000
WTNT44 KNHC 122047
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