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Tropical Storm John Discussion Number  17
NWS National Hurricane Center Miami FL       EP122018
200 PM PDT Thu Aug 09 2018

John has resumed its gradual weakening.  Cloud tops near the center
of the tropical storm have warmed, and several recent microwave
overpasses indicate that deep convection is still primarily limited
to the northern and western semicircles. The intensity has been
lowered to 55 kt based on a the latest Dvorak CI estimates from TAFB
and SAB, and it is possible this is generous. No change has been
made to the intensity forecast, and continued steady weakening
should continue for the next day or two. The most recent dynamical
guidance indicates that John is likely to become a remnant low
around 36 h, so the forecast conservatively shows the system
maintaining tropical cyclone status through that time. Once it
becomes a remnant low, the cyclone will gradually spin down until
dissipating early next week.

The tropical storm has made a left-of-track jog over the past few
hours, and the initial motion estimate is now 290/13 kt.  Due to
this shift, the track forecast has been adjusted west and south
through the entire forecast period. That said, there has been no
other significant change to the forecast reasoning or track
guidance. The cyclone should continue moving west-northwestward
around a mid-level ridge centered over the southwestern U.S. for the
next day or two.  After becoming post-tropical, the remnant
circulation of John is forecast to begin drifting slowly within an
area of weak low-level steering flow. The new NHC forecast is very
close to the multi-model consensus TVCN throughout the forecast
period.

Large swells associated with John are already affecting portions of
the coast of the Baja California peninsula and are forecast to
spread northward and reach portions of the southern California coast
by tonight. These swells are likely to cause life- threatening surf
and rip current conditions. Please consult products from your local
weather office.

FORECAST POSITIONS AND MAX WINDS

INIT  09/2100Z 24.8N 118.5W   55 KT  65 MPH
 12H  10/0600Z 25.5N 120.2W   45 KT  50 MPH
 24H  10/1800Z 26.4N 122.0W   35 KT  40 MPH
 36H  11/0600Z 27.1N 123.4W   35 KT  40 MPH
 48H  11/1800Z 27.7N 124.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  12/1800Z 28.5N 125.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  13/1800Z 29.0N 126.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  14/1800Z...DISSIPATED

$$
Forecaster Zelinsky

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