ZCZC MIATCDAT2 ALL TTAA00 KNHC DDHHMM HURRICANE OLGA DISCUSSION NUMBER 13 NATIONAL WEATHER SERVICE MIAMI FL 4 PM EST TUE NOV 27 2001 OLGA REMAINS QUITE IMPRESSIVE IN SATELLITE IMAGERY AND THE EYE...PLUS THE EYEWALL CONVECTION...HAVE BECOME MORE DISTINCT DURING THE PAST 3 HOURS. THE INITIAL INTENSITY WAS BUMPED UP SLIGHTLY TO 80 KT BASED ON CONSENSUS SATELLITE INTENSITY ESTIMATES OF T4.5...77 KT...FROM ALL THREE AGENCIES...AND THE IMPROVED INNER- CORE CONVECTIVE PATTERN. UPPER-LEVEL OUTFLOW IS CONFINED PRIMARILY TO THE NORTH...BUT HAS BEEN IMPROVING TO THE SOUTH. THE INITIAL MOTION ESTIMATE IS 010/10. HOWEVER...OLGA HAS BEEN MAKING A RATHER LARGE CYCLONIC LOOP DURING THE PAST 18 HOURS. THE CYCLONE REMAINS EMBEDDED IN THE LARGER-SCALE MID- TO UPPER-LEVEL LOW/TROUGH PATTERN. A SERIES OF SHARP VORTICITY CENTERS HAVE BEEN TRACKING AROUND THE SOUTHERN AND EASTERN PERIPHERY OF OLGA...WHICH HAS RESULTED IN BINARY INTERACTION MOTION. THE LATEST AND POSSIBLY LAST STRONG VORTICITY MAXIMUM IS LOCATED ABOUT 400 NM EAST OF OLGA AND HAS BEEN HELPING TO LIFT THE SYSTEM NORTHWARD DURING THE PAST 6 HOURS. OLGA AND THE VORTICITY CENTER SHOULD SEPARATE DURING THE NEXT 6 TO 12 HOURS...WHICH SHOULD ALLOW FOR OLGA TO SLOW DOWN AND GRADUALLY TURN BACK TO THE WEST AND EVENTUALLY TO THE SOUTHWEST. THE STRONG DEVELOPING WINTER STORM OVER THE SOUTHERN PLAINS IS EXPECTED TO LIFT OUT TO THE NORTHEAST DURING THE NEXT 72 HOURS WHICH SHOULD HELP TO BUILD THE MID- AND UPPER-LEVEL RIDGE TO THE NORTH OF THE OLGA. ALL OF THE GLOBAL MODELS AGREE ON THE SAME GENERAL SYNOPTIC PATTERN DEVELOPING THROUGHOUT THE FORECAST PERIOD AND TAKE THE CYCLONE TO THE SOUTHWEST...ALBEIT AT SIGNIFICANTLY DIFFERENT FORWARD SPEEDS. NOGAPS AND THE UKMET ARE THE FASTEST WHILE THE GFDL AND AVN ARE THE SLOWEST OF THE MODELS. THE AVN-GFDL SOLUTION USES A DEEPER LAYER STEERING FLOW...WHEREAS THE WEAKER UKMET-NOGAPS SOLUTIONS ALLOW FOR A SHALLOW SYSTEM TO BE STEERED RAPIDLY WESTWARD BY STRONG LOW-LEVEL EASTERLY STEERING FLOW. THE OFFICIAL FORECAST IS CLOSE TO THE SLOWER AVN-GFDL CONSENSUS SINCE THOSE TWO MODELS DO NOT WEAKEN OLGA AS QUICKLY AS THE NOGAPS AND UKMET MODELS. THE INTENSITY FORECAST IS A LITTLE TRICKY GIVEN THE COLD SSTS AND THE COLD MID- AND UPPER-LEVEL ENVIRONMENT SURROUNDING OLGA. THERE IS NOT MUCH INTENSITY GUIDANCE AVAILABLE FOR THESE "COLD" TROPICAL CYCLONES. THE SHIPS INTENSITY MODEL WEAKENS OLGA STEADILY THROUGH THE PERIOD AND BRINGS THE SYSTEM BELOW HURRICANE STRENGTH IN 24 TO 36 HOURS AND DOWN TO 50 KT IN 72 HOURS. HOWEVER...THE MAIN NEGATIVE CONTRIBUTING FACTOR IN THE MODEL IS THE COOLER THAN NORMAL SSTS. ALTHOUGH OLGA IS CURRENTLY OVER SUB-24C SSTS...THE SURROUNDING ENVIRONMENT IS ALSO MUCH COLDER THAN THE TYPICAL TROPICAL ATMOSPHERE. SINCE THERE IS AVAILABLE INSTABILITY AND LOW SHEAR...LESS THAN 15 KT...FORECAST THROUGHOUT THE PERIOD...OLGA SHOULD REMAIN A SIGNIFICANT TROPICAL CYCLONE FOR AT LEAST THE NEXT FEW DAYS. THE OFFICIAL INTENSITY CALLS FOR ONLY SLOW WEAKENING TO BEGIN BY 36 HOURS...AFTER WHICH SOME MID-LEVEL DRY AIR FROM THE NORTH MAY GET ENTRAINED INTO THE SYSTEM. LARGE SWELLS WILL CONTINUE TO AFFECT MOST OF THE MAJOR LAND AREAS AND ISLANDS FROM THE U.S. EAST COAST TO THE CARIBBEAN ISLANDS. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 27/2100Z 32.3N 55.9W 80 KTS 12HR VT 28/0600Z 33.1N 55.9W 80 KTS 24HR VT 28/1800Z 32.0N 56.4W 80 KTS 36HR VT 29/0600Z 30.9N 56.9W 75 KTS 48HR VT 29/1800Z 30.0N 57.4W 70 KTS 72HR VT 30/1800Z 28.5N 59.0W 65 KTS NNNN