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Tropical Storm ALVIN (Text)

ZCZC MIATCDEP1 ALL
TTAA00 KNHC DDHHMM
 
TROPICAL STORM ALVIN DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP012013
200 PM PDT WED MAY 15 2013
 
ASCAT DATA FROM AROUND 1612 UTC SHOWED THAT THE DEPRESSION HAD WINDS
VERY NEAR THE THRESHOLD FOR A TROPICAL STORM.  THE CLOUD PATTERN IN
VISIBLE IMAGERY HAS BECOME MORE ORGANIZED SINCE THE TIME OF THAT
PASS...AND IT IS LIKELY THAT THE SYSTEM HAS BECOME A TROPICAL
STORM.  THE INTENSITY IS BEING SET AT 35 KT.

THE ASCAT PASS ALSO HELPED TO BETTER LOCATE THE LOW-LEVEL
CENTER...AND THE INITIAL MOTION ESTIMATE IS NOW 290 DEGREES AT 11
KT.  ALVIN IS ON THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL RIDGE
THAT EXTENDS SOUTHWESTWARD FROM MAINLAND MEXICO OVER THE
PACIFIC...AND THIS FEATURE SHOULD CONTINUE TO STEER THE STORM
WEST-NORTHWESTWARD FOR THE NEXT FEW DAYS.  A MID-LEVEL TROUGH IS
FORECAST TO AMPLIFY NEAR CALIFORNIA COAST IN 2 TO 3 DAYS...CREATING
A WEAKNESS IN THE RIDGE.  THERE IS A SIGNIFICANT SPLIT IN THE MODEL
GUIDANCE WITH THE STRONGER GFS AND GFDL SHOWING A TURN TOWARD THE
NORTH AND THE WEAKER ECMWF AND UKMET MODELS SHOWING A CONTINUED
WESTWARD MOTION BY DAY 5.  THE OFFICIAL FORECAST SOMEWHAT SPLITS
THE DIFFERENCE BUT DOES FAVOR THE SCENARIO OF A STRONGER
NORTHWESTWARD-TURNING STORM.

MOST OF THE INTENSITY GUIDANCE SUPPORTS ALVIN REACHING HURRICANE
STRENGTH IN A FEW DAYS.  THE DYNAMICAL GFDL AND HWRF MODELS ARE THE
MOST AGGRESSIVE...BUT EVEN THE SHIPS MODEL SHOWS ALVIN GETTING
STRONGER THAN WE INDICATED IN THE PREVIOUS OFFICIAL FORECAST. 
ALVIN IS ABOUT TO MOVE OVER A WARM POOL OF WATER WITH SEA SURFACE
TEMPERATURES AROUND 30.5C...AND VERTICAL SHEAR SHOULD BE MINIMAL
FOR AT LEAST THE NEXT 3 DAYS.  THE NHC INTENSITY FORECAST CONTINUES
TO SHOW A STEADY INTENSIFICATION AND HAS BEEN BUMPED UP SLIGHTLY
FROM THE PREVIOUS FORECAST THROUGH DAY 3.  FASTER STRENGTHENING IS
POSSIBLE...AND THE RAPID INTENSIFICATION INDEX NOW SHOWS A 1 IN 3
CHANCE OF A 30-KT INCREASE IN WINDS OVER THE NEXT 24 HOURS. 
WEAKENING SHOULD BE UNDERWAY IN 4 TO 5 DAYS MAINLY DUE TO STRONGER
VERTICAL WIND SHEAR.

FORECAST POSITIONS AND MAX WINDS
 
INIT  15/2100Z  8.7N 105.1W   35 KT  40 MPH
 12H  16/0600Z  9.3N 106.5W   40 KT  45 MPH
 24H  16/1800Z 10.0N 108.2W   50 KT  60 MPH
 36H  17/0600Z 10.6N 109.8W   60 KT  70 MPH
 48H  17/1800Z 11.1N 111.4W   70 KT  80 MPH
 72H  18/1800Z 12.5N 114.0W   75 KT  85 MPH
 96H  19/1800Z 14.0N 116.0W   60 KT  70 MPH
120H  20/1800Z 15.5N 117.5W   40 KT  45 MPH
 
$$
FORECASTER BERG
 
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