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NOAA NOAA United States Department of Commerce

Tropical Storm KARINA


800 AM PDT SUN AUG 17 2014

There has been little change to Karina's convective organization
since the previous advisory. A large mass of deep convection with
cloud tops to near -80C remains sheared to the west and southwest
of the partially exposed low-level circulation center due to
moderate easterly vertical wind shear. The intensity was increased
slightly to 40 kt based on ASCAT data that arrived after the
previous advisory had been issued, which showed reliable 38-39 kt
wind vectors to the west of the low-level center.

Karina has been moving due west or 270/10 kt over the past 6 hours.
There is no significant change to previous forecast track or
prognostic reasoning. Karina is expected to gradually make a turn
toward the west-southwest over the next 24 hours, and then
maintain that motion accompanied by a decrease in forward speed
through 72 hours as a large ridge to the north of the Hawaiian
Island builds southward to the west of the cyclone. After that, the
large disturbance located about 700 nmi east of Karina is expected
to develop and become a very large circulation, more than than
twice the normal size of a tropical cyclone. That system is
forecast to dominate the steering flow across much of the eastern
North Pacific, producing a long fetch of low- to mid-level
southwesterly flow that is expected to gradually steer Karina back
toward the east and northeast on Days 4 and 5. It is possible
that Karina could stall on Day 3 when steering currents briefly
collapse. The NHC forecast track is similar to the previous advisory
track and closely follows the consensus model TVCE.

The GFS-based SHIPS intensity guidance shows only 7 kt of easterly
850-200 mb wind shear currently affecting Karina, an analysis that
appears to be too weak given the large westward displacement of the
deep convection. In contrast, UW-CIMSS shear analyses indicate about
15 kt of easterly mid-level shear is affecting the cyclone, which
likely better explains the very asymmetric convective cloud pattern.
The overall shear pattern is not forecast to change much for the
next 5 days, so little change in strength is expected during that
time, especially since Karina will be over or near marginal SSTs of
26-26.5C throughout the forecast period. The official intensity
forecast is just an update of the previous advisory, and closely
follows the ICON intensity consensus model.


INIT  17/1500Z 18.0N 128.2W   40 KT  45 MPH
 12H  18/0000Z 17.6N 129.5W   40 KT  45 MPH
 24H  18/1200Z 16.9N 131.2W   45 KT  50 MPH
 36H  19/0000Z 16.4N 132.4W   45 KT  50 MPH
 48H  19/1200Z 16.2N 133.1W   50 KT  60 MPH
 72H  20/1200Z 16.2N 133.8W   45 KT  50 MPH
 96H  21/1200Z 16.4N 134.1W   45 KT  50 MPH
120H  22/1200Z 16.6N 133.3W   45 KT  50 MPH

Forecaster Stewart