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TROPICAL STORM ALMA DISCUSSION NUMBER 14
NATIONAL WEATHER SERVICE MIAMI FL
8 PM PDT MON MAY 27 2002
THE LOW-LEVEL CIRCULATION CENTER REMAINS DIFFICULT TO LOCATE AS
INDICATED BY THE LARGE SPREAD BETWEEN FIX POSITIONS FROM THE VARIOUS
SATELLITE AGENCIES. THEREFORE...THE INITIAL POSITION IS BASED ON
PERSISTENCE...EXTRAPOLATION...AND CONTINUITY WITH THE PREVIOUS
FORECAST TRACK...WHICH PLACES THE CENTER JUST NORTH OF WHAT APPEARS
TO BE A SMALL CDO FEATURE DEVELOPING. THE INITIAL INTENSITY OF 50 KT
IS BASED ON DVORAK SATELLITE INTENSITY ESTIMATES OF T3.5...55 KT...
FROM BOTH TAFB AND SAB...BUT WAS KEPT SLIGHTLY LOWER DUE TO THE
UNCERTAINTY IN THE EXACT LOCATION OF THE LOW-LEVEL CENTER.
THE INITIAL MOTION ESTIMATE IS 285/8. ALMA IS EXPECTED TO CONTINUE
TRACKING IN A GENERAL WEST-NORTHWESTWARD DIRECTION AROUND THE
PERIPHERY OF THE MEXICAN SUBTROPICAL RIDGE. ONCE THE CYCLONE REACHES
ABOUT 115W LONGITUDE...THE RIDGE TO THE NORTH IS FORECAST TO WEAKEN
AS ALLUDED TO IN THE PREVIOUS FORECAST DISCUSSIONS. THE 18Z AVN/GFS
AND GFDL MODEL RUNS ARE STILL INDICATING THAT THIS WILL OCCUR AS A
MID- TO UPPER-LEVEL TROUGH/LOW DEVELOPS JUST WEST OF BAJA
CALIFORNIA. THE UKMET SCENARIO IS SIMILAR...BUT MUCH FASTER AND
TAKES ALMA ALMOST DUE NORTH IN 12 HOURS. THE UKMET SOLUTION SEEMS
EXCESSIVE GIVEN THE STRONG RIDGE TO THE NORTH AND WAS THEREFORE
REJECTED. THE GFDL IS A LITTLE EAST OF THE AVN AND AVN ENSEMBLE
SOLUTIONS...BUT SHOWS THE SAME GRADUAL RECURVATURE TREND AFTER 48
HOURS. THE OFFICIAL FORECAST TRACK IS A TAD TO THE LEFT OF THE
PREVIOUS FORECAST TRACK...BUT TO THE RIGHT OF THE AVN TRACK.
BANDING FEATURES HAVE CONTINUED TO IMPROVE DURING THE DAY AND A
SMALL CDO FEATURE MAY BE DEVELOPING. OUTFLOW REMAINS GOOD IN THE
WESTERN SEMICIRCLE AND IS IMPROVING TO THE EAST. GRADUAL
INTENSIFICATION TO 75 KT IN 36 HOURS IS FORECAST BY THE SHIPS
INTENSITY MODEL...WHILE THE GFDL RAPIDLY STRENGTHENS THE CYCLONE TO
95 KT IN 24 HOURS. THE GFDL SOLUTION SEEMS EXCESSIVE GIVEN THE LACK
OF ANY PERSISTENT CENTRAL DEEP CONVECTION DURING THE PAST 48 HOURS.
HOWEVER...ALMA IS EXPECTED TO REMAIN IN A LOW SHEAR ENVIRONMENT AND
OVER 28-29C SSTS FOR THE NEXT 24 TO 36 HOURS...SO AT LEAST STEADY
INTENSIFICATION SEEMS LIKELY AND ALMA IS FORECAST TO BECOME A
HURRICANE WITHIN 24 HOURS. BY 48 HOURS...THE CYCLONE IS EXPECTED TO
BE MOVING OVER COOLER SSTS AND ENCOUNTER INCREASING SOUTHWESTERLY
UPPER-LEVEL SHEAR...WHICH SHOULD ACT TO CAP THE INTENSIFICATION
PROCESS AND BRING ABOUT GRADUAL WEAKENING BY 72 HOURS. HOWEVER...IF
A CDO DOES DEVELOP DURING THE NEXT 6 TO 12 HOURS...THEN THE
INTENSITY FORECAST THROUGH 48 HOURS WILL PROBABLY BE TOO LOW.
FORECASTER STEWART
FORECAST POSITIONS AND MAX WINDS
INITIAL 28/0300Z 11.6N 110.7W 50 KTS
12HR VT 28/1200Z 12.0N 111.8W 60 KTS
24HR VT 29/0000Z 12.6N 113.1W 70 KTS
36HR VT 29/1200Z 13.4N 114.4W 80 KTS
48HR VT 30/0000Z 14.7N 115.3W 80 KTS
72HR VT 31/0000Z 18.0N 115.0W 70 KTS
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