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| #221730 (Received by flhurricane at: 4:49 PM 12.Oct.2008) TCDAT4 TROPICAL STORM NANA DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL142008 500 PM EDT SUN OCT 12 2008 ALTHOUGH THE CONVECTIVE ORGANIZATION OF THE AREA OF LOW PRESSURE LOCATED OVER THE EASTERN ATLANTIC HAS DEGRADED SOME THIS AFTERNOON...THE SYSTEM HAS MAINTAINED SUFFICIENT CONVECTION FOR A LONG ENOUGH PERIOD TO CONSIDER IT A TROPICAL CYCLONE. DURING THE AFTERNOON...THE CENTER OF THE CYCLONE HAS BECOME EXPOSED WELL TO THE WEST OF THE LARGE AREA OF DEEP CONVECTION DUE TO WESTERLY SHEAR. AN ASCAT OVERPASS FROM 12Z INDICATED MAXIMUM WINDS OF 30-35 KT. GIVEN THE TYPICAL LOW BIAS OF THIS INSTRUMENT...THE CYCLONE IS DECLARED A TROPICAL STORM...THE FOURTEENTH OF THE 2008 SEASON. THE LONG-TERM SURVIVAL OF NANA SEEMS BLEAK AS STRONG UPPER-LEVEL WESTERLIES ARE FORECAST TO CONTINUE. ALL THE INTENSITY GUIDANCE SHOWS WEAKENING AND SO DOES THE OFFICIAL FORECAST. THE OFFICIAL FORECAST SHOWS NANA DEGENERATING INTO A REMNANT LOW IN ABOUT 48 HOURS...BUT IT WOULD NOT BE SURPRISING IF IT OCCURRED SOONER. NANA HAS BEEN MOVING SLOWLY WEST-NORTHWESTWARD OR 290/6 KT. THE TRACK GUIDANCE PREDICTS A SLOW WEST-NORTHWESTWARD MOTION AROUND THE SOUTH SIDE OF A LOW- TO MID-LEVEL RIDGE OVER THE EASTERN ATLANTIC. THE CYCLONE IS FORECAST TO BE NEAR THE SOUTHWESTERN PERIPHERY OF THE RIDGE IN A COUPLE OF DAYS AND SHOULD TURN TOWARD THE NORTHWEST AHEAD OF A DEEP-LAYER TROUGH THAT DEVELOPS OVER THE CENTRAL ATLANTIC. THE TRACK FORECAST IS CLOSE TO THE MIDDLE OF THE GUIDANCE ENVELOPE...BUT IS SLOWER THAN THE MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INITIAL 12/2100Z 16.4N 37.9W 35 KT 12HR VT 13/0600Z 16.7N 39.0W 30 KT 24HR VT 13/1800Z 17.0N 40.4W 25 KT 36HR VT 14/0600Z 17.4N 41.7W 25 KT 48HR VT 14/1800Z 17.9N 43.0W 25 KT...REMNANT LOW 72HR VT 15/1800Z 19.0N 46.0W 20 KT...REMNANT LOW 96HR VT 16/1800Z...DISSIPATED $$ FORECASTER BROWN |
