WTPA41 PHFO 020248
TCDCP1

TROPICAL STORM LANA DISCUSSION NUMBER  11
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP062009
500 PM HST SAT AUG 01 2009

CONVECTION AROUND LANA CONTINUES TO PULSE. AT 1000 AM HST...NEARLY 
ALL OF THE CONVECTION AROUND LANA HAD DISSIPATED BUT MORE CONVECTION 
HAS NOW DEVELOPED NORTH OF THE CENTER. THE LOW LEVEL CIRCULATION 
CENTER REMAINS MOSTLY EXPOSED SO WE STILL HAVE HIGH CONFIDENCE IN 
THE CENTER LOCATION. THE PRESENCE OF THE EXPOSED LOW LEVEL CENTER 
AND THE SMALL AMOUNT OF DEEP CONVECTION NEAR THE CENTER ARE 
INDICATIONS THAT LANA IS STRUGGLING TO SURVIVE.
 
THE FORECAST TRACK FOLLOWS THE PREVIOUS PACKAGE CLOSELY WITH A VERY 
SLIGHT SHIFT TO THE SOUTH. LANA CONTINUES TO MOVE WESTWARD TO THE 
SOUTH OF A LOW TO MID-LEVEL SUBTROPICAL RIDGE. THE MID LEVEL RIDGE 
IS EXPECTED TO BUILD WEST SOUTHWEST OVER THE NEXT SEVERAL 
DAYS...KEEPING THE TROPICAL CYCLONE MOVING ON A SLIGHTLY NORTH OF 
WEST TRACK THROUGH THE FORECAST PERIOD. LANA HAS BEEN TRACKING ALONG 
THE SOUTH SIDE OF THE ENVELOPE OF THE DYNAMIC MODELS. I HAVE KEPT 
THE TRACK NEARLY THE SAME...WITH JUST A SLIGHT SHIFT FARTHER SOUTH 
OF THE PREVIOUS TRACK. THE FORECAST TRACK HAS LANA PASSING ABOUT 300 
MILES SOUTH OF SOUTH POINT...THE SOUTHERNMOST POINT IN THE HAWAIIAN 
ISLANDS...AROUND 800 PM TONIGHT.

AS USUAL...THE INTENSITY FORECAST IS MUCH LESS STRAIGHTFORWARD THAN 
THE TRACK FORECAST. OVER THE PAST 24 HOURS LANA HAS BEEN MOVING OVER 
AN AREA OF SLIGHTLY WARMER SEA SURFACE TEMPERATURES...AROUND 
27.5C...AND HIGHER OCEAN HEAT CONTENT...THAT MAY BE HELPING LANA 
SURVIVE. LANA SHOULD NOW START MOVING OVER SLIGHTLY COOLER WATER FOR 
THE NEXT 24 HOURS. THESE SSTS WOULD STILL BE ADEQUATE TO MAINTAIN 
THE STORM IF THE ENVIRONMENT WAS OTHERWISE FAVORABLE.SO PROBABLY THE 
MAIN FACTOR THAT WILL DETERMINE LANAS INTENSITY WILL BE VERTICAL 
SHEAR.

THERE IS A NORTHEAST TO SOUTHWEST TROUGH ALOFT JUST NORTHWEST OF 
KAUAI. SOUTHWEST WINDS ON THE SOUTHEAST SIDE OF THIS TROUGH ARE 
PRODUCING STRONG VERTICAL SHEAR. LANA IS JUST ON THE EDGE OF THIS 
STRONG SHEAR. AS LANA MOVES WEST OVER THE NEXT FEW DAYS...THE TROUGH 
ALOFT AND THE SHEAR ZONE WILL ALSO MOVE WEST. I EXPECT THE SHEAR 
WILL BE STRONG ENOUGH TO KILL LANA OVER THE NEXT 96 HOURS OR 
SO...BUT IT IS NOT A SURE THING. LANA WILL START MOVING OVER WARMER 
WATER AGAIN WEST OF 160W AND THAT COULD GIVE THE CYCLONE A NEW LEASE 
ON LIFE.
 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      02/0300Z 14.5N 155.2W    45 KT
 12HR VT     02/1200Z 14.8N 157.6W    40 KT
 24HR VT     03/0000Z 15.2N 160.6W    35 KT
 36HR VT     03/1200Z 15.5N 163.4W    35 KT
 48HR VT     04/0000Z 15.8N 166.2W    30 KT
 72HR VT     05/0000Z 16.3N 171.4W    25 KT...DISSIPATING
 96HR VT     06/0000Z 16.7N 176.7W    20 KT...REMNANT LOW
120HR VT     07/0000Z 17.0N 178.0E    20 KT...REMNANT LOW
 
$$
FORECASTER DONALDSON