WTPA41 PHFO 012058
TCDCP1

TROPICAL STORM LANA DISCUSSION NUMBER  10
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP062009
1100 AM HST SAT AUG 01 2009

THE CLOUD PATTERN OF TROPICAL STORM LANA HAS WEAKENED RAPIDLY SINCE 
LATE LAST NIGHT. MOST OF THE ACTIVE CONVECTION HAS DISSIPATED...THE 
HIGHER CLOUD TOPS ARE SHIFTING OFF TO THE NORTH NORTHEAST...AND THE 
LOW LEVEL CENTER IS BECOMING EXPOSED. THESE ARE GOOD INDICATIONS 
THAT SOUTHWEST SHEAR IS WEAKENING THE STORM.

LAST NIGHT LOCATING THE CENTER OF LANA WAS PROBLEMATICAL...BUT A 
SERIES OF MICROWAVE AND VISIBLE SATELLITE IMAGES HAVE ALLOWED US TO 
LOCATE THE CENTER WITH HIGH CONFIDENCE. THESE IMAGES HAVE ALSO GIVEN 
US GOOD CONFIDENCE THAT THE STORM IS BEING SHEARED AS EXPECTED.
 
THE FORECAST TRACK FOLLOWS THE PREVIOUS PACKAGE CLOSELY WITH A 
SLIGHT SHIFT TO THE SOUTH. LANA CONTINUES TO MOVE WESTWARD TO THE 
SOUTH OF A LOW AND MID-LEVEL SUBTROPICAL RIDGE. THE MID LEVEL RIDGE 
IS EXPECTED TO CONTINUE BUILDING WESTWARD IN PHASE WITH LANA OVER 
THE NEXT SEVERAL DAYS...KEEPING THE TROPICAL CYCLONE MOVING ON A 
SLIGHTLY NORTH OF WEST TRACK THROUGH THE FORECAST PERIOD. THE 
FORECAST TRACK IS NEAR THE MIDDLE OF THE ENVELOPE OF THE DYNAMIC 
MODELS. I HAVE SHIFTED THE TRACK SLIGHTLY FURTHER SOUTH SINCE LANA 
IS NOW EXPECTED TO WEAKEN A BIT FASTER. THE FORECAST TRACK HAS LANA 
PASSING OVER 250 MILES SOUTH OF THE MAIN HAWAIIAN ISLANDS TONIGHT 
AND SUNDAY.

OVER THE PAST 24 HOURS LANA HAS BEEN MOVING OVER AN AREA OF SLIGHTLY 
WARMER SEA SURFACE TEMPERATURES...AROUND 27.5C THAT MAY HAVE HELPED 
PRODUCE THE BURST OF CONVECTION LAST EVENING. LANA SHOULD NOW BE 
MOVING OVER SLIGHTLY COOLER WATER FOR THE NEXT 24 HOURS...AROUND 1C 
COOLER. THESE SSTS WOULD STILL BE ADEQUATE TO MAINTAIN THE STORM BUT 
INCREASING VERTICAL SHEAR IS LIKELY TO WEAKEN THE STORM. SINCE THE 
LATEST SATELLITE IMAGERY HAS ALREADY SHOWN LANA BEING DECAPITATED BY 
THE VERTICAL SHEAR WE HAVE FORECAST WEAKENING TO OCCUR A BIT FASTER 
THAN THE PREVIOUS FORECAST.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      01/2100Z 14.5N 153.4W    45 KT
 12HR VT     02/0600Z 14.8N 155.8W    40 KT
 24HR VT     02/1800Z 15.2N 158.9W    35 KT
 36HR VT     03/0600Z 15.7N 161.9W    30 KT
 48HR VT     03/1800Z 15.9N 164.7W    25 KT...DISSIPATING
 72HR VT     04/1800Z 16.4N 169.9W    25 KT...DISSIPATING
 96HR VT     05/1800Z 16.9N 175.3W    20 KT...REMNANT LOW
120HR VT     06/1800Z 17.3N 179.4E    20 KT...REMNANT LOW
 
$$
FORECASTER DONALDSON