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HURRICANE ALMA DISCUSSION NUMBER 26
NATIONAL WEATHER SERVICE MIAMI FL
8 PM PDT THU MAY 30 2002
ALMA HAS BEEN SHOWING SIGNS OF SIGNIFICANT WEAKENING DURING THE PAST
6 HOURS. THE INNER-CORE CONVECTION HAS BECOME RAGGED AND ELONGATED
NORTHEAST-SOUTHWEST...WHILE THE EYE HAS DISAPPEARED IN BOTH VISIBLE
AND INFRARED IMAGERY. THE INITIAL INTENSITY OF 85 KT IS BASED ON A
BLEND OF DVORAK SATELLITE INTENSITY ESTIMATES RANGING FROM 77 KT TO
102 KT FROM BOTH TAFB AND SAB...AND 6-HOUR ODT AVERAGE T-NUMBERS
RANGING FROM T4.7/81 KT CDO AND T5.1/92 KT EYE PATTERNS. OUTFLOW
REMAINS GOOD TO THE NORTHEAST...BUT POOR AND/OR RESTRICTED ELSEWHERE
DUE TO MODERATE UPPER-LEVEL SOUTHWESTERLY SHEAR.
THE INITIAL MOTION ESTIMATE REMAINS 005/08. ALMA REMAINS ON TRACK SO
THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OTHER
THAN TO SHIFT IT SLIGHTLY NORTHWARD AFTER 36 HOURS. THE UPPER-LEVEL
LOW SOUTHWEST OF SAN DIEGO CONTINUES TO LIFT NORTHWARD...WHICH IS
ALLOWING THE SUBTROPICAL RIDGE TO ALSO SHIFT SLOWLY NORTHWARD. AS
SUCH...THE TRACK OF ALMA IS EXPECTED TO BE A LITTLE FARTHER NORTH
THAN PREVIOUSLY EXPECTED. THE UKMET...AVN/GFS...AND NOGAPS MODELS
WANT TO RAPIDLY WEAKEN ALMA AND MAKE IT STATIONARY IN 12 TO 24 HOURS
AND THEN GRADUALLY DRIFT IT SOUTHWARD. HOWEVER...ALMA HAS A HISTORY
OF BEING STRONGER THAN WHAT ANY OF THE FORECAST MODELS HAVE BEEN
FORECASTING...SO I THINK THIS CYCLONE WILL STICK AROUND A LITTLE
LONGER THAN WHAT THE MAJORITY OF THE MODELS ARE SUGGESTING. THE
OFFICIAL TRACK IS BETWEEN THE AVN/GFS MODEL AND THE AVN/GFS
10-MEMBER ENSEMBLE MEAN...AND CLOSE TO THE NAVY COAMPS AND THE DEEP
BAM MODELS.
DURING THE PAST 9 HOURS...WATER VAPOR AND VISIBLE SATELLITE IMAGERY
INDICATE A HIGH-LEVEL TROUGH...PROBABLY ABOVE 200 MB...HAS TRAVERSED
HURRICANE ALMA FROM SOUTHWEST TO NORTHEAST AND DISRUPTED THE
INNER-CORE CONVECTION. HOWEVER...THIS TROUGH AND ITS ASSOCIATED
VERTICAL SHEAR IS EXITING THE EASTERN SEMICIRCLE AND SOME OF THE
EYEWALL CONVECTION HAS STARTED TO MAKE A COMEBACK DURING THE PAST
HOUR OR SO. AS SUCH...ALMA MAY MAINTAIN SOME OF ITS INTENSITY FOR
THE NEXT 6 HOURS OR SO AS IT ENTERS THE DIURNAL CONVECTIVE MAXIMUM
PERIOD...DESPITE MOVING OVER SUB-25C SSTS NOW. THEREFORE...THE
PREVIOUS INTENSITY FORECAST AND WEAKENING TREND WERE MAINTAINED...
WHICH IS A LITTLE HIGHER THAN THE SHIPS AND GFDL INTENSITY MODELS.
FORECASTER STEWART
FORECAST POSITIONS AND MAX WINDS
INITIAL 31/0300Z 17.9N 115.0W 85 KTS
12HR VT 31/1200Z 18.8N 114.9W 75 KTS
24HR VT 01/0000Z 19.4N 114.6W 60 KTS
36HR VT 01/1200Z 19.7N 114.2W 45 KTS
48HR VT 02/0000Z 19.8N 113.7W 35 KTS
72HR VT 03/0000Z 20.0N 112.8W 25 KTS...DISSIPATING
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