553 
 WTPA41 PHFO 011444
 TCDCP1
 
 TROPICAL STORM LANA DISCUSSION NUMBER   9
 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP062009
 500 AM HST SAT AUG 01 2009
 
 PULSING CONVECTION ACROSS THE NORTHERN SEMICIRCLE OF LANA HAS
 ALLOWED THE TROPICAL STORM TO MAINTAIN ITS INTENSITY DESPITE THE
 PRESENCE OF SIGNIFICANT VERTICAL WIND SHEAR. PINPOINTING THE LOW
 LEVEL CENTER REMAINS A CHALLENGE...BUT A 36 GHZ MICROWAVE IMAGE
 JUST IN HAS RAISED THE CONFIDENCE IN THE CENTER POSITION. THE
 INITIAL POSITION IS AT 14.6N 151.0W...CLOSE TO THE PHFO AND SAB
 FIXES WHICH PUT THE CENTER ALONG THE SOUTHEAST EDGE OF A BAND OF
 CONVECTION THAT FLARED OVERNIGHT. THIS POSITION ALSO PROVIDES
 CONTINUITY WITH THE PREVIOUS FORECAST PACKAGE...YIELDING A MOTION
 OF 280/14 KT. INITIAL INTENSITY REMAINS 45 KT IN AGREEMENT WITH THE
 FINAL T NUMBERS FROM PHFO...SAB...AND JTWC AND SLIGHTLY HIGHER THAN
 THE 35 KT SUGGESTED BY CIMSS ADT.
 
 THE FORECAST TRACK FOLLOWS THE PREVIOUS PACKAGE CLOSELY. LANA
 CONTINUES TO MOVE WESTWARD TO THE SOUTH OF A LOW AND
 MID-LEVEL SUBTROPICAL RIDGE...WHILE SOUTHWESTERLY WINDS ALOFT
 CONTINUE TO PROMOTE CONVECTION AND OUTFLOW ACROSS THE NORTHERN
 QUADRANT OF THE SYSTEM. THE MID LEVEL RIDGE IS FORECAST TO BUILD
 WESTWARD IN PHASE WITH LANA OVER THE NEXT SEVERAL DAYS...KEEPING THE
 TROPICAL CYCLONE MOVING GENERALLY TOWARD THE WEST TO WEST-NORTHWEST
 THROUGH THE FORECAST PERIOD. THE FORECAST TRACK IS VERY CLOSE TO
 THE MIDDLE OF THE ENVELOPE OF THE DYNAMIC MODELS AND REMAINS JUST
 NORTH OF THE CONSENSUS. ALONG THIS TRACK...LANA IS EXPECTED TO PASS
 A COUPLE HUNDRED MILES SOUTH OF THE MAIN HAWAIIAN ISLANDS TONIGHT
 AND SUNDAY.
  
 INCREASING VERTICAL WIND SHEAR WILL BE THE MAIN FACTOR IN THE
 INTENSITY FORECAST...SINCE SST VALUES WILL REMAIN AT 27C OR
 GREATER. AN UPPER LEVEL TROUGH CENTERED JUST WEST OF THE
 MAIN HAWAIIAN ISLANDS IS PRODUCING THE WIND SHEAR...WHICH INCREASES
 RAPIDLY TO THE WEST OF THE TROPICAL CYCLONE ACCORDING TO THE LATEST
 CIMSS ANALYSIS. THE UPPER LEVEL TROUGH WILL PINCH OFF AN UPPER LOW
 SOUTHWEST OF THE ISLANDS...WHICH IS FORECAST TO DRIFT WESTWARD OVER
 THE NEXT COUPLE OF DAYS. WITH LANA TRAVELLING WESTWARD FASTER THAN
 THE UPPER LOW...VERTICAL WIND SHEAR IS EXPECTED TO STEADILY
 INCREASE...CAUSING LANA TO WEAKEN. THIS DOWNWARD TREND IN INTENSITY
 IS EXPECTED TO BEGIN TODAY...WITH LANA WEAKENING INTO A TROPICAL
 DEPRESSION BY SUNDAY AND BECOMING A REMNANT LOW AROUND DAY 4. THE
 INTENSITY FORECAST CLOSELY FOLLOWS THE HWRF...WHICH WEAKENS LANA
 SLIGHTLY FASTER THAN THE OTHER ICON CONSTITUENTS.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      01/1500Z 14.7N 151.7W    45 KT
  12HR VT     02/0000Z 15.1N 153.8W    40 KT
  24HR VT     02/1200Z 15.5N 156.7W    35 KT
  36HR VT     03/0000Z 15.9N 159.5W    30 KT
  48HR VT     03/1200Z 16.4N 162.2W    30 KT
  72HR VT     04/1200Z 17.1N 167.7W    25 KT...DISSIPATING
  96HR VT     05/1200Z 17.7N 173.2W    20 KT...REMNANT LOW
 120HR VT     06/1200Z 18.2N 178.6W    20 KT...REMNANT LOW
  
 $$
 FORECASTER WROE/HOUSTON