1100 PM HST WED OCT 22 2014 SATELLITE ANIMATION SHOWS THE LLCC LIKELY LIES JUST BENEATH THE SOUTHERN EDGE OF A SHIELD OF PERSISTENT DEEP CONVECTION. THE OVERALL PRESENTATION IS UNCHANGED FROM LAST TIME...NAMELY THAT OF A WEAK TROPICAL SYSTEM UNDERGOING SOUTHERLY VERTICAL SHEAR. WITH THE EXCEPTION OF A FLANKING LINE OF CB FORMING ALONG A RAIN BAND EAST OF CENTER...PERSISTENT DEEP CONVECTION IS LIMITED TO THE NORTH AND NORTHWEST QUADRANTS. THE LATEST DVORAK-DERIVED INTENSITY FROM ALL THREE SATELLITE FIX CENTERS IS 2.5/35 KT...SO THAT WILL BE THE ASSIGNED INITIAL INTENSITY THIS TIME. THE FORECAST PHILOSOPHY FOR THIS SYSTEM HAS CHANGED LITTLE OVER THE PAST FEW FORECAST CYCLES SINCE ANA BEGAN MOVING FIRMLY TOWARD THE NORTHWEST. INITIAL MOTION IS 325/09 KT...WITH A SLIGHT WOBBLE TO THE LEFT OF PREVIOUS MOTION NOTED WITHIN THE PAST FEW HOURS. ANA WILL CONTINUE MOVING NORTHWEST THROUGH 24 HOURS...THEN NORTHWARD BY 48 HOURS...AS IT IS STEERED ALONG THE SOUTHWEST THEN WEST EDGE OF DEEP HIGH PRESSURE. ANA WILL BEGIN TO INTERACT WITH A DEEP TROUGH APPROACHING FROM THE WEST BY 48 HOURS...CAUSING A TURN TOWARD THE NORTHEAST AND AN INCREASE IN FORWARD SPEED. ANA WILL THEN ACCELERATE TO THE NORTHEAST AS IT UNDERGOES EXTRATROPICAL TRANSITION THROUGH 96 AND 120 HOURS. THE FORECAST TRACK LIES WITHIN A TIGHTLY CLUSTERED GUIDANCE ENVELOPE THROUGH 48 HOURS...THEN BEGINS TO DEVIATE LEFT FROM CONSENSUS AND FAVOR ECMWF AT 72 HOURS AND BEYOND. OUR INTENSITY FORECAST CALLS FOR ANA TO GRADUALLY STRENGTHEN THROUGH 120 HOURS...INITIALLY AS A TROPICAL SYSTEM THROUGH 72 HOURS...THEN AS A TRANSITIONING EXTRATROPICAL LOW AT 96 AND 120 HOURS. INTENSITY GUIDANCE SHOWS WEAKENING VERTICAL SHEAR THROUGH 48 HOURS...AN ENVIRONMENT WHICH WOULD ALLOW ANA TO BENEFIT FROM ANOMALOUSLY WARM OCEAN WATER NEAR AND SOUTH OF 30N. BY 72 HOURS...SEA SURFACE TEMPERATURES WILL BEGIN DECREASING RAPIDLY ALONG THE FORECAST TRACK...CAPPING ANA AT 50 KT THROUGH 96 HOURS. AS THIS SYSTEM CONTINUES MOVING NORTHEASTWARD...DEEP TROUGHING TO THE NORTHWEST WILL BEGIN MERGING WITH IT...BAROCLINICALLY STRENGTHENING ANA...AS A TRANSITIONING EXTRATROPICAL LOW...TO 55 KT. THE OCEAN PREDICTION CENTER CONTRIBUTED TRACK AND INTENSITY GUIDANCE AT 72...96 AND 120 HOURS. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 25.5N 168.4W 35 KT 40 MPH 12H 23/1800Z 26.6N 169.2W 35 KT 40 MPH 24H 24/0600Z 28.3N 169.7W 40 KT 45 MPH 36H 24/1800Z 30.0N 169.4W 45 KT 50 MPH 48H 25/0600Z 31.4N 167.8W 50 KT 60 MPH 72H 26/0600Z 35.8N 161.3W 50 KT 60 MPH 96H 27/0600Z 44.3N 146.9W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 28/0600Z 51.6N 136.5W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ FORECASTER POWELL MC
Posted on: Thu, 23 Oct 2014 08:40:27 +0000
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