000
WTPZ41 KNHC 161434
TCDEP1
 
TROPICAL STORM ALETTA DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP012012
800 AM PDT WED MAY 16 2012
 
THE OVERALL CLOUD PATTERN OF ALETTA DOES NOT APPEAR SIGNIFICANTLY
DIFFERENT IN SATELLITE IMAGERY THIS MORNING...EXCEPT FOR SOME NEW
CONVECTIVE GROWTH NEAR THE ESTIMATED CENTER. INTERESTINGLY...THE
CONVECTIVE ORGANIZATION OF THE TROPICAL CYCLONE IS NOT SUGGESTIVE
OF MODERATE SOUTHWESTERLY SHEAR...AS CURRENTLY DIAGNOSED BY THE
SHIPS MODEL AND UW-CIMSS ANALYSES. SATELLITE CLASSIFICATIONS ARE THE
SAME AS EARLIER...SO THE INITIAL INTENSITY IS HELD AT 35 KT. THE
ENVIRONMENT AHEAD OF ALETTA IS EXPECTED TO BECOME INCREASINGLY
UNFAVORABLE DURING THE NEXT COUPLE OF DAYS...AS THE CYCLONE IS
FORECAST TO INGEST A MUCH DRIER...STABLE AIR MASS AND BE AFFECTED
BY PERSISTENT MODERATE TO STRONG WESTERLY SHEAR. THESE NEGATIVE
FACTORS SHOULD RESULT IN A STEADY OR PERHAPS EVEN RAPID WEAKENING
OF THE CYCLONE...AND THE OFFICIAL FORECAST NOW INDICATES THAT
ALETTA WILL DEGENERATE INTO A REMNANT LOW IN 2 TO 3 DAYS.
 
THE CENTER OF ALETTA WAS DIFFICULT TO LOCATE OVERNIGHT...BUT A 1145
UTC TRMM PASS SUGGESTS THAT THE CYCLONE IS LOCATED FARTHER SOUTH
THAN PREVIOUS ESTIMATES. THE INITIAL MOTION ESTIMATE IS 280/08...AND
THERE HAS BEEN NO CHANGE TO THE TRACK FORECAST REASONING. ALETTA IS
EXPECTED TO CONTINUE WESTWARD TO WEST-NORTHWESTWARD FOR ANOTHER 12
HOURS OR SO UNDER THE INFLUENCE OF A MID-LEVEL RIDGE TO THE NORTH.
AFTER THAT TIME...THE COMBINATION OF A DEVELOPING WEAKNESS
NORTHWEST OF THE CYCLONE AND ANOMALOUS LOW-LEVEL WESTERLY FLOW SOUTH
OF MAINLAND MEXICO SHOULD CAUSE ALETTA TO TURN NORTHWARD AND THEN
NORTHEASTWARD OR EVEN EASTWARD AS IT WEAKENS AND BECOMES A SHALLOW
CYCLONE. THE OFFICIAL NHC TRACK FORECAST IS ESSENTIALLY AN UPDATE OF
THE PREVIOUS ONE THROUGH ABOUT 48 HOURS...AND IS ADJUSTED TO THE
RIGHT AFTER THAT IN RESPONSE TO AN EASTWARD SHIFT IN THE GUIDANCE
AT THOSE TIMES.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  16/1500Z 11.8N 112.6W   35 KT  40 MPH
 12H  17/0000Z 12.1N 113.8W   35 KT  40 MPH
 24H  17/1200Z 12.6N 114.7W   30 KT  35 MPH
 36H  18/0000Z 13.0N 115.2W   25 KT  30 MPH
 48H  18/1200Z 13.5N 115.3W   25 KT  30 MPH
 72H  19/1200Z 14.1N 114.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  20/1200Z 14.5N 113.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  21/1200Z...DISSIPATED
 
$$
FORECASTER KIMBERLAIN