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Tropical Storm John Discussion Number   3
NWS National Hurricane Center Miami FL       EP122018
300 AM MDT Mon Aug 06 2018

The convective pattern of John has become significantly better
organized during the past several hours, with a large central dense
overcast forming and cloud top temperatures to -85C.  A 0706Z GPM
microwave pass shows the rapid development of an inner core since
the previous pass 6 hours ago, along with impressive curved banding
features.  A blend of the satellite intensity estimates gave 45 kt
at 0600 UTC, but given the increase in organization since that time,
the advisory wind speed is set to 50 kt.

All systems are go for the rapid intensification of John in an
environment of very warm SSTs, high mid-level moisture and low wind
shear.  With the inner core formation, John will likely strengthen
quickly until it reaches cooler waters after 48 hours. The various
rapid intensification aids are about as high as they get, roughly 60
to 90 percent depending on the threshold, increasing the confidence
in the forecast.   Thus the new NHC wind speed prediction is raised
from the previous one, and calls for rapid intensification through
48 hours.  It should be noted that even though the NHC forecast is
rather bullish, the corrected consensus aids, the SHIPS and LGEM
models all show an even higher peak intensity.

The GPM pass helped set the initial motion at 300/7 kt, somewhat to
the left of the previous estimate.  Model guidance remains in fairly
good agreement that John should move northwestward soon at an
increasing forward speed toward a weakness in the subtropical ridge.
While some interaction with TS Ileana is anticipated, the much
larger John should dominate, leading to perhaps a temporary
slowdown.  The latest NHC forecast is shifted to the west in the
first couple of days, following the trend of the model guidance, but
ends up very close to the previous forecast at day 5.  The UKMET is
significantly farther west, perhaps due to it having the two
tropical cyclones analyzed with nearly the same size, and little
weight is placed on that model for the official forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  06/0900Z 15.1N 107.3W   50 KT  60 MPH
 12H  06/1800Z 15.6N 108.1W   65 KT  75 MPH
 24H  07/0600Z 16.3N 109.0W   80 KT  90 MPH
 36H  07/1800Z 17.5N 110.2W   95 KT 110 MPH
 48H  08/0600Z 18.8N 111.7W  110 KT 125 MPH
 72H  09/0600Z 21.8N 115.3W   95 KT 110 MPH
 96H  10/0600Z 24.5N 119.5W   65 KT  75 MPH
120H  11/0600Z 26.5N 124.0W   40 KT  45 MPH...POST-TROPICAL

$$
Forecaster Blake

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