000 WTNT41 KNHC 240255 TCDAT1 TROPICAL STORM OPHELIA DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL AL162011 1100 PM AST FRI SEP 23 2011 EASY COME...EASY GO. AFTER STRENGTHENING EARLIER THIS AFTERNOON... OPHELIA NOW APPEARS TO BE ON A WEAKENING TREND. AN AIR FORCE HURRICANE HUNTER AIRCRAFT INVESTIGATING THE SYSTEM MEASURED A MAXIMUM 925-MB FLIGHT-LEVEL WIND OF 47 KT AND HAS YET TO MEASURE ANY TROPICAL-STORM-FORCE WINDS FROM THE SFMR. IN ADDITION...THE LAST CENTRAL PRESSURE MEASURED BY THE PLANE WAS 1006 MB. HOWEVER...THE PLANE IS JUST GETTING READ TO SAMPLE THE DEEP CONVECTION LOCATED ABOUT 100-200 N MI NORTHEAST OF THE LOW-LEVEL CENTER...AND THE INITIAL INTENSITY IS ONLY BEING LOWERED TO 45 KT FOR NOW UNTIL WE CAN GET DATA FROM THAT PART OF THE STORM. STRONG SOUTHWESTERLY SHEAR IS EXPECTED TO CONTINUE AFFECTING OPHELIA FOR AT LEAST THE NEXT 3 DAYS. AFTER THAT...THE POSITION OF THE CYCLONE RELATIVE TO THE UPPER-LEVEL TROUGH TO ITS NORTHWEST WILL MEAN THE DIFFERENCE BETWEEN A HOSTILE OR FAVORABLE ENVIRONMENT FOR STRENGTHENING. GIVEN THE UNCERTAINTY...IT IS NOT WORTH HAGGLING OVER 5 OR 10 KT FROM DAY TO DAY...AND THE OFFICIAL FORECAST HOLDS THE INTENSITY CONSTANT THROUGH 5 DAYS WITH THE UNDERSTANDING THAT FLUCTUATIONS ARE LIKELY. BASED ON RECENT FIXES FROM THE PLANE...THE CENTER OF OPHELIA IS EITHER JUMPING AROUND OR IS BECOMING LESS WELL DEFINED. A 12-HOUR AVERAGE GIVES A MOTION OF 300/12. OPHELIA IS FORECAST TO TURN NORTHWESTWARD IN THE NEXT 12 HOURS OR SO AND SHOULD BEGIN TO DECREASE IN FORWARD SPEED AS IT BECOMES BLOCKED BY THE MID-LEVEL HIGH TO ITS NORTH. THE GUIDANCE ENVELOPE HAS SHIFTED SOMEWHAT SIGNIFICANTLY TO THE EAST WITH A SLOWER MOTION AND IS BOUNDED BY THE WESTERNMOST ECMWF AND THE EASTERNMOST HWRF AND GFDL. THE NEW OFFICIAL FORECAST HAS BEEN SHIFTED EASTWARD AND LIES ON THE WESTERN EDGE OF THE MAIN CLUSTER OF MODELS...CLOSE TO THE ECMWF. IT SHOULD BE NOTED THAT SOME OF THE MODELS ARE SHOWING A SLOW NORTHEASTWARD MOTION BY DAY 5...BUT THAT SCENARIO IS NOT YET INDICATED BY THE OFFICIAL FORECAST. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 16.0N 54.5W 45 KT 50 MPH 12H 24/1200Z 16.9N 56.1W 45 KT 50 MPH 24H 25/0000Z 18.2N 58.0W 45 KT 50 MPH 36H 25/1200Z 19.4N 59.7W 45 KT 50 MPH 48H 26/0000Z 20.3N 61.1W 45 KT 50 MPH 72H 27/0000Z 22.0N 63.5W 45 KT 50 MPH 96H 28/0000Z 24.0N 64.5W 45 KT 50 MPH 120H 29/0000Z 26.0N 65.0W 45 KT 50 MPH $$ FORECASTER BERG