000 WTPZ41 KNHC 170241 TCDEP1 TROPICAL STORM ALVIN DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012013 800 PM PDT THU MAY 16 2013 ALVIN CONTINUES TO PRODUCE DISORGANIZED DEEP CONVECTION IN BROKEN BANDS TO THE SOUTHEAST AND WEST OF THE CENTER. THE CENTER OF CIRCULATION REMAINS EMBEDDED IN THE ITCZ AND COULD BE IN THE PROCESS OF DEGENERATING INTO AN OPEN TROUGH. SATELLITE INTENSITY ESTIMATES ARE 1.5 AND 2.5 FROM SAB AND TAFB...RESPECTIVELY. DESPITE THE RAGGED APPEARANCE OF THE CYCLONE IN SATELLITE IMAGERY...THE INITIAL INTENSITY ESTIMATE IS CONSERVATIVELY REDUCED TO 35 KT UNTIL THERE IS MORE DEFINITIVE PROOF THAT ADDITIONAL WEAKENING HAS OCCURRED. ALVIN IS LOCATED ON THE SOUTHERN EDGE OF A BELT OF STRONG WESTERLY FLOW ASSOCIATED WITH AN UPPER-LEVEL TROUGH LOCATED SEVERAL HUNDRED MILES WEST OF THE BAJA CALIFORNIA PENINSULA. AS A RESULT...UW-CIMSS SHEAR ANALYSES CONTINUE TO DIAGNOSE 20-25 KT OF WEST-SOUTHWESTERLY SHEAR OVER THE CYCLONE. IT IS UNLIKELY THAT THE SHEAR WILL DECREASE DURING THE FORECAST PERIOD...ACCORDING TO THE ECMWF/UKMET MODELS WHICH HAVE MORE ACCURATELY FORECAST THE UPPER-AIR PATTERN NEAR ALVIN THAN HAS THE GFS. IT IS THEREFORE DIFFICULT TO IMAGINE ALVIN STAGING A COMEBACK IN WHAT IS FORECAST TO BE AN INCREASINGLY HOSTILE ENVIRONMENT OVER THE NEXT FEW DAYS. THE NEW NHC INTENSITY FORECAST IS SIMILAR TO OR SLIGHTLY LOWER THAN THE PREVIOUS ONE AND A BIT LOWER THAN THE LATEST INTENSITY GUIDANCE. ALVIN IS EXPECTED TO DEGENERATE INTO A REMNANT LOW OR AN OPEN TROUGH IN THREE DAYS...IF NOT SOONER. THE INITIAL MOTION ESTIMATE IS 285/12. ALVIN SHOULD CONTINUE MOVING WEST-NORTHWESTWARD FOR THE NEXT DAY OR TWO AROUND THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL RIDGE CENTERED OVER SOUTHERN MEXICO. THE GLOBAL MODELS THEN SHOW THE MID-LEVEL CENTER OF ALVIN BEING CARRIED NORTHWESTWARD AND NORTHWARD AHEAD OF A LARGE UPPER-LEVEL TROUGH NEAR 120W...WITH THE LOW-LEVEL REMNANT VORTICITY CENTER LIKELY SEPARATING FROM IT AND MOVING ON A MORE WESTERLY COURSE IN THE TRADE WIND FLOW. THE TRACK GUIDANCE AGREES WELL ON THIS SCENARIO... AND THE NHC TRACK FORECAST IS NEAR OR JUST LEFT OF THE PREVIOUS ONE AND THE MULTI-MODEL CONSENSUS TVCE. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 9.8N 110.8W 35 KT 40 MPH 12H 17/1200Z 10.2N 111.8W 35 KT 40 MPH 24H 18/0000Z 11.0N 113.2W 35 KT 40 MPH 36H 18/1200Z 11.7N 114.5W 30 KT 35 MPH 48H 19/0000Z 12.1N 115.9W 30 KT 35 MPH 72H 20/0000Z 12.5N 119.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 21/0000Z 12.3N 121.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 22/0000Z 12.0N 123.5W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ FORECASTER KIMBERLAIN