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HURRICANE NARDA DISCUSSION NUMBER 8
NATIONAL WEATHER SERVICE MIAMI FL
2 AM PDT MON OCT 22 2001
DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB INDICATE THAT NARDA HAS
LEVELED OFF AT 75 KNOTS. AN AMSU CENTRAL PRESSURE ESTIMATE AT 22Z
WAS 996 MB...WEAKER THAN THE 77-KNOT/979-MB DVORAK ESTIMATES FOR
00Z. A QUIKSCAT PASS AT 0248Z DID NOT SHOW A CLOSED CIRCULATION AND
MEASURED HIGHEST WIND SPEEDS OF ONLY 50 KNOTS... CONTAMINATED OR
UNCONTAMINATED. FINALLY SSMI PASSES AT 0515Z AND 0613Z SHOW THE
LOW-LEVEL CIRCULATION DISPLACED TO THE SOUTHWEST EDGE OF THE DEEPEST
CONVECTION. BASED ON THE ABOVE...THE INITIAL WIND SPEED IS
DECREASED BY 5 KNOTS TO 70 KNOTS. THE SHIPS MODEL DIAGNOSES A
VERTICAL SHEAR OF 21 KNOTS BASED ON THE 00Z AVIATION MODEL ANALYSIS
AND FORECASTS 40 KNOTS OF SHEAR IN 24 HOURS. THE DISPLACED LOW
LEVEL CENTER SEEN IN THE SSMI IMAGERY SUGGESTS THAT THE VERTICAL
SHEAR HAS BEGUN TO AFFECT THE HURRICANE. CIMSS SATELLITE WIND SHEAR
ANALYSIS ALSO SHOWS A 20 KNOTS SHEAR ISOTACH DIRECTLY OVER NARDA.
THIS SHEAR IS NOT YET EVIDENT ON IR IMAGERY. THE INTENSITY FORECAST
ASSUMES THAT NARDA HAS PEAKED AND SHOULD BEGIN WEAKENING SOON.
THE INITIAL MOTION ESTIMATE IS 305/10 BASED ON A COMPROMISE INITIAL
POSTION BETWEEN THE 0515Z SSMI LOCATION AND 06Z IR FIXES.
MAINTAINING A WEAK MID LEVEL RIDGE TO THE NORTH OF NARDA...THE
AVIATION AND NOGAPS MODELS FORECAST A 275 AND 290 DEGREE HEADING AT
15 KNOTS OR SO UNTIL DISSIPATION IN 36 TO 48 HOURS. THE GFDL IS
MUCH SLOWER AND A LITTLE FURTHER NORTH. THE OFFICIAL FORECAST IS A
BLEND OF THESE MODELS AND IS JUST A LITTLE TO THE RIGHT OF THE
PREVIOUS ADVISORY AND A LITTLE SLOWER.
FORECASTER LAWRENCE
FORECAST POSITIONS AND MAX WINDS
INITIAL 22/0900Z 15.5N 132.7W 70 KTS
12HR VT 22/1800Z 16.4N 134.0W 70 KTS
24HR VT 23/0600Z 17.3N 136.2W 65 KTS
36HR VT 23/1800Z 17.9N 138.2W 55 KTS
48HR VT 24/0600Z 18.5N 140.4W 40 KTS
72HR VT 25/0600Z 19.0N 144.0W 30 KTS
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