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Tropical Storm ALETTA Forecast Discussion Number 6

Issued at 200 PM PDT TUE MAY 15 2012

000
WTPZ41 KNHC 152035
TCDEP1
 
TROPICAL STORM ALETTA DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP012012
200 PM PDT TUE MAY 15 2012
 
THE OVERALL ORGANIZATION OF THE CYCLONE IMPROVED AROUND THE TIME OF
THE ISSUANCE OF THE PREVIOUS ADVISORY.  A 1528 UTC SSMIS MICROWAVE
IMAGE SHOWED A BAND OF CONVECTION THAT WRAPPED AROUND THE NORTHEAST
AND EAST SIDE OF THE CIRCULATION.  VERY RECENTLY...A NEW BURST OF
DEEP CONVECTION HAS FORMED NEAR THE ESTIMATED CENTER.  OBJECTIVE
AND SUBJECTIVE DVORAK T-NUMBERS BETWEEN 2.5 AND 3.0 YIELD AN
INITIAL INTENSITY OF 40 KT.  ENVIRONMENTAL CONDITIONS APPEAR
MARGINALLY CONDUCIVE FOR SOME MODEST STRENGTHENING DURING THE NEXT
12 HOUR OR SO.  AFTER THAT...MODERATE SOUTHWESTERLY SHEAR AND SOME
DRIER AIR ARE EXPECTED TO NEGATIVELY IMPACT THE CYCLONE.  THE GFS
AND SHIPS OUTPUT SUGGEST A LITTLE LESS SHEAR THAN THE ECMWF AND
UKMET MODELS WHICH SHOW STRONGER UPPER-LEVEL WESTERLY FLOW
IMPINGING ON THE CYCLONE.  IN DEFERENCE TO THE LATTER TWO
MODELS...THE OFFICIAL FORECAST CALLS FOR A LITTLE FASTER RATE OF
WEAKENING THAN THE SHIPS/LGEM GUIDANCE.
 
ALETTA CONTINUES TO MOVE WESTWARD TO THE SOUTH OF A MID-LEVEL RIDGE
THAT IS LOCATED WEST OF BAJA CALIFORNIA. IN A COUPLE OF DAYS...THE
RIDGE IS FORECAST TO WEAKEN...AND THIS IS EXPECTED TO CAUSE THE
CYCLONE TO SLOW DOWN.  THERE IS NOW CONSIDERABLE SPREAD IN THE
TRACK GUIDANCE AFTER 36 HOURS.  THE ECMWF TURNS ALETTA NORTHWARD
AND THEN EASTWARD AS THE CYCLONE BECOMES EMBEDDED IN SOUTHWESTERLY
LOW-LEVEL FLOW.  THE GFS AND UKMET SHOW ALETTA MOVING FARTHER
WESTWARD BEFORE DECELERATING AND TURNING NORTHWARD.  HOWEVER...THE
OVERALL TRENDS OF THESE MODELS IS TOWARD THE EAST.  BECAUSE OF
THIS...THE OFFICIAL FORECAST IS ONCE AGAIN SLOWED DOWN AND SHIFTED
EASTWARD AND IS IN BEST AGREEMENT WITH THE GFS/UKMET MODELS.  THE
NHC FORECAST LIES SIGNIFICANTLY WEST OF THE ECMWF MODEL AND THE
MULTI-MODEL CONSENSUS AND ADDITIONAL EASTWARD SHIFTS MAY BE
REQUIRED IF THE CURRENT MODEL TRENDS CONTINUE.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  15/2100Z 11.2N 110.4W   40 KT  45 MPH
 12H  16/0600Z 11.4N 111.8W   45 KT  50 MPH
 24H  16/1800Z 11.8N 113.8W   40 KT  45 MPH
 36H  17/0600Z 11.9N 115.5W   35 KT  40 MPH
 48H  17/1800Z 12.3N 116.8W   30 KT  35 MPH
 72H  18/1800Z 12.8N 118.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  19/1800Z 13.5N 118.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  20/1800Z...DISSIPATED
 
$$
FORECASTER BROWN
 

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