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Tropical Storm EUGENE


Tropical Storm Eugene Discussion Number   3
NWS National Hurricane Center Miami FL       EP052017
300 AM MDT Sat Jul 08 2017

Eugene's convective pattern has continued to improve since the
previous advisory, with a pronounced band of cold-topped convection
now wrapping more than halfway around the center. An ASCAT-A pass
at 0432Z indicated peak winds of 37 kt north of the center, but the
northeastern quadrant was missed where stronger winds could be
occurring. The initial intensity is being maintained at 40 kt for
this advisory based on consensus T2.5/35 estimates from TAFB and
SAB, and a UW-CIMSS ADT estimate of T2.7/39 kt.

The initial motion remains 315/08 kt. There is no significant change
to previous forecast track or reasoning. Eugene is expected to
continue moving around the southwestern periphery of a deep-layer
ridge that extends westward across central and northern Mexico for
the next 36-48 hours, and afterwards move into a weakness that is is
forecast to develop in the ridge well to the west of the Baja
California peninsula. The latest NHC model guidance is tightly
packed about the previous forecast track, so only minor along-track
speed changes were required.

The aforementioned ASCAT pass indicates that the inner-core wind
field of Eugene has become better defined and that the radius of
maximum winds has also contracted down to about 30 n mi. As
mentioned in the previous discussion, this now smaller RMW, in
conjunction with a nearly ideal environment, would typically support
rapid intensification. However, AMSU microwave and new GOES-16 water
vapor imagery indicate that a pronounced tongue of dry air has
penetrated into the southwestern quadrant, temporarily disrupting
the development of inner-core convection. But should the dry air mix
out during the next 12 h or so, then rapid strengthening is still a
distinct possibility before Eugene reaches colder water shortly
after the 36-h period. Beyond that time, the cyclone will be moving
over muh colder SSTs ranging from 21-24 deg C, which should induce
rapid weakening despite the low vertical wind shear conditions that
will exist throughout the forecast period. The new intensity
forecast is similar to the previous advisory, and closely follows
the HCCA consensus model.


INIT  08/0900Z 12.9N 112.1W   40 KT  45 MPH
 12H  08/1800Z 13.7N 113.0W   50 KT  60 MPH
 24H  09/0600Z 14.9N 114.1W   60 KT  70 MPH
 36H  09/1800Z 16.4N 115.2W   70 KT  80 MPH
 48H  10/0600Z 17.9N 116.5W   70 KT  80 MPH
 72H  11/0600Z 20.5N 119.0W   55 KT  65 MPH
 96H  12/0600Z 22.9N 121.2W   40 KT  45 MPH...POST-TROPICAL
120H  13/0600Z 25.1N 123.3W   25 KT  30 MPH...POST-TROP/REMNT LOW

Forecaster Stewart