Tropical Storm OTIS

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TROPICAL STORM OTIS DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
8 AM PDT THU SEP 29 2005
 
A LARGE BURST OF CONVECTION WITH CLOUD TOPS COLDER THAN -80C
DEVELOPED EARLY THIS MORNING OVER AND SOUTHWEST OF THE CENTER. A
29/0912Z AMSR-E MICROWAVE OVERPASS INDICATED A LARGE CURVED BAND
THAT WRAPPED MORE THAN HALF WAY AROUND THE MID-LEVEL CIRCULATION
CENTER... WITH AN EXPOSED LOW-LEVEL CENTER LOCATED NEAR THE
SOUTHERN TIP OF THE CONVECTIVE BAND. DVORAK INTENSITY ESTIMATES AT
12Z WERE 45 KT FROM TAFB AND SAB... AND 35 KT FROM AFWA. SINCE THAT
TIME... HOWEVER... CLOUD TOPS HAVE WARMED AND THE BANDING FEATURES
HAVE BECOME LESS DISTINCT. THEREFORE... THE INTENSITY HAS ONLY BEEN
INCREASED TO 40 KT FOR THIS ADVISORY.
 
THE INITIAL MOTION ESTIMATE IS 305/08. AS MENTIONED IN PREVIOUS
DISCUSSIONS... THE EXACT CENTER REMAINS DIFFICULT TO DETERMINE. THE
AFOREMENTIONED AMSR-E OVERPASS DID DEPICT A NICE LOW-LEVEL
CIRCULATION... BUT OVER THE PAST 24 HOURS THERE HAVE BEEN MULTIPLE
SWIRLS GENERATED IN THE DEEP CONVECTION TO THE WEST THAT HAVE THEN
ROTATED CYCLONICALLY AROUND THE MID-LEVEL CIRCULATION CENTER. THE
ADVISORY POSITION IS BASED ON A BLEND OF THE MID-LEVEL AND
LOW-LEVEL CENTERS NOTED IN MICROWAVE DATA... WHICH ALSO MAINTAINS
CONTINUITY WITH THE PREVIOUS MOTION AND FORECAST TRACK. OTIS IS
EXPECTED TO GRADUALLY MOVE WEST-NORTHWESTWARD AROUND THE
SOUTHWESTERN PERIPHERY OF A LARGE MID-LEVEL SUBTROPICAL RIDGE
ORIENTED EAST-WEST ACROSS NORTHERN MEXICO AND BAJA CALIFORNIA. THE
WESTERN PORTION OF THE RIDGE OVER BAJA CALIFORNIA IS FORECAST BY
ALL THE MODELS TO BE ERODED BY A SOUTHWARD-MOVING SHORTWAVE TROUGH
AFTER 72 HOURS... WHICH SHOULD ALLOW OTIS TO TURN NORTHWARD ACROSS
BAJA BY 120 HOURS. ONLY THE 29/00Z ECMWF MODEL TURNS OTIS AWAY FROM
THE BAJA PENINSULA. THE OFFICIAL FORECAST TRACK IS CLOSE TO THE
PREVIOUS TRACK AND THE NHC MODEL CONSENSUS... MINUS THE ECMWF.
 
NORTHEASTERLY UPPER-LEVEL SHEAR CONTINUES TO SLOWLY ABATE ACROSS
OTIS AND THIS TREND IS FORECAST TO CONTINUE THROUGH 72 HOURS.
HOWEVER... SOME MID-LEVEL SHEAR UNDERCUTTING THE IMPROVING OUTFLOW
LAYER APPEARS TO BE AFFECTING THE CYCLONE AND LIKELY WILL NOT
WEAKEN FOR ANOTHER 24 HOURS. BUT WITH THE IMPROVING OUTFLOW PATTERN
...WEAK VERTICAL SHEAR... AND SSTS OF 28-29C BENEATH THE STORM...
AT LEAST MODEST STRENGTHENING SHOULD OCCUR UNTIL COOLER WATER IS
REACHED AFTER 72 HOURS. THE OFFICIAL INTENSITY FORECAST IS A BLEND
OF THE SHIPS AND GFDL MODELS... WHICH BRING OTIS UP TO 63 KT AND 74
KT... RESPECTIVELY... BY 48 HOURS.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      29/1500Z 17.9N 108.2W    40 KT
 12HR VT     30/0000Z 18.7N 109.2W    45 KT
 24HR VT     30/1200Z 19.5N 110.5W    55 KT
 36HR VT     01/0000Z 20.1N 111.3W    65 KT
 48HR VT     01/1200Z 20.8N 111.9W    70 KT
 72HR VT     02/1200Z 21.9N 112.5W    65 KT
 96HR VT     03/1200Z 24.5N 113.5W    50 KT
120HR VT     04/1200Z 28.5N 114.0W    35 KT...INLAND OVER BAJA

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