691 
 WTNT41 KNHC 110234
 TCDAT1
 TROPICAL STORM IGOR DISCUSSION NUMBER  11
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
 1100 PM AST FRI SEP 10 2010
  
 CONVENTIONAL SATELLITE IMAGES INDICATE THAT IGOR IS MAINTAINING A
 BURSTING PATTERN...CHARACTERISTIC OF A SHEARED TROPICAL CYCLONE. 
 THE PARTIALLY EXPOSED LOW-LEVEL CENTER LIES NEAR THE NORTHEAST SIDE
 OF A LARGE AND CIRCULAR CONVECTIVE MASS IN THIS IMAGERY...BUT
 SEVERAL EARLIER MICROWAVE OVERPASSES INDICATED THE POSSIBILITY OF
 THE LOW-LEVEL CENTER LYING UNDERNEATH THE CONVECTION.  AN EXPANDING
 UPPER-LEVEL OUTFLOW IS WELL ESTABLISHED IN ALL QUADRANTS EXCEPT TO
 THE EAST.  DVORAK INTENSITY ESTIMATES ARE AT 3.0/45 KT AND 3.5/55
 KT FROM SAB AND TAFB...AND THE LATEST 3-HOURLY AVERAGED ADT VALUE
 IS 3.3.  GIVEN THE UNCERTAINTY WITH REGARD TO THE LOCATION OF THE
 CENTER...THE ADVISORY INTENSITY IS INCREASED CONSERVATIVELY TO 45
 KT.
  
 THE INITIAL MOTION ESTIMATE OF 285/18 IS SOMEWHAT UNCERTAIN AND
 REPRESENTS A LONGER-TERM AVERAGE...GIVEN DIFFERENCES BETWEEN
 CONVENTIONAL AND MICROWAVE SATELLITE FIXES. THE FORECAST REASONING
 REMAINS UNCHANGED. DYNAMICAL MODELS SHOW IGOR MOVING ON A WESTWARD
 COURSE ON THE SOUTH SIDE OF A SUBTROPICAL RIDGE OVER THE EAST
 CENTRAL ATLANTIC DURING THE NEXT 72 HOURS.  DURING THIS
 PERIOD...THE MODEL GUIDANCE IS IN GOOD AGREEMENT THAT IGOR SHOULD
 SLOW ITS FORWARD SPEED AND THEN TURN WEST-NORTHWESTWARD BEYOND 72
 HOURS IN RESPONSE TO A LARGE BREAK IN THE SUBTROPICAL RIDGE OVER
 THE WESTERN AND CENTRAL ATLANTIC.  THE OFFICIAL NHC TRACK LIES NEAR
 THE MIDDLE OF THE GUIDANCE ENVELOPE...BUT IS A BIT NORTH OF THE
 MULTI-MODEL CONSENSUS WHICH HAS TRENDED SLIGHTLY SOUTHWARD THIS
 CYCLE.
  
 UW-CIMSS ANALYSES STILL INDICATE AROUND 15 KT OF NORTHEASTERLY
 VERTICAL WIND SHEAR OVER IGOR...A LESS THAN IDEAL ENVIRONMENT FOR
 INTENSIFICATION.  THE STATISTICAL-DYNAMICAL GUIDANCE INDICATES A
 QUICK REDUCTION TO THE SHEAR DURING THE NEXT 24 HOURS...AND A LOW
 SHEAR ENVIRONMENT OVER GRADUALLY WARMER WATERS ARE LIKELY TO LEAD
 TO A STEADIER STRENGTHENING OVER THE NEXT COUPLE OF DAYS.  THE
 INTENSITY GUIDANCE PRESENTS A DILEMMA LATER IN THE FORECAST
 PERIOD...HOWEVER.  THE STATISTICAL MODEL OUTPUT INDICATES POSSIBLE
 SOUTHWESTERLY SHEAR RELATED TO THE LONGWAVE TROUGH FORECAST OVER
 THE WEST CENTRAL ATLANTIC...AS DO A FEW OF THE GLOBAL DYNAMICAL
 MODELS.  ON THE OTHER HAND...THE HWRF AND ECMWF SOLUTIONS A
 CONTINUATION OF THE LOW SHEAR ENVIRONMENT AND A STRONGER IGOR.  THE
 OFFICIAL NHC INTENSITY FORECAST IS ABOUT THE SAME AS THE PREVIOUS
 ONE...EXCEPT SLIGHTLY REDUCED LATE IN THE PERIOD IN DEFERENCE TO
 THE STATISTICAL MODELS.
  
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      11/0300Z 17.1N  34.9W    45 KT
  12HR VT     11/1200Z 17.2N  37.2W    50 KT
  24HR VT     12/0000Z 17.4N  40.1W    55 KT
  36HR VT     12/1200Z 17.5N  42.8W    65 KT
  48HR VT     13/0000Z 17.6N  45.3W    75 KT
  72HR VT     14/0000Z 18.0N  49.5W    85 KT
  96HR VT     15/0000Z 19.0N  53.0W    90 KT
 120HR VT     16/0000Z 20.5N  56.0W   100 KT
  
 $$
 FORECASTER KIMBERLAIN