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| #378385 (Received by flhurricane at: 4:56 AM 24.Sep.2010) TCDAT5 TROPICAL STORM MATTHEW DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL152010 500 AM EDT FRI SEP 24 2010 MATTHEW HAS GOTTEN SLIGHTLY BETTER ORGANIZED OVER THE PAST SEVERAL HOURS. WHILE THE STORM HAS A LARGE CONVECTIVE CLUSTER WITH CLOUD TOPS COLDER THAN -80C...THE LOW-LEVEL CENTER IS NEAR THE EASTERN EDGE OF THE CONVECTION. THIS IS LIKELY DUE TO 15 KT OF EAST- NORTHEASTERLY VERTICAL WIND SHEAR SHOWN IN ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN. IN ADDITION...EARLIER MICROWAVE DATA SUGGESTS THAT THERE ARE MULTIPLE LOW-LEVEL SWIRLS PRESENT. SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM TAFB AND 35 KT FROM SAB...AND BASED ON THESE THE INITIAL INTENSITY IS INCREASED TO 45 KT. THE INITIAL MOTION IS 275/14. MATTHEW IS ON THE SOUTH SIDE OF THE SUBTROPICAL RIDGE...WHICH IS EXPECTED TO STEER THE CYCLONE WESTWARD TO WEST-NORTHWESTWARD WITH SOME DECREASE IN FORWARD SPEED FOR THE NEXT 36-48 HR. THE GUIDANCE IS IN GOOD AGREEMENT WITH THIS...AND THE NEW FORECAST TRACK LIES A LITTLE TO THE NORTH OF THE CENTER OF THE GUIDANCE ENVELOPE. AFTER THAT TIME...THERE IS SERIOUS DIVERGENCE IN THE GUIDANCE. THE OPERATIONAL GLOBAL MODELS AGREE THAT MATTHEW SHOULD CONTINUE WEST-NORTHWESTWARD ACROSS THE SOUTHERN YUCATAN PENINSULA AND/OR GUATEMALA...WITH THE UKMET SHOWING THE CENTER REACHING THE BAY OF CAMPECHE. ON THE OTHER HAND...THE GFDL..HWRF...AND GFS ENSEMBLE MEAN FORECAST MATTHEW TO REACH THE EAST COAST OF YUCATAN AND THEN TURN NORTHEASTWARD. THE DIFFERENCES APPEAR TO STEM FROM THE INTERACTION OF MATTHEW WITH A DEVELOPING MONSOON LOW PRESSURE AREA OVER CENTRAL AMERICA AND THE ADJACENT WATERS...AND TO A LESSER EXTENT ON THE DEVELOPMENT OF A DEEP-LAYER TROUGH OVER THE CENTRAL AND EASTERN UNITED STATES. FOR NOW...THE TRACK FORECAST WILL COMPROMISE BETWEEN THESE EXTREMES AND CALL FOR A SLOW NORTHWARD MOTION OVER THE YUCATAN PENINSULA TO KEEP CONTINUITY FROM THE PREVIOUS FORECAST. HOWEVER...THIS IS A LOW-CONFIDENCE FORECAST...AND SIGNIFICANT CHANGES MAY BE REQUIRED LATER TODAY. THE CURRENT SHEAR IS FORECAST TO SUBSIDE IN 12-24 HR...SO THE MAIN FACTOR CONTROLLING THE INTENSITY WILL BE LAND INTERACTION. THE NEW FORECAST TRACK HAS MATTHEW PASSING OVER MORE LAND THAN PREVIOUSLY AND THE FORECAST INTENSITIES HAVE THUS BEEN LOWERED. IT SHOULD BE NOTED THAT NONE OF THE INTENSITY GUIDANCE SHOWS MATTHEW BECOMING A HURRICANE BEFORE REACHING HONDURAS AND NICARAGUA...BUT THIS POSSIBILITY CANNOT BE RULED OUT. THE INTENSITY OF MATTHEW AFTER 48 HR IS HIGHLY DEPENDENT ON WHICH GROUPS OF MODELS ARE CORRECT ABOUT THE TRACK. IF THE GLOBAL MODELS VERIFY...THE CYCLONE WILL LIKELY DISSIPATE OVER EASTERN MEXICO OR GUATEMALA. IF THE GFDL/HWRF VERIFY...THE SYSTEM WILL BE STRONGER THAN FORECAST OVER THE CARIBBEAN WATERS. THE LATTER PART OF THE INTENSITY FORECAST IS A COMPROMISE BETWEEN THESE EXTREMES...AND LIKE THE TRACK FORECAST...IT IS OF LOW CONFIDENCE. FORECAST POSITIONS AND MAX WINDS INITIAL 24/0900Z 14.3N 79.8W 45 KT 12HR VT 24/1800Z 14.8N 82.0W 50 KT 24HR VT 25/0600Z 15.5N 84.5W 50 KT...INLAND 36HR VT 25/1800Z 16.2N 86.5W 50 KT...OVER WATER 48HR VT 26/0600Z 16.7N 87.9W 60 KT 72HR VT 27/0600Z 17.5N 89.5W 35 KT...INLAND 96HR VT 28/0600Z 18.5N 89.5W 30 KT...INLAND 120HR VT 29/0600Z 19.5N 89.5W 25 KT...INLAND $$ FORECASTER BEVEN |
