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HURRICANE ALMA DISCUSSION NUMBER  18
NATIONAL WEATHER SERVICE MIAMI FL
8 PM PDT TUE MAY 28 2002
 
DURING THE PAST 12 HOURS OR SO...ALMA APPEARS TO HAVE GONE THROUGH A 
PERIOD OF RAPID INTENSIFICATION. THE INITIAL INTENSITY ESTIMATE OF 
75 KT IS BASED ON DVORAK SATELLITE INTENSITY ESTIMATES OF T4.5...OR 
77 KT...FROM BOTH TAFB AND AFWA... A 6 HOUR OBJECTIVE DVORAK 
T-NUMBER OF T4.5...AND A 28/2115Z AMSU EXPERIMENTAL INTENSITY 
ESTIMATE OF 86 KT. A RAGGED EYE FEATURE WAS EVIDENT EARLIER IN 
VISIBLE AND INFRARED IMAGERY FOR ABOUT 3 HOURS...BUT HAS NOW BECOME 
CLOUD COVERED DUE TO A BURST OF EYEWALL CONVECTION IN THE SOUTHERN 
SEMICIRCLE. HOWEVER...A 28/1726Z SSMI MICROWAVE OVERPASS CLEARLY 
INDICATED A WELL-DEFINED MID-LEVEL EYE...WHICH WOULD FURTHER SUPPORT 
THE INCREASE IN THE INITIAL INTENSITY.
 
THE INITIAL MOTION ESTIMATE IS 290/06 BASED ON THE LAST 12 HOURS OF 
MOTION. THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS TRACK 
FORECAST AND PHILOSOPHY. ALMA APPEARS TO BE ON TRACK...SO ONLY  
MINOR ADJUSTMENTS WERE MADE. THE BIGGEST QUESTION WILL BE HOW MUCH 
OF ALMA'S CIRCULATION REMAINS INTACT AFTER 48 HOURS WHEN THE CYCLONE 
PASSES AROUND THE SUBTROPICAL RIDGE AXIS AND BEGINS TO RECURVE TO 
THE NORTHEAST. THE 18Z AVN/GFS MODEL RUN INDICATES THE 200 MB LOW TO 
THE WEST OF BAJA AND THE ASSOCIATED SUBTROPICAL JETSTREAM TO ITS 
SOUTH WILL GRADUALLY LIFT NORTHWARD AND BE NORTH OF 20N LATITUDE BY 
72 HOURS. THE DECREASING VERTICAL SHEAR MAY ALLOW ALMA TO REMAIN 
VERTICALLY DEEP AND WEAKEN LESS...WHICH WOULD RESULT IN THE 
LOW-LEVEL CENTER TRACKING FASTER TO THE NORTHEAST THAN THE OFFICIAL 
FORECAST AND THE AVN/GFS MODEL ARE INDICATING. THE GFDL MODEL KEEPS 
ALMA AS A SIGNIFICANT CIRCULATION BEYOND 72 HOURS...AND THE OFFICIAL 
FORECAST TRACK IS A BLEND OF THE GFDL AND THE AVN/GFS SOLUTIONS.
 
ALMA SHOULD PEAK DURING THE NEXT 24 HOURS...IF NOT SOONER...AS THE 
SYSTEM TRACKS CLOSER TO COOLER SSTS AND ALSO BEGINS TO ENTRAIN 
LOW-LEVEL COLD AIR STRATOCUMULUS CLOUDS THAT ARE CURRENTLY LOCATED 
JUST WEST OF 116W LONGITUDE. THE OUTFLOW PATTERN REMAINS GOOD AND 
THE SHIPS INTENSITY MODEL INDICATES THE VERTICAL SHEAR IS EXPECTED 
TO REMAIN LESS THAN 15 KT THROUGHOUT THE PERIOD. AS SUCH...THE 
INTENSITY FORECAST WAS BUMPED UP A LITTLE DURING THE FIRST 24 
HOURS...WITH ONLY SLOW WEAKENING INDICATED AFTERWARDS...WHICH IS 
CLOSE TO THE SHIPS INTENSITY FORECAST TREND.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     29/0300Z 12.4N 114.0W    75 KTS
12HR VT     29/1200Z 13.0N 115.0W    85 KTS
24HR VT     30/0000Z 14.1N 115.8W    85 KTS
36HR VT     30/1200Z 15.3N 116.2W    75 KTS
48HR VT     31/0000Z 16.3N 116.2W    65 KTS
72HR VT     01/0000Z 18.0N 115.5W    50 KTS
 
 
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