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HURRICANE NARDA DISCUSSION NUMBER 7
NATIONAL WEATHER SERVICE MIAMI FL
8 PM PDT SUN OCT 21 2001
VISIBLE AND INFRARED SATELLITE IMAGERY INDICATE THAT NARDA HAS
CONTINUED TO RAPIDLY INTENSIFY. A SMALL CDO AND AN INTERMITTENT EYE
HAVE DEVELOPED DURING THE PAST 6 HOURS...AND A BURST OF VERY DEEP
EYEWALL CONVECTION HAS DEVELOPED DURING THE PAST 3 HOURS.
THEREFORE...THE INITIAL INTENSITY IS INCREASED TO 75 KT BASED ON A
DVORAK SATELLITE INTENSITY ESTIMATE OF 77 KT...T4.5...FROM TAFB PLUS
A 3-HOUR OBJECTIVE DVORAK INTENSITY OF 80 KT...ODT4.6. UPPER-LEVEL
OUTFLOW IS GOOD IN ALL QUADRANTS AND CONTINUES TO IMPROVE.
THE INITIAL MOTION ESTIMATE IS 300/09. THERE HAS BEEN SOME
SIGNIFICANT WOBBLES IN THE TRACK OVER THE PAST 6 TO 12 HOURS...
WHICH IS NOT UNUSUAL FOR RAPIDLY INTENSIFYING TROPICAL CYCLONES.
OTHERWISE...NARDA IS EXPECTED TO TRACK WEST-NORTHWEST OR SLIGHTLY
NORTHWESTWARD FOR THE NEXT 24 TO 36 HOURS AS IT BEGINS TO COME UNDER
THE INFLUENCE OF INCREASING MID- TO UPPER-LEVEL SOUTHWESTERLY FLOW
ON THE EAST SIDE OF THE DEEP MID-OCEANIC TROUGH CURRENTLY EXTENDING
SOUTHWARD ACROSS THE HAWAIIAN ISLANDS. NARDA IS FORECAST TO BECOME
SEVERELY SHEARED BY 48 HOURS AND DEGRADE INTO MORE OF A SHALLOW
SYSTEM BY...THUS BEING STEERED MORE WESTWARD BY THE STRONG LOW-LEVEL
EASTERLY FLOW ON THE SOUTHERN SIDE OF THE SUBTROPICAL HIGH TO ITS
NORTH. THE OFFICIAL FORECAST IS CLOSE TO THE PREVIOUS FORECAST
TRACK AND THE 21/12Z NOGAPS MODEL...BUT MUCH SLOWER AND A LITTLE
FARTHER NORTH THAN THE AVN AND UKMET SOLUTIONS.
NARDA APPEARS TO BE ABOUT 18 HOURS INTO ITS RAPID INTENSIFICATION
PERIOD. GIVEN THE DUAL OUTFLOW CHANNELS THAT EXISTS...THE RAPID
INTENSIFICATION PROCESS WOULD GENERALLY CONTINUE FOR ANOTHER 12
HOURS OR SO. HOWEVER...INCREASING VERTICAL SHEAR IN THE NEXT 12 TO
18 HOURS IS EXPECTED TO SUPPRESS THE INTENSIFICATION PROCESS. AS
SUCH...NARDA IS ONLY FORECAST TO REACH 85 KT...WHICH IS SIMILAR TO
THE LATEST GFDL AND SHIPS INTENSITY MODEL FORECASTS. BUT IF THE
VERTICAL SHEAR DOES NOT BECOME AS STRONG AS THE 25 TO 36 KT THAT THE
AVN MODEL IS FORECASTING...THEN NARDA COULD PEAK BETWEEN 90 AND 100
KT IN 12 TO 18 HOURS. BY 24 HOURS...THE CYCLONE IS EXPECTED TO
TRACK FAR ENOUGH WEST TO BE SEVERELY AFFECTED BY STRONG UPPER-LEVEL
WESTERLIES...WHICH SHOULD BRING ABOUT RAPID WEAKENING.
NARDA IS A FAIRLY COMPACT SYSTEM AND SINCE IT IS FORECAST TO PEAK IN
INTENSITY WITHIN 24 HOURS...THE WIND FIELD SHOULD HAVE LITTLE TIME
TO INCREASE. AS SUCH...THE WIND RADII WERE KEPT SMALLER THAN WHAT
WOULD TYPICALLY BE EXPECTED FOR AN 85 TO 90 KT HURRICANE.
FORECASTER STEWART
FORECAST POSITIONS AND MAX WINDS
INITIAL 22/0300Z 14.6N 131.8W 75 KTS
12HR VT 22/1200Z 15.5N 133.4W 85 KTS
24HR VT 23/0000Z 16.6N 135.7W 75 KTS
36HR VT 23/1200Z 17.5N 138.4W 65 KTS
48HR VT 24/0000Z 18.0N 141.1W 55 KTS
72HR VT 25/0000Z 18.5N 145.5W 40 KTS
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