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Tropical Storm LORENZO Forecast Discussion Number 7
2013-10-23 04:39:48| National Hurricane Center (Atlantic)
Issued at 1100 PM AST TUE OCT 22 2013 000 WTNT43 KNHC 230239 TCDAT3 TROPICAL STORM LORENZO DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132013 1100 PM AST TUE OCT 22 2013 SHEAR ANALYSES FROM THE UNIVERSITY OF WISCONSIN INDICATE THAT DEEP-LAYER SHEAR NEAR LORENZO HAS TURNED OUT OF THE NORTHWEST AND INCREASED TO NEARLY 25 KT. AS A CONSEQUENCE...MOST OF THE DEEP CONVECTION HAS BEEN PUSHED TO THE SOUTHEAST OF THE LOW-LEVEL CENTER. THERE HAVE BEEN NO ASCAT PASSES OVER LORENZO SINCE THIS TIME YESTERDAY...SO THE INITIAL INTENSITY IS KEPT AT 45 KT BASED ON ESTIMATES FROM INFRARED SATELLITE IMAGERY. VERTICAL SHEAR IS EXPECTED TO INCREASE EVEN FURTHER TO AROUND 40 KT OUT OF THE NORTH WITHIN 24 HOURS...AND WEAKENING IS THEREFORE FORECAST TO BEGIN VERY SOON. THE COMBINED INFLUENCE OF VERY STRONG SHEAR AND COOLER WATERS SHOULD CAUSE LORENZO TO DEGENERATE TO A REMNANT LOW IN 48 HOURS. THE UPDATED NHC INTENSITY FORECAST IS CLOSE TO THE INTENSITY CONSENSUS AND UNCHANGED FROM THE PREVIOUS FORECAST...AND IT STILL SHOWS DISSIPATION IN 3 DAYS. LORENZO IS LOCATED JUST TO THE NORTH OF A MID-LEVEL RIDGE AND JUST TO THE SOUTH OF FAST MID-LATITUDE WESTERLIES...WHICH ARE STEERING THE CYCLONE EASTWARD AT 085/8 KT. WEAKER LOW-LEVEL FLOW SHOULD EXERT A GREATER INFLUENCE ON STEERING AS THE CYCLONE BECOMES MORE SHALLOW...AND LORENZO IS EXPECTED TO TURN SLOWLY NORTHEASTWARD OVER THE NEXT 36 HOURS AHEAD OF AN APPROACHING COLD FRONT. THERE ARE SOME SPEED DIFFERENCES AMONG THE TRACK GUIDANCE...WITH THE GFS AND ECMWF MODELS SHOWING A FASTER MOTION COMPARED TO THE GFDL AND HWRF MODELS. THE OFFICIAL TRACK FORECAST HEDGES TOWARD THE GLOBAL MODEL SCENARIOS AND IS THEREFORE A LITTLE FASTER THAN THE MULTI-MODEL CONSENSUS TVCA...ESPECIALLY AT 36 AND 48 HOURS. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 29.6N 50.0W 45 KT 50 MPH 12H 23/1200Z 29.8N 49.2W 40 KT 45 MPH 24H 24/0000Z 30.3N 48.4W 35 KT 40 MPH 36H 24/1200Z 31.4N 47.3W 30 KT 35 MPH 48H 25/0000Z 32.6N 45.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 26/0000Z...DISSIPATED $$ FORECASTER BERG
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