION. THE SRN EXTENSION...WHICH IS RATHER WEAK...CONTINUES W AND IT MAY HAVE EVEN PICKED UP SOME SPEED. SCATTERED SHOWERS ARE WITHIN 90 NM OF THE CURRENT ANALYZED AXIS. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 12N16W 10N30W 8N40W 5N53W. CLUSTERS OF SCATTERED MODERATE CONVECTION IS PUSHING OFF THE W COAST OF AFRICA FROM 8N-12N CURRENTLY E OF 16W. SIMILAR CONVECTION IS WITHIN 180 NM N OF THE AXIS BETWEEN 40W-48W. DISCUSSION... GULF OF MEXICO... ATTENTION REMAINS FOCUSED ON THE DEEP LAYER LOW IN THE ERN GULF. THE ASSOCIATED DISORGANIZED SHOWER AND TSTM ACTIVITY IS GENERALLY N OF 25N E OF 87W. SEE SPECIAL FEATURE SECTION FOR DETAILS. A SWATH OF VERY DRY MID TO UPPER AIR CONTINUES TO WRAP AROUND THE PERIPHERY OF THE UPPER-LEVEL LOW THROUGH THE MIDDLE AND WESTERN GULF THEN E TO NE ACROSS THE WRN TIP OF CUBA. A NARROW DRY SLOT CONTINUES NWD ACROSS THE E PART OF THE FL PENINSULA. UPPER RIDGING...CENTERED OVER TEXAS...DOMINATES THE FAR NW PORTION WHILE A WEAKENING UPPER LOW CONTINUES TO MOVE SLOWLY OVER MEXICO NEAR 22N100W. DIFFLUENCE ALOFT E OF THIS UPPER LOW IS PRODUCING ISOLATED SHOWERS IN THE BAY OF CAMPECHE. ELSEWHERE AT THE SURFACE MODERATE RIDGING DOMINATES EXTENDING SWD FROM A 1020 MB HIGH IN THE SRN MID-WEST. CONDITIONS OVER THE NEXT COUPLE OF DAYS HIGHLY DEPEND UPON THE SPECIAL FEATURE. HOWEVER...REGARDLESS OF DEVELOPMENT...MOISTURE WILL LIKELY BE ON THE INCREASE ACROSS THE E GULF DRAWN IN BY EXTENSIVE DEEP SLY FLOW FROM THE TROPICS. CARIBBEAN SEA... A LARGE DISORGANIZED AREA OF SCATTERED SHOWERS AND ISOLATED TSTMS ARE AFFECTING MUCH OF THE REGION W OF 76W. THIS ACTIVITY IS ASSOCIATED WITH MOIST SWLY UPPER FLOW AND DIFFLUENCE ALOFT BETWEEN THE DEEP LAYER LOW IN THE GULF AND AN UPPER HIGH CENTERED OVER NICARAGUA. CONVECTION IS STRONGEST IN A PRONOUNCED DIFFLUENT ZONE FROM 14N-16N BETWEEN 76W-79W. NW TO WLY UPPER FLOW...SET UP BETWEEN THE UPPER RIDGE AND AN UPPER LOW NW OF PUERTO RICO...COVERS THE REGION E OF 80W. THIS FLOW IS VERY UNFAVORABLE FOR TROPICAL DEVELOPMENT. DRIER MID TO UPPER AIR IS OVER THE E CARIBBEAN...WITH THE EXCEPTIONS OF BROKEN CLOUDINESS AND ISOLATED SHOWERS OVER THE LESSER ANTILLES...ASSOCIATED WITH A WEAK UPPER DIFFLUENT ZONE...AND SCATTERED SHOWERS AND TSTMS OVER THE ISLAND OF HISPANIOLA. THE SURFACE PRES GRADIENT REMAINS FAIRLY RELAXED ACROSS THE AREA...DUE TO THE LOW IN THE ERN GULF AND WEAK TROUGHING IN THE WRN ATLC. THIS IS KEEPING THE TRADE WINDS MOSTLY LIGHT...EXCEPT SLIGHTLY STRONGER NEAR THE COAST OF COLOMBIA. LOOKING AHEAD...LIGHT TO MODERATE TRADES ARE EXPECTED TO PERSIST THROUGH FRI AND SHOWER ACTIVITY WILL REMAIN FOCUSED IN THE WRN CARIB. ATLANTIC OCEAN... SCATTERED SHOWERS AND TSTMS CONTINUE OVER THE WRN ATLC AND BAHAMAS W OF 71W ASSOCIATED WITH THE MOIST AND UNSTABLE ENVIRONMENT E OF THE SPECIAL FEATURE IN THE GULF...AND S OF THE STATIONARY COASTAL FRONT JUST OFFSHORE THE CAROLINAS THROUGH N FLORIDA. THE UPPER PATTERN IS ALSO CONTRIBUTING AS IT REMAINS VERY DIFFLUENT BETWEEN THE UPPER LOW OVER THE ERN GULF...AN UPPER HIGH NEAR 29N72W AND AN UPPER RIDGE IN THE CARIB. THE REMAINS OF INGRID HAVE CONTINUED TO FIZZLE TODAY...WITH A LINGERING WEAK SFC TROUGH NOW ALONG 27N66W 22N67W. THIS FEATURE IS INTERACTING WITH THE UPPER LOW JUST TO ITS W NEAR 21N68W TO PRODUCE ISOLATED SHOWERS WITHIN 60 NM OF THE AXIS. THE CENTRAL ATLC SFC PATTERN IS DOMINATED BY A 1009 MB LOW NEAR 33N48W AND ITS LONG TRAILING TROUGH WHICH EXTENDS SSW THROUGH 28N51W 17N55W. AS A SIDE NOTE...THIS BOUNDARY HAS LIKELY TEAMED UP WITH THE NRN PORTION OF THE TROPICAL WAVE IN THE E CARIB. SEE ABOVE FOR MORE DETAILS. THE LARGE SFC TROUGH...ALONG WITH ITS SUPPORTING UPPER LOW NEAR 32N48W...ARE GENERATING CLOUDINESS AND SCATTERED SHOWERS ROUGHLY WITHIN 180 NM EITHER SIDE OF THE TROUGH AXIS S OF 22N AND N OF 22N BETWEEN 40W-50W. THE REMAINDER OF THE E ATLC IS DOMINATED BY TYPICAL SFC RIDGING S OF A 1025 MB HIGH NE OF THE AZORES NEAR 40N23W. THIS IS PRODUCING MODERATE NE TRADES E OF 35W...EXCEPT STRONGER PER USUAL ALONG THE COAST OF NW AFRICA WHERE A TIGHTER GRADIENT EXISTS. A WEAK SFC TROUGH IS ASSOCIATED WITH A BENIGN UPPER LOW NEAR 29N27W WHILE UPPER RIDGING GENERALLY DOMINATES THE REMAINDER OF THE TROPICAL ATLC. LOOKING AHEAD...WEAK SFC RIDGING WILL GRADUALLY TAKE OVER THE WRN ATLC OVER THE NEXT COUPLE OF DAYS AS THE LOW IN THE GULF MOVES NW TOWARDS THE NRN GULF COAST. STRONGER RIDGING IS EXPECTED TO CHANGE LITTLE IN THE E ATLC. THE LOW PRES SYSTEM IN THE CENTRAL ATLC IS NOT EXPECTED TO MOVE VERY MUCH KEEPING A PRONOUNCED WEAKNESS IN THE SUBTROPICAL RIDGE. $$ CANGIALOSI