Tropical Storm NORMA

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TROPICAL STORM NORMA DISCUSSION NUMBER  10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2 AM PDT SUN SEP 25 2005
 
SHORTWAVE INFRARED IMAGERY AND A SERIES OF MICROWAVE SATELLITE
OVERPASSES INDICATE THAT THE CENTER OF NORMA IS EXPOSED TO THE
NORTHEAST OF A STRONG CONVECTIVE CLUSTER.  SATELLITE INTENSITY
ESTIMATES ARE 55 KT FROM TAFB...45 KT FROM AFWA...AND 35 KT FROM
SAB.  THE INITIAL INTENSITY IS REDUCED TO 45 KT BASED ON A BLEND OF
THESE ESTIMATES AND THE EXPOSED CENTER.  THIS INTENSITY IS IN GOOD
AGREEMENT WITH THE LATEST QUIKSCAT OVERPASS.

THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 325/5.  WATER VAPOR
IMAGERY SHOWS A MID/UPPER-LEVEL RIDGE EXTENDING WESTWARD FROM
MEXICO ALONG 24N 120W...WITH A DIGGING MID/UPPER-LEVEL TROUGH
EXTENDING FROM CALIFORNIA SOUTHWESTWARD TO NEAR 27N130W.  THIS
COMBINATION SHOULD STEER NORMA GENERALLY NORTHWESTWARD IN THE
SHORT TERM.  AFTER 48 HR OF SO...THE TROUGH SHOULD WEAKEN...
ALLOWING THE RIDGE TO BUILD WESTWARD AND TURN NORMA WESTWARD OR
WEST-SOUTHWESTWARD.  THE LARGE-SCALE MODELS ALL SHOW THIS
SCENARIO...AS DOES THE OFFICIAL FORECAST.  THE NEW TRACK FORECAST
IS SIMILAR TO...BUT NORTH OF AND A LITTLE FASTER THAN...THE
PREVIOUS FORECAST BASED MAINLY ON THE INITIAL POSITION AND MOTION. 
IT IS MORE OR LESS DOWN THE MIDDLE OF THE ENVELOPE OF GUIDANCE.

NORMAL IS IN AN ENVIRONMENT OF 20-25 KT EASTERLY SHEAR ACCORDING TO
ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN.  LARGE-SCALE
MODELS FORECAST THE SHEAR TO CONTINUE FOR 48-72 HR...WHICH SHOULD
PREVENT INTENSIFICATION AND POSSIBLY CAUSE FURTHER WEAKENING.  THE
SHEAR WILL LIKELY DECREASE AFTER 72 HR...BUT BY THAT TIME NORMA
SHOULD HAVE MOVED NORTH OF THE 26C SEA SURFACE TEMPERATURE
ISOTHERM.  THE INTENSITY FORECAST WILL CALL FOR SLOW WEAKENING FOR
THE FIRST 48 HR...FOLLOWED BY A FASTER WEAKENING OVER THE COOLER
WATERS.  THIS FORECAST IS A BLEND OF THE WEAKER SHIPS AND THE
STRONGER GFDL.

FORECASTER BEVEN
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      25/0900Z 17.4N 111.5W    45 KT
 12HR VT     25/1800Z 18.0N 111.9W    45 KT
 24HR VT     26/0600Z 18.9N 112.6W    45 KT
 36HR VT     26/1800Z 19.9N 113.6W    40 KT
 48HR VT     27/0600Z 20.7N 114.8W    40 KT
 72HR VT     28/0600Z 21.0N 116.5W    30 KT
 96HR VT     29/0600Z 20.5N 118.5W    25 KT...DISSIPATING
120HR VT     30/0600Z 20.0N 121.0W    20 KT...REMNANT LOW
 
 
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