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Tropical Storm Kristy Discussion Number   5
NWS National Hurricane Center Miami FL       EP132018
800 PM PDT Tue Aug 07 2018

Kristy has become a little less organized this evening.  An upper
tropospheric low situated to the northeast of Kristy is
producing moderate northwesterly shear which has degraded the
cyclone's cloud pattern.  A 2035 UTC AMSR2 overpass revealed that
the surface center was partially exposed to the north of the
convective banding features.  The subjective Dvorak intensity
estimates from TAFB and SAB have decreased as well, so the initial
intensity for this advisory is lowered to 40 kt.

Statistical and global models all show the upper low to the
northeast of Kristy weakening and lifting out in 24 hours or so,
which should provide a more conducive upper wind environment for
intensification, at least through mid-period.  Afterwards, a
weakening trend should commence due to an intruding drier/stable air
mass and cooler oceanic sea surface temperatures.  The HWRF and HCCA
show Kristy becoming a hurricane in 48 hours, which still seems
quite reasonable and is reflected in the forecast.  All of the other
guidance reaches just below 65 kt.  The NHC intensity forecast is
based primarily on these two models, and indicates a peak
intensity of 65 kt in 48 hours.

The initial motion is estimated to be 285/7 kt, and Kristy is being
steered by a narrow mid-level ridge to the northeast.  A complex
synoptic steering pattern comprised of an approaching deep-layer low
pressure system to the northwest of the tropical storm, and John to
the northeast, is forecast by most of the global and regional models
to weaken what's left of the ridge currently steering Kristy.  The
increasing weakness in the subtropical ridge should cause Kristy
to turn northwestward and northward through day 4.  At the end of
the period, a gradual turn toward the northwest around the
periphery of larger John's circulation.  The ECMWF deterministic and
ensemble models continue to be outliers in the aforementioned
scenario due to less influence from the growing weakness to the
north and significantly less binary interaction with John.  The
official forecast is similar to the previous one, with a slight
adjustment to the right and is basically in the middle of the HCCA
and TVCE consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  08/0300Z 14.2N 127.8W   45 KT  50 MPH
 12H  08/1200Z 14.6N 128.7W   45 KT  50 MPH
 24H  09/0000Z 15.4N 129.6W   50 KT  60 MPH
 36H  09/1200Z 16.4N 130.0W   60 KT  70 MPH
 48H  10/0000Z 17.2N 130.1W   65 KT  75 MPH
 72H  11/0000Z 19.5N 129.9W   60 KT  70 MPH
 96H  12/0000Z 22.0N 130.6W   50 KT  60 MPH
120H  13/0000Z 24.3N 133.0W   30 KT  35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Roberts

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