Tropical Storm NATE

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TROPICAL STORM NATE DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL152011
1000 PM CDT WED SEP 07 2011

SATELLITE IMAGERY...CONVENTIONAL AND MICROWAVE...SHOWS LITTLE CHANGE
IN EITHER THE POSITION OR THE ORGANIZATION OF NATE DURING THE PAST
SEVERAL HOURS.  THE LOW-LEVEL CENTER REMAINS EXPOSED ABOUT 60 N MI
NORTHEAST OF THE MAIN CONVECTIVE AREA...AND OVERALL THE SYSTEM
RETAINS A SOMEWHAT BAROCLINIC APPEARANCE DUE TO ITS POSITION NEAR
THE SOUTHWESTERN END OF A FRONTAL ZONE.  SATELLITE INTENSITY
ESTIMATES FROM TAFB AND SAB ARE BELOW TROPICAL STORM STRENGTH. 
HOWEVER...A SHIP REPORTED 40 KT WINDS SOUTHEAST OF THE CENTER AT
0000 UTC....AND THAT IS THE BASIS FOR THE INITIAL INTENSITY.

THE INITIAL MOTION IS A VERY UNCERTAIN 090/2...AND IT IS LIKELY THAT
FOR THE NEXT DAY OR SO REFORMATIONS OF THE CENTER WILL CAUSE LARGER
CHANGES IN POSITION THAN THE ACTUAL MOTION OF THE CYCLONE. AFTER
THAT TIME...RISING PRESSURES TO THE NORTH AND NORTHEAST SHOULD
CAUSE NATE TO BEGIN A SLOW NORTHWESTWARD MOTION...WHICH MOST OF THE
GUIDANCE SHOWS NATE TURNING WESTWARD BY 120 HOURS. THERE REMAINS A
LOT OF NORTH-TO-SOUTH SPREAD IN THE TRACK GUIDANCE...AND THE
CANADIAN MODEL IS A MAJOR OUTLIER IN SHOWING A MOTION TOWARD THE
NORTHERN GULF COAST. THAT SOLUTION IS DISCOUNTED FOR THIS FORECAST.
THE FORECAST TRACK IS SIMILAR TO THE PREVIOUS ONE AND SHOWS THE
CENTER OF NATE REMAINING OVER THE BAY OF CAMPECHE FOR THE NEXT FIVE
DAYS.

NATE IS FORECAST TO REMAIN IN AN AREA OF LIGHT VERTICAL WIND SHEAR
FOR THE NEXT 36-48 HOURS...AND THE INTENSITY GUIDANCE RESPONDS TO
THIS LOW SHEAR AND THE WARM UNDERLYING WATERS BY FORECASTING
STRENGTHENING.  HOWEVER...THERE IS ABUNDANT DRY AIR TO THE
NORTHWEST OF NATE WHICH COULD SLOW THE RATE OF STRENGTHENING IF THE
STORM INGESTS IT...AND THE CURRENT STORM STRUCTURE IS NOT FAVORABLE
FOR RAPID STRENGTHENING.  BASED ON THIS...THE INTENSITY FORECAST
SHOWS GRADUAL STRENGTHENING INTO A HURRICANE DURING THAT TIME. 
AFTER 48 HOURS...THE GLOBAL MODELS ARE DIVIDED ON HOW MUCH WIND
SHEAR NATE MIGHT ENCOUNTER...WITH THE ECMWF FORECASTING A MORE
FAVORABLE ENVIRONMENT THAN THE OTHER MODELS.  DUE TO THE
UNCERTAINTY...THE NEW INTENSITY FORECAST IS UNCHANGED FROM THE
PREVIOUS ADVISORY.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  08/0300Z 20.4N  92.5W   40 KT  45 MPH
 12H  08/1200Z 20.3N  92.2W   45 KT  50 MPH
 24H  09/0000Z 20.5N  92.0W   50 KT  60 MPH
 36H  09/1200Z 21.1N  92.2W   55 KT  65 MPH
 48H  10/0000Z 21.7N  92.8W   65 KT  75 MPH
 72H  11/0000Z 23.0N  94.0W   70 KT  80 MPH
 96H  12/0000Z 23.5N  95.5W   75 KT  85 MPH
120H  13/0000Z 23.5N  97.0W   75 KT  85 MPH
 
$$
FORECASTER BEVEN
 
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