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Tropical Storm Rosa Forecast Discussion


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927 
WTPZ45 KNHC 252054
TCDEP5

Tropical Storm Rosa Discussion Number   3
NWS National Hurricane Center Miami FL       EP202018
300 PM MDT Tue Sep 25 2018

Rosa has become better organized this afternoon.  An earlier 1601
UTC GMI microwave image showed impressive banding features in the
south semicircle with a banding eye type feature wrapping three
quarters around the center of circulation.  A blend of the Dvorak
intensity estimates from TAFB and SAB yield an initial intensity of
45 kt for this advisory.

Although there is some modest northeasterly shear impinging in the
northeast side of the cyclone, the SHIPS intensity guidance
indicate that this shear will diminish in 12 hours.  Subsequently,
the SHIPS RI index and the DTOPS model indicate a relatively high
probability of rapid intensification in 24 hours.  Accordingly, the
NHC forecast calls for Rosa to become a hurricane in 12 hours based
on these data.  Further strengthening through the 72 hour period is
expected and is based on the IVCN multi-model intensity consensus.
Beyond day 3, gradual weakening is expected due to increasing shear
and slightly cooler waters.

The initial motion is estimated to be west-northwestward, or 290 at
8 kt, and this general motion is forecast to continue through the
next 3 days south of a mid-level ridge extending from northern
Mexico westward over the eastern Pacific. In response to a
mid-latitude trough approaching from the northwest, Rosa should turn
towards the northwest to north over the weekend.  It is worth noting
that there is considerable along and cross-track spread in the track
guidance beyond day 3.  Therefore, the official track forecast
follows the TVCN consensus, which lies in between the left and right
global model outlier clusters.


FORECAST POSITIONS AND MAX WINDS

INIT  25/2100Z 15.0N 108.9W   45 KT  50 MPH
 12H  26/0600Z 15.4N 110.0W   65 KT  75 MPH
 24H  26/1800Z 15.9N 111.5W   80 KT  90 MPH
 36H  27/0600Z 16.3N 113.1W   95 KT 110 MPH
 48H  27/1800Z 16.5N 114.8W  100 KT 115 MPH
 72H  28/1800Z 17.3N 118.0W  110 KT 125 MPH
 96H  29/1800Z 19.2N 120.0W  100 KT 115 MPH
120H  30/1800Z 21.7N 120.8W   80 KT  90 MPH

$$
Forecaster Ramos/Roberts