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Hurricane Rosa Discussion Number  13
NWS National Hurricane Center Miami FL       EP202018
200 AM PDT Fri Sep 28 2018

Although enhanced BD-curve infrared imagery shows that Rosa's 20 n
mi wide eye has continued to warm (+16C) this morning, the southwest
quadrant of the eyewall appears to have weakened, or collapsed, and
the inner ring cloud tops have warmed considerably.  This change in
the cloud pattern maybe the early stage of an eyewall replacement
cycle (ERC).  It's certainly worth noting, however, that the
satellite presentation about 3 hours ago indicated that Rosa may
have reached a peak intensity of 130-135 kt which was also
indicated in the ADT adjusted raw T-numbers.  For this advisory,
the initial intensity is set at 125 kt and is based on a compromise
of the subjective and objective satellite intensity estimates.

Rosa has a small window of opportunity to complete its ERC and
restrengthen before it encounters decreasing oceanic temperatures,
and increasing southwesterly shear.  These inhibiting factors, along
with Rosa moving into a more stable air mass, should cause a
downward intensity trend by early next week, and for the cyclone to
weaken to a tropical storm by Tuesday, and a tropical depression as
it quickly moves northeastward over the southwestern U.S.  The
intensity forecast is similar to my predecessor's and is close to
the IVCN consensus through 48 hours, then quite similar to the
NOAA-HCCA intensity model beyond that forecast period.

The initial motion is estimated to be westward, or 270/6 kt.  A
mid-level ridge over the southwestern United States is forecast to
weaken over the next couple of days in response to an approaching
mid-level shortwave trough from the northwest.  This growing
weakness in the ridge should influence Rosa to gradually turn
northward through mid-period, and afterward, turn northeastward
within the strong mid- to upper tropospheric southwesterly flow
produced by the aforementioned trough.  The NHC track forecast was
adjusted ever so slightly to the left of the previous one to light
more closely to the TVCN and HCCA multi-model guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  28/0900Z 16.9N 117.3W  125 KT 145 MPH
 12H  28/1800Z 17.4N 117.9W  130 KT 150 MPH
 24H  29/0600Z 18.4N 118.4W  120 KT 140 MPH
 36H  29/1800Z 20.1N 118.8W  100 KT 115 MPH
 48H  30/0600Z 22.0N 118.8W   85 KT 100 MPH
 72H  01/0600Z 25.9N 117.6W   65 KT  75 MPH
 96H  02/0600Z 30.6N 115.0W   40 KT  45 MPH...INLAND
120H  03/0600Z 38.2N 109.4W   25 KT  30 MPH...POST-TROP/INLAND

$$
Forecaster Roberts

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