Tropical Storm LOWELL

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TROPICAL STORM LOWELL DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP132008
800 PM PDT SUN SEP 07 2008
 
ALTHOUGH LOWELL HAS BEEN EXPERIENCING MODERATE EASTERLY SHEAR...DEEP
CONVECTION HAS CONTINUED TO INCREASE AND NOW COMPLETELY COVERS THE
PREVIOUSLY EXPOSED LOW-LEVEL CENTER. THE DVORAK INTENSITY ESTIMATE
AT 00Z FROM BOTH TAFB AND SAB WAS T3.0/45 KT. HOWEVER...DURING THE
PAST 2 HOURS SINCE THAT SATELLITE FIX...DATA T-NUMBERS HAVE
INCREASED TO T3.5/55 KT AS THE CENTER HAS BECOME EMBEDDED FARTHER
INTO THE EASTERN PORTION OF THE CONVECTIVE CLOUD MASS. THEREFORE
...THE INITIAL INTENSITY IS INCREASED TO 50 KT FOR THIS ADVISORY.
 
THE INITIAL MOTION ESTIMATE IS 295/10. LOWELL HAS MADE A SLIGHT
WESTWARD JOG PROBABLY IN RESPONSE TO THE DEVELOPMENT OF THE DEEP
CONVECTION OVER THE CENTER...WHICH HAS VERTICALLY INCREASED THE
VORTEX UP TO THE 200 MB LEVEL WHERE MODERATE EASTERLY WINDS EXIST.
OTHER THAN THIS SHORT TERM WOBBLE TO THE LEFT OF THE PREVIOUS TRACK
...THE PREVIOUS FORECAST TRACK AND REASONING REMAINS UNCHANGED. ALL
OF THE GLOBAL MODELS AGREE THAT AN UPPER-LEVEL TROUGH/LOW CURRENTLY
OVER NORTHERN CALIFORNIA WILL DIG SOUTHWARD AND ERODE THE
MID-/UPPER-LEVEL RIDGE TO THE NORTH OF LOWELL BY 48-72 HOURS. THIS
IS EXPECTED TO WEAKEN THE STEERING FLOW AND PERMIT LOWELL TO SLOWLY
RECURVE TO THE NORTHEAST TOWARD SOUTHERN BAJA CALIFORNIA. THE
OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK AND IS A
LITTLE TO THE LEFT...OR WEST...OF THE NHC MODEL CONSENSUS.

THE VERTICAL SHEAR ACROSS LOWELL IS FORECAST TO GRADUALLY WEAKEN TO
LESS THAN 10 KT BY 36 HOURS...WHILE REMAINING OVER SSTS OF AT LEAST
27C. THE MID-LEVEL ENVIRONMENT IS ALSO FORECAST TO REMAIN QUITE
MOIST WITH RELATIVE HUMIDITY VALUES OF MORE THAN 70 PERCENT. THESE
CONDITIONS WOULD TYPICALLY INDICATE THAT SOME DEGREE OF
STRENGTHENING IS LIKELY. HOWEVER...THE SHIPS MODEL STEADILY
DECREASES LOWELL'S INTENSITY AND MAKES THE CYCLONE A DEPRESSION BY
96 HOURS. GIVEN THE FAVORABLE CONDITIONS DESCRIBED ABOVE...THE
OFFICIAL INTENSITY FORECAST IS HELD HIGHER THAN THE SHIPS MODEL AND
IS SIMILAR TO THE HWRF MODEL...WHICH MAKES LOWELL A CATEGORY 1
HURRICANE BY 24 HOURS BEFORE SLOWLY WEAKENING IT.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      08/0300Z 18.2N 109.8W    50 KT
 12HR VT     08/1200Z 18.9N 110.9W    55 KT
 24HR VT     09/0000Z 19.9N 112.3W    55 KT
 36HR VT     09/1200Z 20.7N 113.3W    60 KT
 48HR VT     10/0000Z 21.6N 113.7W    60 KT
 72HR VT     11/0000Z 22.8N 113.3W    55 KT
 96HR VT     12/0000Z 24.0N 112.0W    50 KT...NEAR SOUTHWEST BAJA
120HR VT     13/0000Z 25.0N 110.5W    35 KT...OVR SRN GULF OF CALIF
 
$$
FORECASTER STEWART
 
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