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Tropical Storm ALETTA


Tropical Storm Aletta Discussion Number   7
NWS National Hurricane Center Miami FL       EP022018
900 AM MDT Thu Jun 07 2018

The low-level center of Aletta has been somewhat difficult to locate
this morning.  Moderate westerly shear still appears to be affecting
the tropical storm, and a recent SSMIS pass at 1329 UTC indicates
that the low-level center is displaced slightly to the west of the
mid-level center.  A pronounced dry slot is present in IR and WV
imagery, though a recent burst of convection near the center
suggests that it may no longer be substantially inhibiting
convection.  Subjective Dvorak intensity estimates from TAFB and SAB
at 1200 UTC were 55 kt, while objective estimates from SATCON and
the ADT are around 60 kt.  Given the increase of convection near the
center since the TAFB and SAB classifications, the initial intensity
has been raised to 60 kt.

Little change has been made to the intensity forecast, which is
slightly above the consensus guidance IVCN and HCCA, but below a
mean of the dynamical hurricane models.  The westerly shear
currently affecting Aletta is expected to decrease over the next 12
to 24 hours, allowing the tropical storm to strengthen. By 48 hours,
increasing shear and decreasing SSTs will likely induce a weakening
trend that should accelerate through 72 h.  Aletta will likely
become a remnant low sometime near or just after 120 h.

Aletta appears to have taken a slight turn toward the northwest this
morning but the longer-term motion estimate is 290 at about 5 kt.
Aletta will be steered generally west-northwest to northwestward
over the next 5 days, with the largest source of uncertainty being
how deep the circulation will be.  A stronger, deeper cyclone will
likely track farther north in response to an upper-level trough to
the northwest, as shown by the GFS.  A weaker cyclone will instead
be steered more by the mid-level ridge to the north, and move on a
heading closer to due west, as shown by the ECMWF.  The NHC forecast
splits these solutions, and is consistent with the intensity
forecast which also is also lower than the GFS but well above the


INIT  07/1500Z 14.9N 109.3W   60 KT  70 MPH
 12H  08/0000Z 15.1N 110.1W   65 KT  75 MPH
 24H  08/1200Z 15.4N 111.0W   70 KT  80 MPH
 36H  09/0000Z 15.8N 112.0W   75 KT  85 MPH
 48H  09/1200Z 16.4N 112.7W   75 KT  85 MPH
 72H  10/1200Z 17.6N 114.2W   60 KT  70 MPH
 96H  11/1200Z 18.5N 116.0W   40 KT  45 MPH
120H  12/1200Z 18.5N 117.5W   30 KT  35 MPH

Forecaster Zelinsky