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Tropical Storm ALETTA Forecast Discussion Number 10

Issued at 200 PM PDT WED MAY 16 2012

000
WTPZ41 KNHC 162044
TCDEP1
 
TROPICAL STORM ALETTA DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP012012
200 PM PDT WED MAY 16 2012
 
THE CONVECTIVE PATTERN OF THE CYCLONE HAS BECOME DISORGANIZED OVER
THE PAST FEW HOURS...AND NOW CONSISTS OF A SHRINKING BALL OF DEEP
CONVECTION NEAR THE CENTER AND A DISCONNECTED BAND TO THE EAST.
THE LOW-LEVEL CENTER IS PARTIALLY EXPOSED ON THE SOUTHWESTERN EDGE
OF THE MAIN CONVECTIVE MASS...INDICATIVE THAT SOUTHWESTERLY SHEAR
MAY FINALLY BE TAKING A TOLL ON THE CYCLONE.  ALTHOUGH DVORAK
T-NUMBERS REMAIN AT 2.5 AT 1800 UTC...IT APPEARS AS IF A WEAKENING
TREND MAY HAVE ALREADY BEGUN.  THE INITIAL INTENSITY IS HELD AT 35
KT FOR THIS ADVISORY...ASSUMING THAT THE CYCLONE HAS WEAKENED A BIT
SINCE A 1643 UTC ASCAT PASS SHOWED A COUPLE OF 40-KT VECTORS.  THE
GLOBAL MODELS SHOW MODERATE TO STRONG SOUTHWESTERLY SHEAR
PERSISTING OVER THE NEXT SEVERAL DAYS...AS ALETTA MOVES INTO A
REGION DOMINATED BY AN INCREASINGLY STABLE AND DRIER AIR MASS. 
THESE TWO SIGNIFICANT NEGATIVE FACTORS SHOULD HASTEN THE DEMISE OF
THE CYCLONE...AND THE OFFICIAL NHC FORECAST NOW CALLS FOR ALETTA TO
DEGENERATE INTO A REMNANT LOW IN ABOUT 48 HOURS.
 
CENTER FIXES FROM SEVERAL MICROWAVE PASSES THIS MORNING AND RECENT
VISIBLE SATELLITE IMAGES INDICATE THAT ALETTA HAS BEEN MAINTAINING
A MORE WESTERLY MOTION...270/08...THAN INDICATED IN PREVIOUS
ADVISORIES.  UNDER THE EASTERN PERIPHERY OF A MID-LEVEL RIDGE...
ALETTA SHOULD CONTINUE ON A GENERALLY WESTWARD TRACK FOR THE NEXT
12 HOURS OR SO.  THEREAFTER...THE LARGE-SCALE MODELS SHOW THE RIDGE
NORTH OF THE STORM ERODING AS A WEAKNESS DEVELOPS SOUTH OF BAJA
CALIFORNIA.  THIS SHOULD CAUSE THE TRACK OF THE STORM TO TURN
NORTHWARD WITHIN 36 HOURS WITH A DECREASE IN FORWARD SPEED. 
THEREAFTER...THE REMNANT CIRCULATION IS EXPECTED TO TURN TOWARD THE
NORTHEAST AND THEN TOWARD THE EAST AS IT BECOME EMBEDDED IN
ANOMALOUS LOW-LEVEL WESTERLY FLOW SOUTH OF MAINLAND MEXICO.  THE
OFFICIAL TRACK FORECAST IS CLOSE TO THE PREVIOUS ONE THROUGH 36
HOURS AND A BIT MORE EASTWARD/FASTER AT LATER FORECAST TIMES...IN
LINE WITH THE LATEST GUIDANCE.
 
THE WIND RADII WERE ADJUSTED INWARD BASED UPON THE EARLIER ASCAT
PASS. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  16/2100Z 11.4N 113.5W   35 KT  40 MPH
 12H  17/0600Z 11.7N 114.4W   30 KT  35 MPH
 24H  17/1800Z 12.4N 115.1W   30 KT  35 MPH
 36H  18/0600Z 13.1N 115.0W   25 KT  30 MPH
 48H  18/1800Z 13.6N 114.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  19/1800Z 14.0N 113.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  20/1800Z 14.0N 111.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  21/1800Z...DISSIPATED
 
$$
FORECASTER KIMBERLAIN
 

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