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Hurricane Rosa Discussion Number  12
NWS National Hurricane Center Miami FL       EP202018
800 PM PDT Thu Sep 27 2018

Rosa has continued to rapidly intensify during the past several
hours, with a distinct and warm eye noted on satellite images along
with deep eyewall convection.  A blend of the latest Dvorak
estimates gives an initial wind speed estimate of 125 kt, making
Rosa the seventh category 4 hurricane of the very busy 2018 eastern
Pacific hurricane season.  It is worth noting that this value ties
2015 for the highest observed seasonal total in the basin during
the satellite era.

The hurricane still has a chance to intensify further given that it
is still over warm waters within light shear.  By the weekend,
however, Rosa will encounter more marginal SSTs, and the shear
will likely increase.  These conditions should cause a significant
weakening of the hurricane by early next week, and for Rosa to fall
back to a tropical storm by Tuesday.  The intensity forecast isn't
particularly confident at long range because of the possibility of a
trough interaction somewhat offsetting the effects of cool eastern
Pacific waters and dry stable air.  So far the guidance is fairly
consistent, and the forecast continues to show steady weakening as
Rosa approaches Baja California.

Rosa continues moving at 265 deg, now at 8 kt.   A mid-level ridge
over the southwestern United States is forecast to weaken and move
eastward over the next couple of days as a mean mid-tropospheric
trough forms near the west coast of the US.  This synoptic pattern
should cause the tropical cyclone to gradually turn northward over
that time, and eventually move to the northeast due to Rosa getting
caught up into southwestern flow ahead of the trough.  While there
are still some notable speed differences in the model guidance, the
overall trend is for a faster solution, which is consistent with a
more vertically deep system feeling the stronger mid-level flow.
The model consensus continues the faster trend, and the new
forecast follows suit.


FORECAST POSITIONS AND MAX WINDS

INIT  28/0300Z 16.9N 116.7W  125 KT 145 MPH
 12H  28/1200Z 17.1N 117.7W  130 KT 150 MPH
 24H  29/0000Z 17.8N 118.4W  125 KT 145 MPH
 36H  29/1200Z 19.0N 118.8W  115 KT 130 MPH
 48H  30/0000Z 20.9N 118.8W  100 KT 115 MPH
 72H  01/0000Z 25.0N 118.0W   75 KT  85 MPH
 96H  02/0000Z 29.0N 115.5W   45 KT  50 MPH
120H  03/0000Z 36.0N 110.5W   25 KT  30 MPH...POST-TROP/INLAND

$$
Forecaster Blake

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