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TROPICAL STORM LESTER DISCUSSION NUMBER  54
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP132016
500 PM HST TUE SEP 06 2016
 
Lester's satellite presentation has degraded somewhat over the
past 6 to 12 hours, and the system has the appearance of a
sheared tropical cyclone, with limited convection confined to the
southeast semicircle. The low-level center has been exposed since
this morning, with northwesterly shear provided by a nearby low
aloft at least partially responsible for the current structure.
This may be the anticipated beginning of the transition to an
extratropical cyclone. While latest subjective Dvorak intensity
estimates indicate that Lester is below tropical storm intensity, a
pair of late-morning ASCAT passes indicated otherwise. The passes at
2033Z and 2126Z were critical in determining the initial intensity
of 45 kt for this package, with a nearly 70 nm wide swath of 35-40+
kt winds sampled in the eastern semicircle. 

Lester is tracking toward the north between a deep-layer ridge to
the east, and an approaching mid-latitude trough to the northwest,
and the initial motion estimate for this advisory is 010/11 kt. The
official track forecast is essentially an update of the previous, as
the forecast philosophy and track guidance remain consistent. Lester
will make a turn toward the northeast over the next 12 to 24 hours
as it rounds the western periphery of the ridge, and forward speed
is expected to increase dramatically as it becomes embedded in an
increasingly deep southwesterly flow. The official track forecast is
aided by guidance from the Ocean Prediction Center (OPC), and is
primarily based on a blend of the global models GFS, ECMWF and
UKMET. 

Also based on OPC and global model guidance, the transition to an
extratropical low is expected to be complete in about 24 hours. 
Although the wind field will be undergoing some changes as this
occurs, little change in intensity is expected. Lester's existence
as an extratropical low is expected to be brief, as it is forecast
to dissipate on Thursday as it gets caught up in the circulation of
a larger extratropical low near the Gulf of Alaska.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  07/0300Z 35.1N 166.2W   45 KT  50 MPH
 12H  07/1200Z 37.0N 165.5W   45 KT  50 MPH
 24H  08/0000Z 40.4N 163.1W   50 KT  60 MPH...POST-TROP/EXTRATROP
 36H  08/1200Z 45.0N 158.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 48H  09/0000Z...POST-TROP/EXTRATROP
 
$$
Forecaster Birchard
 
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