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Tropical Depression THIRTEEN-E Forecast Discussion Number 2

Issued at 700 PM PST SAT NOV 19 2011

000
WTPZ43 KNHC 200237
TCDEP3
 
TROPICAL DEPRESSION THIRTEEN-E DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP132011
700 PM PST SAT NOV 19 2011

SATELLITE IMAGERY THIS EVENING SHOWS THAT THE SHOWER ACTIVITY
ASSOCIATED WITH THE DEPRESSION IS GRADUALLY BECOMING BETTER
ORGANIZED...WITH A SMALL CONVECTIVE AREA NEAR THE CENTER AND AN
OUTER BAND IN THE EASTERN SEMICIRCLE.  SATELLITE INTENSITY
ESTIMATES ARE 30 KT FROM SAB AND TAFB...AND THAT REMAINS THE
INITIAL INTENSITY.  THE CYCLONE CURRENTLY HAS GOOD CIRRUS OUTFLOW
IN ALL DIRECTIONS EXCEPT TO THE SOUTHEAST.

THE INITIAL MOTION IS 280-285 DEGREES AT ABOUT 10 KT.  THE
DEPRESSION REMAINS ON THE SOUTH SIDE OF A MID/UPPER-LEVEL RIDGE
EXTENDING FROM THE SOUTHERN GULF OF MEXICO WEST-SOUTHWESTWARD
ACROSS MEXICO.  THIS RIDGE IS CURRENTLY WEAKENING SLIGHTLY AS A
LARGE DEEP-LAYER TROUGH MOVES SOUTHEASTWARD INTO CALIFORNIA.  THE
DYNAMICAL MODELS FORECAST THIS TROUGH TO PASS NORTH OF THE
DEPRESSION DURING THE NEXT 24-48 HOURS...WITH THE RIDGE BUILDING
WESTWARD AS THE TROUGH MOVES AWAY.  THIS EVOLUTION IS EXPECTED TO
ALLOW THE DEPRESSION TO MOVE GENERALLY WEST-NORTHWESTWARD FOR 24-36
HOURS...WITH A WESTWARD TURN AFTER THAT AS THE RIDGE REBUILDS. 
TOWARD THE END OF THE FORECAST PERIOD...A SECOND TROUGH OVER THE
NORTHEASTERN PACIFIC SHOULD AGAIN WEAKEN THE RIDGE AND ALLOW A
WEST-NORTHWESTWARD MOTION TO OCCUR.  THE TRACK FORECAST GUIDANCE IS
IN GOOD AGREEMENT WITH THIS SCENARIO...ALTHOUGH THE ECMWF MODEL
SHOWS A MORE WESTWARD MOTION THAN THE OTHER MODELS LATE IN THE
FORECAST PERIOD.  THE NEW TRACK FORECAST IS CLOSE TO THE PREVIOUS
TRACK AND NEAR THE CENTER OF THE GUIDANCE ENVELOPE.

THE DEPRESSION IS EMBEDDED IN AN ENVIRONMENT OF LIGHT VERTICAL WIND
SHEAR...AND ALL GUIDANCE FORECASTS THIS TO CONTINUE FOR THE NEXT
FIVE DAYS.  THUS...SEA SURFACE TEMPERATURES AND ATMOSPHERIC
THERMODYNAMICS WILL BE THE MAIN FACTORS CONTROLLING THE INTENSITY. 
THE FIRST PART OF THE FORECAST TRACK TAKES THE CYCLONE OVER
INCREASING SEA SURFACE TEMPERATURES...AND IN RESPONSE THE
SHIPS...GFDL...AND HWRF MODELS FORECAST THE SYSTEM TO BECOME A
HURRICANE IN 48-60 HOURS.  HOWEVER...THE LGEM MODEL CALLS FOR A
PEAK INTENSITY UNDER HURRICANE STRENGTH.  THE NEW INTENSITY
FORECAST CALLS FOR MORE STRENGTHENING THAN THE PREVIOUS FORECAST...
ALTHOUGH IT IS NOT AS AGGRESSIVE AS THE SHIPS...GFDL...OR HWRF. 
THE CYCLONE SHOULD ENCOUNTER DECREASING SEA SURFACE TEMPERATURES BY
120 HOURS...AND THIS IS REFLECTED IN THE FORECAST WEAKENING AT THAT
TIME.

IF THE DEPRESSION BECOMES A TROPICAL STORM...IT WOULD BE THE
LATEST-FORMING NAMED STORM IN THE EASTERN PACIFIC SINCE HURRICANE
WINNIE IN 1983...WHICH FORMED ON DECEMBER 4.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  20/0300Z 10.3N 102.1W   30 KT  35 MPH
 12H  20/1200Z 10.7N 103.4W   35 KT  40 MPH
 24H  21/0000Z 11.3N 105.5W   40 KT  45 MPH
 36H  21/1200Z 11.7N 108.0W   50 KT  60 MPH
 48H  22/0000Z 11.9N 110.4W   55 KT  65 MPH
 72H  23/0000Z 12.0N 114.5W   65 KT  75 MPH
 96H  24/0000Z 12.5N 119.0W   70 KT  80 MPH
120H  25/0000Z 13.5N 123.0W   55 KT  65 MPH
 
$$
FORECASTER BEVEN
 

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