Hurricane SERGIO

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HURRICANE SERGIO DISCUSSION NUMBER  11
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP212006
100 AM PST THU NOV 16 2006
 
THE SATELLITE SIGNATURE OF SERGIO HAS CONTINUED TO SLOWLY DEGRADE...
WITH THE OVERALL CLOUD PATTERN ELONGATED FROM SOUTH TO NORTH AND
THE CENTRAL CONVECTION SOMEWHAT RAGGED.  AN SSM/I OVERPASS AT 0249Z
SHOWED THE BULK OF THE CONVECTION NORTHEAST OF THE CENTER. 
ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN NOW SHOW ABOUT
15 KT OF WESTERLY SHEAR AFFECTING THE SYSTEM DUE TO A DEVELOPING
MID/UPPER-LEVEL TROUGH WEST OF THE HURRICANE.  SATELLITE INTENSITY
ESTIMATES ARE 102 KT FROM TAFB...90 KT FROM SAB...AND 77 KT FROM
AFWA.  BASED ON THIS THE INITIAL INTENSITY REMAINS 90 KT...ALTHOUGH
THIS COULD BE A LITTLE GENEROUS.

SERGIO APPEARS TO BE MAKING ITS FORECAST LEFT TURN...WITH THE
INITIAL MOTION NOW 045/3.  WATER VAPOR IMAGERY SHOWS A
MID/UPPER-LEVEL LOW DEVELOPING OVER SOUTHERN BAJA CALIFORNIA WITH A
BROAD TROUGH EXTENDING SOUTHWARD TO NEAR 12N111W.  THE LARGE-SCALE
MODELS AGREE THE LOW SHOULD MOVE SOUTHWARD FOR ANOTHER 24 HR OR
SO...THEN TURN WESTWARD AS A MID/UPPER-LEVEL RIDGE BUILDS OVER
NORTHWESTERN MEXICO TO THE WEST OF A DEEP-LAYER TROUGH OVER THE
EASTERN UNITED STATES AND THE GULF OF MEXICO.  DESPITE THIS...A
CONSIDERABLE SPREAD REMAINS IN THE MODEL FORECAST TRACKS FOR
SERGIO.  THE GFDL AND THE NOGAPS ARE ON THE RIGHT SIDE OF THE
GUIDANCE ENVELOPE AND ARE THE FASTEST...BRINGING THE CENTER TO THE
MEXICAN COAST IN 48-72 HR.  THE GFS AND ECMWF ARE ON THE LEFT SIDE
OF THE GUIDANCE...WHILE THE UKMET IS DOWN THE MIDDLE AND SLOWER. 
THE FORECAST TRACK IS BASED ON THE PREMISE THAT THE DEVELOPING LOW
WILL TURN SERGIO NORTHWARD FOR 24 HR OR SO...FOLLOWED BY A MOTION
TOWARD THE NORTH-NORTHWEST OR NORTHWEST AS THE RIDGE BUILDS.  THE
NEW TRACK IS SIMILAR TO THE PREVIOUS FORECAST AND IS IN BEST
AGREEMENT WITH THE FLORIDA STATE SUPERENSEMBLE.  GIVEN THE
UNCERTAINTY...INTERESTS ALONG THE SOUTHWESTERN COAST OF MEXICO
SHOULD MONITOR THE PROGRESS OF SERGIO IN CASE IT MOVES CLOSER TO
THE COAST THAN CURRENTLY FORECAST.

THE LARGE-SCALE MODELS FORECAST THE SHEAR TO INCREASE SOMEWHAT OVER
THE NEXT 24 HR...SO THE INTENSITY FORECAST NOW CALLS FOR WEAKENING
DURING THAT PERIOD.  THE MODELS FORECAST AN UPPER-LEVEL RIDGE TO
BUILD OVER SERGIO FROM 24-72 HR...WHICH WILL CAUSE SOME SHEAR BUT
LIKELY PRODUCE STRONG DIFFLUENCE OR DIVERGENCE OVER THE SYSTEM. 
THE SHIPS AND SUPERENSEMBLE MODELS FORECAST WEAKENING DURING THIS
TIME...WHILE THE GFDL MAINTAINS SERGIO AS A 90-100 KT HURRICANE. 
ON THE PREMISE THAT THE SHEAR WILL PREVAIL OVER THE DIVERGENCE...
THE INTENSITY FORECAST WILL CALL FOR SLOW WEAKENING DURING THIS
TIME...ALTHOUGH AT A SLOWER PACE THAN THE PREVIOUS FORECAST.  AFTER
72 HR...THE SHEAR IS FORECAST TO INCREASE WHILE THE DIVERGENCE
DECREASES...WHICH SHOULD CAUSE A FASTER WEAKENING.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      16/0900Z 12.5N 103.1W    90 KT
 12HR VT     16/1800Z 13.1N 103.0W    85 KT
 24HR VT     17/0600Z 14.1N 103.3W    80 KT
 36HR VT     17/1800Z 15.0N 103.9W    80 KT
 48HR VT     18/0600Z 15.9N 104.8W    75 KT
 72HR VT     19/0600Z 18.0N 106.5W    70 KT
 96HR VT     20/0600Z 19.5N 107.5W    55 KT
120HR VT     21/0600Z 21.0N 110.0W    40 KT
 
$$
FORECASTER BEVEN
 
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