000 AXNT20 KNHC 161750 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT THU OCT 16 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... HURRICANE OMAR IS QUICKLY WEAKENING AS IT MOVES RAPIDLY AWAY FROM THE NORTHERN LEEWARD ISLANDS. HEAVY RAINFALL THREAT REMAINS FOR THE NORTHERN AND CENTRAL LESSER ANTILLES. AT 16/1500 UTC... OMAR IS CENTERED NEAR 20.2N 61.3W OR ABOUT 155 NM...290 KM... NORTHEAST OF THE NORTHERN LEEWARD ISLANDS MOVING NE OR 035 DEG AT 20 KT. THIS GENERAL MOTION IS EXPECTED DURING THE NEXT TWO DAYS. ESTIMATED MINIMUM CENTRAL PRESSURE IS 980 MB. MAXIMUM SUSTAINED WIND SPEED HAS DECREASED TO 75 KT WITH GUSTS TO 90 KT. PLEASE SEE LATEST NHC PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT5/WTNT35 KNHC AND THE FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT5/WTNT25 KNHC FOR MORE DETAILS. OMAR REACHED NEAR THE THRESHOLD OF CATEGORY 4 EARLY THIS MORNING AROUND 06Z. A FEW HOURS LATER...VISIBLE SATELLITE IMAGERY REVEALED AN EXPOSED LOW-LEVEL CENTER INDICATING A RAPIDLY WEAKENING TREND OF THIS CYCLONE. BANDS OF MODERATE TO ISOLATED STRONG CONVECTION...ASSOCIATED WITH THE OVERALL CIRCULATION OF OMAR...CONTINUES TO AFFECT THE NORTHERN AND CENTRAL LESSER ANTILLES AND THE FAR EASTERN CARIBBEAN SEA MAINLY E OF 64W. ST. THOMAS REPORTED THIS MORNING 2.42 INCHES OF RAIN IN 24 HOURS. ...TROPICAL WAVES... A TROPICAL WAVE IS MOVING ACROSS THE CAPE VERDE ISLANDS. ITS AXIS IS ALONG 23W/24W S OF 18N MOVING W NEAR 10-15 KT. CYCLONIC CURVATURE IS EVIDENT ON SATELLITE IMAGERY WITH CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION MAINLY BEHIND THE WAVE AXIS FROM 11N-15N AND BETWEEN 22W-25W. AN ACTIVE TROPICAL WAVE IS ALONG 45W S OF 14N MOVING W NEAR 10 KT. THE WAVE SHOWS A CLASSIC INVERTED-V PATTERN ON SATELLITE IMAGERY WITH SCATTERED TO NUMEROUS MODERATE TO ISOLATED STRONG CONVECTION WITHIN 180-200 NM EITHER SIDE OF THE WAVE AXIS FROM 8N-12N. ...THE ITCZ... THE ITCZ IS PRETTY ACTIVE TODAY. ITS AXIS IS CENTERED ALONG 8N13W 6N30W 8N42W 6N50W 9N61W. IN ADDITION TO CONVECTION ASSOCIATED WITH THE TROPICAL WAVES...SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 125 NM N OF AXIS BETWEEN 25W-41W. SIMILAR CONVECTION IS WITHIN 100 NM SOUTH OF AXIS BETWEEN 35W-41W. ...DISCUSSION... GULF OF MEXICO... AN UPPER-LEVEL LOW REMAINS INLAND OVER NORTH-CENTRAL MEXICO NEAR 24N100W. AN BROAD UPPER-LEVEL RIDGE ANCHORED ON A HIGH JUST N OF THE YUCATAN PENINSULA COVERS MOST OF THE GULF REGION AND THE FLORIDA PENINSULA EXTENDING ALSO OVER THE WESTERN ATLC...THE BAHAMAS AND CUBA INTO THE NW CARIBBEAN. MOIST SLY WIND FLOW BETWEEN THESE TWO UPPER-LEVEL FEATURES ALONG WITH A SURFACE TROUGH EXTENDING ALONG 93W ARE GENERATING SCATTERED SHOWERS AND ISOLATED TSTMS OVER THE WRN GULF W OF 93W AND THE WESTERN BAY OF CAMPECHE. A COLD FRONT HAS ENTERED THE FAR NW GULF AND EXTENDS FROM A WEAK 1020 MB LOW OVER NW LOUISIANA THROUGH THE DEEP SOUTH TEXAS INTO THE NE PORTION OF MEXICO. MOSAIC DOPPLER RADAR FROM THE SE U.S. DEPICTS A NARROW BAND OF SHOWERS WITH EMBEDDED TSTMS ASSOCIATED WITH THE FRONT WHICH IS FORECAST TO MOVE SE ACROSS THE REGION DURING THE NEXT FEW DAYS INCREASING WINDS AND SEAS. THE FRONT WILL MOVE ACROSS SOUTH FLORIDA LATE SAT NIGHT AND EARLY SUN...AND WILL LIKELY BECOME DIFFUSE FROM THE STRAITS OF FLORIDA TO BAY OF CAMPECHE LATE SUN. HIGH PRESSURE CENTERED OVER THE SE CONUS DOMINATES MUCH OF THE GULF E OF 90W...INCLUDING THE FLORIDA PENINSULA AND STRAITS OF FLORIDA. STRONG SUBSIDENCE/DRY AIR IS ALSO NOTED IN THE UPPER-LEVELS E OF 90W IN THE GULF. HIGH PRES WILL BUILD IN BEHIND THE COLD FRONT. CARIBBEAN SEA... HURRICANE OMAR IS MOVING AWAY FROM THE NORTHERN LEEWARD ISLANDS BUT IT IS STILL PRODUCING LOCALLY HEAVY RAIN OVER PORTIONS OF THE NORTHERN AND CENTRAL LESSER ANTILLES FROM ANTIGUA SOUTHWARD TO MARTINIQUE WHERE ADDITIONAL RAINFALL AMOUNTS OF 1 TO 3 INCHES... WITH MAXIMUM AMOUNTS UP TO 6 INCHES ARE EXPECTED. SEE SPECIAL FEATURES FOR MORE DETAILS. THE REMNANT CIRCULATION OF FORMER TROPICAL DEPRESSION SIXTEEN PERSIST OVER NORTHERN HONDURAS WITH MOST OF THE SHOWER ACTIVITY AFFECTING SOUTHERN BELIZE AND PARTS OF GUATEMALA AND HONDURAS. A 1008 MB LOW WAS ANALYZED NEAR 16N86W ON THE 12Z SURFACE MAP. ALTHOUGH REFORMATION OF A TROPICAL CYCLONE WILL NOT OCCUR DUE TO LAND INTERACTION...THIS SYSTEM COULD STILL PRODUCE BRIEF PERIODS OF STRONG GUSTY WINDS... ESPECIALLY OVER THE GULF OF HONDURAS...ALONG WITH LOCALLY HEAVY RAINFALL. THESE RAINS COULD CAUSE FLASH FLOODS ACROSS PORTIONS OF NICARAGUA...HONDURAS...EL SALVADOR...BELIZE...AND GUATEMALA DURING THE NEXT COUPLE OF DAYS AS THE SYSTEM MOVES WESTWARD AT AROUND 5 KT. A SFC TROUGH EXTENDS FROM HURRICANE OMAR ACROSS THE EASTERN CARIBBEAN TO JUST NORTH OF THE ABC ISLANDS. ISOLATED TO SCATTERED SHOWERS ARE RELATED TO THIS FEATURE EAST OF 72W. SCATTERED MODERATE CONVECTION IS OVER THE SW CARIBBEAN SOUTH OF 13N BETWEEN 75W-83W. UPPER DIFFLUENCE IS HELPING TO INDUCE THIS ACTIVITY. AS PREVIOUSLY MENTIONED...THE UPPER-LEVEL HIGH LOCATED JUST NORTH OF THE YUCATAN PENINSULA EXTENDS A RIDGE OVER THE WRN CARIBBEAN SEA AND CENTRAL AMERICA S TO PANAMA AND CONTINUES TO ENHANCE CONVECTION OVER THE AREA. WATER VAPOR IMAGERY REVEALS A DEEP LAYERED TROUGH ACROSS THE W ATLC DIGGING SWD INTO THE CENTRAL CARIBBEAN THROUGH HISPANIOLA. THIS TROUGH IS PRODUCING STRONG VERTICAL SHEAR OVER OMAR AND WILL LIKELY CONTINUE TO CAUSE A DECREASE IN ITS INTENSITY. PATCHES OF LOW LEVEL CLOUDS WITH POSSIBLE SHOWERS ARE REACHING PART OF CUBA AS WELL AS HISPANIOLA AND PUERTO RICO UNDER A NLY WIND FLOW. ATLANTIC OCEAN... THE UPPER-LEVEL RIDGE CENTERED OVER THE GULF OF MEXICO ENVELOPS THE W ATLC WATERS AND THE BAHAMAS W OF 70W. STRONG SUBSIDENCE IS ASSOCIATED WITH THIS UPPER RIDGE BRINGING DRY AIR ACROSS THE FLORIDA PENINSULA...THE BAHAMAS AND CUBA. A DEEP LAYERED TROUGH EXTENDING FROM AN UPPER-LEVEL LOW LOCATED NEAR 33N59W ENTERS THE CARIBBEAN SEA THROUGH HISPANIOLA. THE BASE OF THE TROUGH IS REACHING 16N. THIS UPPER TROUGH SUPPORTS A SURFACE TROUGH THAT EXTENDS FROM A 1008 MB LOW LOCATED NEAR 30N60W TO JUST NORTH OF HURRICANE OMAR NEAR 23N61W. THIS LOW IS FORECAST TO DISSIPATE IN ABOUT 24 HOURS. THE REMAINDER OF THE FORECAST AREA IS UNDER THE INFLUENCE OF A SFC RIDGE ANCHORED ON A 1031 MB HIGH NEAR THE AZORES. ALOFT...A RIDGE/TROUGH/RIDGE PATTERN IS SEEN OVER THE CENTRAL AND EASTERN ATLC WITH RIDGES CENTERED NEAR 18N52W AND INLAND OVER WEST AFRICA. BOTH RIDGES ARE SUPPORTING CONVECTION ALONG THE ITCZ AXIS. $$ GR