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Tropical Storm COSME Forecast Discussion Number 4
2013-06-24 10:45:06| National Hurricane Center (East Pacific)
Issued at 200 AM PDT MON JUN 24 2013 000 WTPZ43 KNHC 240844 TCDEP3 TROPICAL STORM COSME DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP032013 200 AM PDT MON JUN 24 2013 DURING THE PAST 6 HOURS...CONVECTION HAS INCREASED SOMEWHAT NEAR THE CENTER OF THE TROPICAL CYCLONE...AND SEVERAL SATELLITE INTENSITY ESTIMATES INDICATE THAT THE SYSTEM HAS STRENGTHENED INTO TROPICAL STORM COSME. IN FACT...ASCAT-B AND ASCAT-A SCATTEROMETER PASSES AT 0404Z AND 0450Z...RESPECTIVELY...INDICATED SEVERAL 34- TO 37-KT WIND VECTORS IN THE SOUTHEASTERN QUADRANT. THE ASCAT DATA ALSO REVEALED THAT COSME HAD MOVED MORE WESTWARD SINCE THE PREVIOUS ADVISORY...AND THAT THE CENTER AS LOCATED ON THE NORTHERN EDGE OF A SMALL CDO-LIKE CONVECTIVE FEATURE. THE INITIAL MOTION ESTIMATE IS 305/09 KT. NORTHERLY TO NORTHEASTERLY MID-LEVEL SHEAR OF 10-15 KT AS INDICATED IN UW-CIMMS SHEAR ANALYSES IS THE LIKELY REASON FOR THE RECENT WESTWARD MOTION. HOWEVER... THIS IS EXPECTED TO BE A TEMPORARY MOTION AND COSME IS FORECAST TO BEGIN TO TURN BACK TOWARD THE NORTHWEST LATER THIS MORNING AS THE CYCLONE GRADUALLY MOVES OUT OF THE NORTHERLY MID-LEVEL SHEAR ENVIRONMENT. AFTERWARDS...A DEEP-LAYER RIDGE TO THE NORTH OF COSME SHOULD GRADUALLY TURN THE CYCLONE TOWARD THE WEST-NORTHWEST BY 48 HOURS. NEAR THE END OF THE FORECAST PERIOD...THE EXPECTED WEAKENING AND VERTICALLY SHALLOW CYCLONE SHOULD BE STEERED WESTWARD WITHIN THE LOW-LEVEL EASTERLY TRADE WIND FLOW. SINCE COSME IS ALREADY AT LEAST 30 NMI TO THE LEFT OF THE PREVIOUS FORECAST TRACK...THE NEW ADVISORY TRACK HAS BEEN SHIFTED SLIGHTLY TO THE WEST AND SOUTH... AND BASICALLY LIES ALONG THE EXTREME SOUTHERN EDGE OF TIGHTLY PACKED MODEL GUIDANCE ENVELOPE. THE AFOREMENTIONED MID-LEVEL SHEAR THAT HAS BEEN UNDERCUTTING THE OTHERWISE VERY FAVORABLE UPPER-LEVEL OUTFLOW PATTERN HAS BEEN HINDERING THE DEVELOPMENT OF PERSISTENT DEEP CONVECTION NEAR THE CENTER. HOWEVER...AS COSME CONTINUES TO MOVE NORTHWESTWARD...THE CYCLONE WILL ENTER A LESS HOSTILE SHEAR ENVIRONMENT...WHICH WILL ALLOW FOR MORE SIGNIFICANT STRENGTHENING TO OCCUR UNTIL THE SYSTEM REACHES MUCH COOLER WATERS BY 72 HOURS. DESPITE VERY FAVORABLE ATMOSPHERIC AND OCEANIC CONDITIONS FOR THE NEXT 2-3 DAYS...THE LARGE RADIUS OF MAXIMUM WINDS OF AT LEAST 90 NMI SHOULD KEEP INTENSIFICATION SLOWER THAN THE AVERAGE RATE OF ONE T-NUMBER PER DAY. BY 72 HOURS...COSME WILL BE MOVING OVER COOLER WATERS AND RAPID WEAKENING IS EXPECTED TO ENSUE. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY...AND IS SIMILAR TO A BLEND OF THE SHIPS AND SHIFOR INTENSITY MODELS. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 12.8N 105.2W 35 KT 40 MPH 12H 24/1800Z 13.9N 106.5W 40 KT 45 MPH 24H 25/0600Z 15.2N 108.5W 45 KT 50 MPH 36H 25/1800Z 16.2N 110.8W 55 KT 65 MPH 48H 26/0600Z 17.0N 113.3W 65 KT 75 MPH 72H 27/0600Z 18.5N 118.3W 50 KT 60 MPH 96H 28/0600Z 19.7N 124.0W 35 KT 40 MPH 120H 29/0600Z 20.0N 129.2W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER STEWART
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