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