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Tropical Storm JOHN


Tropical Storm John Discussion Number   2
NWS National Hurricane Center Miami FL       EP122018
900 PM MDT Sun Aug 05 2018

Convection associated with Tropical Depression Twelve-E has
continued to become better organized, although recent microwave
satellite data suggest the low-level center is elongated from
northwest to southeast.  Satellite intensity estimates from TAFB and
SAB have increased to 35 kt, and based on these the depression is
upgraded to Tropical Storm John.

The initial motion is 315/7.  A westward-moving mid- to upper-level
trough over northern Mexico has weakened the subtropical ridge over
the northeastern Pacific, and the large-scale models are in good
agreement that John will move northwestward at an increasing
forward speed toward this weakness.  A complicating factor is that
John may interact with Tropical Storm Ileana to the east.  However,
John is much larger than Ileana, and the most likely impact of this
interaction is that John could move a little slower than currently
forecast.  The new forecast track is a little to the north of the
previous track after 48 h, but is otherwise similar to the previous
forecast.  The new track also lies just south of the cluster of
consensus models.

John is expected to be in an environment of very warm SSTs, low
shear, and a moist atmosphere through about 60 h.  This environment
is quite favorable for rapid intensification (RI), as indicated by
high probabilities in the SHIPS RI index, and it is likely that RI
will begin as soon as the inner core of the storm becomes better
organized.  The NHC forecast calls for the storm to become a
hurricane in 24-36 h and to reach a peak intensity of 95 kt in about
three days.  After that, the forecast track takes John over rapidly
cooling sea surface temperatures, which should cause at least a
steady weakening.  The intensity forecast is in best agreement with
the intensity consensus.  It should be noted, however, that the
SHIPS and LGEM models both show more intensification than the
official forecast and make John a major hurricane in about three


INIT  06/0300Z 14.9N 106.2W   35 KT  40 MPH
 12H  06/1200Z 15.6N 107.0W   45 KT  50 MPH
 24H  07/0000Z 16.3N 107.9W   60 KT  70 MPH
 36H  07/1200Z 17.3N 108.9W   75 KT  85 MPH
 48H  08/0000Z 18.5N 110.3W   90 KT 105 MPH
 72H  09/0000Z 21.5N 113.5W   95 KT 110 MPH
 96H  10/0000Z 24.0N 118.0W   65 KT  75 MPH
120H  11/0000Z 26.0N 122.0W   40 KT  45 MPH

Forecaster Beven