WTPA42 PHFO 200853
TCDCP2

TROPICAL STORM IOKE DISCUSSION NUMBER   2
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   CP012006
1100 PM HST SAT AUG 19 2006

ONE-C CONTINUED TO ORGANIZE DURING THE EVENING AND APPEARS TO HAVE
STRENGTHENED ENOUGH TO AQUIRE A NAME. THAT NAME IS IOKE AND IT IS
THE FIRST NAMED SYSTEM IN THE CENTRAL PACIFIC SINCE HUKO BACK IN
LATE 2002. IOKE IS ROUGHLY TRANSLATED INTO ENGLISH AS JOYCE.

THE UPGRADE WAS DUE TO DVORAK FIXES FROM CPHC...JTWC AND AIR FORCE 
GLOBAL ALL WITH A DT OF 2.5. THAT TRANSLATES INTO ROUGHLY 35KT. WE 
ALSO HAD A WELL TIMED QUIKSCAT PASS RIGHT OVER THE SYSTEM AND IT 
SHOWED A NUMBER OF 35KT WINDS WITH EVEN A FEW 40KTS THROWN IN FOR 
GOOD MEASURE. WAS A LITTLE SUPRISING THAT THE STRONGEST WINDS WERE 
GENERALLY ON THE SOUTHERN SIDE OF THE STORM...WOULD EXPECT THE 
OPPOSITE. STRONGER WINDS ON SOUTH SIDE LIKELY DUE TO A STEEP 
PRESSURE GRADIENT BETWEEN IOKE AND THE ITCZ TO THE SOUTH. THAT 
SHOULD CHANGE AS IT MOVES FARTHER AWAY FROM THE ITCZ. THE WINDS 
WERE ALSO IN RAIN FLAGGED AREAS...BUT TYPICALLY WITH WIND SPEEDS IN 
THE 30-40KT RANGE...THIS MEANS THE ACTUAL WINDS WERE A BIT STRONGER. 

THE TD ONE-C SYSTEMS WE HAD IN 2003...04 AND 05 ONLY LASTED FOR A 
DAY AS THEY COULD NOT ESCAPE THE ITCZ AND WERE OVERWHELMED BY ITCZ 
CONVECTION. IOKE APPEARS TO BE OVERCOMING THE ITCZ AS THERE IS NO 
SUBSTANTIAL ITCZ CONVECTION WITHIN 10 DEGREES OF IOKE. IOKE ALSO  
APPEARS TO BE IN A PRIME SPOT FOR DEVELOPMENT. SHEAR ALOFT IS LESS 
THAN 10KT AND SSTS ARE OVER 28C. LAST HOUR OR TWO LOOKS LIKE 
CONVECTION DEVELOPING NEAR THE CENTER. IF THIS CAN DEVELOP MORE 
OVERNIGHT AND INTO THE MORNING WE COULD SEE A RAPIDLY DEVELOPING 
STORM...EVEN MORE SO THAN CURRENTLY FORECAST. 

IOKE IS EMBEDDED IN A DEEP LAYER FLOW THAT SHOULD MOVE THE STORM OFF 
TO THE WEST-NORTHWEST THRU 48 HOURS. MODEL GUIDANCE IS ALSO TIGHTLY 
CLUSTERED ALONG SUCH A TRACK. SO HAVE MADE NO CHANGES IN THE 
FORECAST THRU THAT POINT. AFTER THAT TIME THERE IS MORE GUIDANCE 
SPREAD AS GLOBAL MODELS INDICATING A SUBSTANTIAL UPPER TROUGH TO 
DEVELOP NEAR 35N 175E AND START TO LIFT THE STORM IN A MORE 
NORTHERLY DIRECTION...HOWEVER THE STEERING FLOW WILL WEAKEN DOWN 
AROUND 20N WHERE IOKE SHOULD BE. 06Z GUIDANCE SHIFTS A LITTLE TO 
THE LEFT OR WEST AND SLOWER THAN 00Z APPARENTLY DUE TO SUBTLE 
DIFFERENCES IN HOW THAT UPPER TROUGH WILL EXACTLY FORM. IN THE 48 
TO 120 HOUR RANGE...WE HAVE SLOWED THE SYSTEM SOME ALONG THE LINES 
OF GUIDANCE.

BIGGER QUESTIONS WITH INTENSITY. AS MENTIONED ABOVE...IOKE HAS THE 
POTENTIAL TO DEVELOP QUITE RAPIDLY AND STRONGER THAN WE CURRENTLY 
HAVE. MOST GUIDANCE BRINGS IOKE TO 65 TO 75KT HURRICANE BY 48 HOURS 
AND THEN STEADIES IT OFF AND EVEN SLOWLY DECREASES INTENSITY BY 120 
HOURS. GFDL IS OUTLIER AND BRINGS IOKE TO 95KT AT 96HR TIME FRAME. 
WENT A LITTLE HIGHER ON INTENSITY THAN PREVIOUS FORECAST. CANT 
QUITE UNDERSTAND WHY MOST GUIDANCE WANTS TO START WEAKENING THE 
STORM AFTER 96 HRS GIVEN THAT STILL SHOULD BE IN AREA WITH PRETTY 
WARM SSTS  AND LOW SHEAR. HOWEVER DONT WANT TO DEVIATE TOO MUCH FROM 
PREVIOUS FORECAST. INTENSITY FORECASTS ARE ALWAYS THE HARDEST PART.

ONE IMPORTANT ITEM TO NOTE...BASED ON CURRENT FORECAST...IOKE WILL 
PASS BY ABOUT 75 MILES TO THE SOUTHWEST OF JOHNSTON ISLAND MID DAY 
ON THE 22ND. THIS WOULD PUT THE ISLAND AND THE NATIONAL WILDLIFE 
REFUGE THERE INTO THE 50KT PLUS WINDS THREAT. JOHNSTON IS ALSO 
SUCCEPTIBLE TO HIGH SURF FROM THE SOUTH AND EAST AND IOKE HAS THE 
POTENTIAL TO BRING THAT AS WELL.  INTERESTS IN AND AROUND JOHNSTON 
SHOULD PAY CLOSE ATTENTION TO LATER FORECASTS FROM CPHC.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      20/0900Z 10.6N 159.0W    35 KT
 12HR VT     20/1800Z 11.0N 160.7W    40 KT
 24HR VT     21/0600Z 11.7N 163.3W    50 KT
 36HR VT     21/1800Z 12.8N 166.1W    60 KT
 48HR VT     22/0600Z 13.9N 168.1W    65 KT
 72HR VT     23/0600Z 16.7N 171.3W    70 KT
 96HR VT     24/0600Z 19.3N 173.0W    70 KT
120HR VT     25/0600Z 22.4N 173.6W    65 KT
 
$$
FORECASTER NASH