000WTNT31 KNHC 291446TCPAT1BULLETINTROPICAL STORM OPHELIA ADVISORY NUMBER 28NWS NATIONAL HURRICANE CENTER MIAMI FL AL1620111100 AM AST THU SEP 29 2011...OPHELIA ALMOST A HURRICANE...SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION-----------------------------------------------LOCATION...20.9N 61.8WABOUT 205 MI...330 KM NNE OF THE NORTHERN LEEWARD ISLANDSMAXIMUM SUSTAINED WINDS...70 MPH...110 KM/HPRESENT MOVEMENT...NNW OR 335 DEGREES AT 9 MPH...15 KM/HMINIMUM CENTRAL PRESSURE...991 MB...29.26 INCHES
000WTNT41 KNHC 300844TCDAT1HURRICANE OPHELIA DISCUSSION NUMBER 31NWS NATIONAL HURRICANE CENTER MIAMI FL AL162011500 AM AST FRI SEP 30 2011OPHELIA HAS BEEN RAPIDLY STRENGTHENING DURING THE PAST 12 HOURSBASED ON AN EYE FEATURE OCCASIONALLY APPARENT ON BOTH INFRARED ANDNIGHT-VISIBLE SATELLITE IMAGES. MICROWAVE IMAGERY INDICATES AWELL-DEVELOPED AND CLOSED DEEP-LAYER EYE...ALBEIT TILTED SLIGHTLYTO THE NORTHEAST. A BLEND OF SATELLITE INTENSITY ESTIMATES OFT5.0/90 KT FROM SAB...T4.5/77 KT FROM TAFB...AND UW-CIMSS AVERAGEADT OF T4.7/82 KT IS THE BASIS FOR THE 85-KT ADVISORY INTENSITY.THE INITIAL MOTION ESTIMATE IS 345/08 KT. THERE IS NO SIGNIFICANTCHANGE TO THE PREVIOUS FORECAST TRACK REASONING. OPHELIA ISCURRENTLY ROUNDING THE SOUTHWESTERN PERIPHERY OF A DEEP-LAYERSUBTROPICAL RIDGE SITUATED ALONG 32N LATITUDE. AN UNSEASONABLYSTRONG MID-TROPOSPHERIC TROUGH IS FORECAST TO DEEPEN AND MOVEEASTWARD TO THE U.S. EAST COAST BY 48 HOURS...AND WILL ACT TOACCELERATE AND LIFT OPHELIA NORTHWARD OVER THE NEXT 72 HOURS. BYDAYS 3-4...OPHELIA IS FORECAST TO MERGE WITH A FRONTAL SYSTEM ANDBE OVER MUCH COLDER WATER...WHICH WILL RESULT IN THE CYCLONEBECOMING A STRONG POST-TROPICAL WINTER-TYPE LOW PRESSURE SYSTEMTHAT WILL TURN EASTWARD NEAR THE CANADIAN MARITIMES. THE ONLYNOTICEABLE CHANGE IN THE MODEL GUIDANCE IS A SOUTHWARD SHIFT IN THEGUIDANCE TRACKS AFTER 72 HOURS. IN FACT...THE NEW ECMWF RUN BARELYTAKES OPHELIA AS FAR NORTH AS 45N LATITUDE. THE OFFICIAL FORECASTTRACK WAS NUDGED SLIGHTLY TO THE LEFT THROUGH 72 HOURS...AND THENBROUGHT FARTHER SOUTH IN LINE WITH THE CONSENSUS MODEL...TVCN...BUTNOT AS FAR SOUTH AS THE ECMWF MODEL TRACK.THE OUTFLOW OF OPHELIA REMAINS QUITE IMPRESSIVE...EXCEPT THAT THEWESTERN EDGE OF THE CIRRUS OUTFLOW HAS STARTED TO FLATTEN ANDDISSIPATE AS WESTERLY UPPER-LEVEL WINDS ENCROACH ON THE CYCLONE.HOWEVER...THE LIGHT TO MODERATE WESTERLY VERTICAL WIND SHEAR THATIS CURRENTLY AFFECTING THE CYCLONE IS FORECAST TO TURN MORE FROMSOUTH-SOUTHWEST BY 36-48 HOURS...WHICH SHOULD ALLOW FOR SOMEADDITIONAL STRENGTHENING TO OCCUR. ALTHOUGH FURTHER RAPIDSTRENGTHENING IS A POSSIBILITY...THE VERTICAL SHEAR IS FORECAST BYTHE SHIPS MODEL TO FLUCTUATE BETWEEN 5 AND 15 KT DURING THE NEXT 48HOURS...WHICH SHOULD ACT TO KEEP THE EYE TILTED AT TIMES AND LIKELYDISRUPT THE RAPID INTENSIFICATION PROCESS. AS A RESULT...ONLYMODEST STRENGTHENING IS FORECAST UNTIL OPHELIA REACHES 22C ANDCOLDER SSTS SHORTLY AFTER THE 48-HOUR TIME PERIOD...WHICH IS ALSOCOINCIDENT WITH AN EXPECTED SHARP INCREASE IN THE VERTICAL SHEAR.THE INTENSITY FORECAST IS SIMILAR TO THE INTENSITY CONSENSUSMODEL...ICON...THROUGH 72 HOURS...AND THEN LEANS CLOSE TO THE LGEMMODEL AFTER THAT. IT IS WORTH NOTING THAT SOME OF THE GLOBAL MODELSARE NOW HOLDING ON TO OPHELIA AS A ROBUST EXTRATROPICAL LOWPRESSURE SYSTEM BEYOND 96 HOURS.FORECAST POSITIONS AND MAX WINDSINIT 30/0900Z 22.4N 62.6W 85 KT 100 MPH 12H 30/1800Z 24.2N 63.1W 90 KT 105 MPH 24H 01/0600Z 27.0N 63.4W 90 KT 105 MPH 36H 01/1800Z 30.1N 62.9W 95 KT 110 MPH 48H 02/0600Z 34.6N 61.7W 95 KT 110 MPH 72H 03/0600Z 44.3N 57.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 96H 04/0600Z 51.5N 38.0W 45 KT 50 MPH...POST-TROP/EXTRATROP120H 05/0600Z...DISSIPATED$$FORECASTER STEWART