TROPICAL STORM NIALA FORMS SOUTHEAST OF THE HAWAIIAN ISLANDS...
SUMMARY OF 500 AM HST...1500 UTC...INFORMATION
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LOCATION...15.1N 150.1W
ABOUT 460 MI...735 KM SE OF HILO HAWAII
ABOUT 665 MI...1075 KM SE OF HONOLULU HAWAII
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...NW OR 320 DEGREES AT 7 MPH...11 KM/H
MINIMUM CENTRAL PRESSURE...1002 MB...29.59 INCHES
WATCHES AND WARNINGS
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THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT.
INTERESTS IN THE MAIN HAWAIIAN ISLANDS SHOULD MONITOR THE PROGRESS
OF TROPICAL STORM NIALA. A TROPICAL STORM WATCH MAY BR REQUIRED FOR
THE BIG ISLAND LATER TODAY OR TONIGHT.
DISCUSSION AND 48-HOUR OUTLOOK
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AT 500 AM HST...1500 UTC...THE CENTER OF TROPICAL STORM NIALA WAS
LOCATED NEAR LATITUDE 15.1 NORTH...LONGITUDE 150.1 WEST. NIALA IS
MOVING TOWARD THE NORTHWEST NEAR 7 MPH...11 KM/H. THIS GENERAL
MOTION IS EXPECTED TO CONTINUE THROUGH THIS EVENING...WITH A
GRADUAL TURN TOWARD THE WEST-NORTHWEST FROM LATE TONIGHT THROUGH
SATURDAY. NIALA IS FORECAST TO TURN TOWARD THE WEST FROM SATURDAY
NIGHT INTO EARLY SUNDAY MORNING.
MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH...65 KM/H...WITH HIGHER
GUSTS. SOME ADDITIONAL INTENSIFICATION IS EXPECTED DURING THE NEXT
COUPLE OF DAYS.
TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 75 MILES...120 KM
FROM THE CENTER.
A 0745Z ASCAT PASS SHOWED A BROAD SWATH OF 35 KT SURFACE WINDS IN THE NORTHEAST AND EAST QUADRANTS OF SIX-C. INFRARED SATELLITE IMAGERY SHOWS A MUCH BETTER DEFINED TROPICAL SYSTEM THAN WE WERE SEEING THURSDAY EVENING. AS A RESULT...THE SUBJECTIVE DVORAK FIXES FROM JTWC...SAB AND PHFO WERE UNANIMOUS WITH CURRENT INTENSITY ESTIMATES OF 2.5/35 KT. THE 1330Z ADT ESTIMATE PROVIDED BY UW-CIMSS IS 2.3/33 KT. THEREFORE...WE HAVE UPGRADED TROPICAL DEPRESSION SIX-C TO A 35 KT TROPICAL STORM. THE DESIGNATED NAME FOR THIS SYSTEM IS NIALA...PRONOUNCED NEE-AH-LA. THE INITIAL MOTION OF TROPICAL STORM NIALA IS 320/6 KT. THE NEWLY FORMED TROPICAL STORM IS MOVING SLOWLY NORTHWESTWARD TOWARDS A WEAKNESS IN THE SUBTROPICAL RIDGE. THIS GENERAL MOTION IS EXPECTED TO CONTINUE DURING THE NEXT 12 HOURS...WITH A GRADUAL TURN TOWARD THE WEST-NORTHWEST AT ABOUT THE SAME SPEED BETWEEN 12 AND 36 HOURS. A LARGE MIDDLE AND UPPER LEVEL LOW PRESSURE SYSTEM CURRENTLY FAR NORTHEAST OF THE MAIN HAWAIIAN ISLANDS IS FORECAST TO SHIFT SOUTHEASTWARD. AN ASSOCIATED DEEP LAYER TROUGH IS FORECAST TO EXTEND SOUTHWEST FROM THE LOW ALOFT. THIS TROUGH ALOFT WILL LIKELY MOVE SOUTHWARD...WHICH WILL PRODUCE STRONG UPPER LEVEL SOUTHWESTERLY WINDS...AND INCREASING VERTICAL WIND SHEAR IN THE VICINITY OF NIALA. THE GLOBAL FORECAST MODELS CONTINUE TO SUGGEST THIS INCREASING VERTICAL WIND SHEAR WILL LIKELY WEAKEN AND DECOUPLE THE SYSTEM BEYOND DAY 3. AS A RESULT...THE WEAKENED SHALLOW CYCLONIC CIRCULATION THAT REMAINS AFTER THE SYSTEM IS SHEARED WILL LIKELY BE TRANSPORTED WESTWARD BY THE LOWER LEVEL STEERING FLOW. THE RELIABLE DYNAMICAL MODELS REMAIN IN GENERAL AGREEMENT WITH THIS SCENARIO WITH THE MAIN DIFFERENCES BEING THE FORWARD SPEED DURING DAYS 3 TO 5 AFTER THIS DECOUPLING OCCURS. THE LATEST TRACK FORECAST IS VERY CLOSE TO THE PREVIOUS WITH SOME SLIGHT ADJUSTMENTS TO NUDGE THE TRACK CLOSER TO THE TVCN AND GFEX CONSENSUS GUIDANCE. TROPICAL STORM NIALA IS PASSING OVER VERY WARM WATERS OF ABOUT 29C BASED ON THE LATEST SEA SURFACE TEMPERATURE ANALYSIS. IN ADDITION... THE CIRA ANALYSIS OF OCEAN HEAT CONTENT SHOWS THESE VALUES INCREASING ALONG THE FORECAST TRACK DURING THE NEXT COUPLE OF DAYS. HOWEVER...THE MOST RECENT GUIDANCE FOR CURRENT VERTICAL WIND SHEAR IN THE VICINITY OF NIALA FROM UW-CIMSS AND SHIPS SUGGEST THAT THERE IS SHEAR OF 13 TO 17 KT FROM THE WEST. THE SHEAR MAGNITUDE IS EXPECTED TO REMAIN ABOUT THE SAME DURING THE NEXT 36 HOURS. THE SHEAR IS FORECAST TO INCREASE...ESPECIALLY STARTING ON DAY 2...WHICH WILL EVENTUALLY BEGIN TO DECOUPLE THE SYSTEM. UNTIL THAT OCCURS...IT APPEARS THAT THE TROPICAL CYCLONE WILL BE ABLE TO INTENSIFY SLIGHTLY. THE LATEST INTENSITY FORECAST HAS BEEN NUDGED UPWARD DURING THE NEXT 2 DAYS. STEADY WEAKENING IS FORECAST BEYOND 48 HOURS...WITH NIALA WEAKENING TO A TROPICAL DEPRESSION...AND POSSIBLY A REMNANT LOW BY DAYS 4 AND 5. NOTE THAT THE WIND RADII WERE ADJUSTED BASED ON THE 0745Z ASCAT PASS. THESE LARGER WIND RADII HAVE CAUSED THE MOST RECENT TROPICAL CYCLONE WIND SPEED PROBABILITIES TO INCREASE OVER THE EXTREME SOUTHERN END OF THE BIG ISLAND. AS A RESULT...A TROPICAL STORM WATCH MAY BE REQUIRED FOR THE BIG ISLAND LATER TODAY OR TONIGHT. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 15.1N 150.1W 35 KT 40 MPH 12H 26/0000Z 15.9N 151.1W 40 KT 45 MPH 24H 26/1200Z 16.7N 152.4W 45 KT 50 MPH 36H 27/0000Z 17.0N 153.8W 45 KT 50 MPH 48H 27/1200Z 17.0N 155.1W 40 KT 45 MPH 72H 28/1200Z 17.0N 157.0W 35 KT 40 MPH
