Tropical Depression TWENTY-TWO-E (Text)


Tropical Depression Twenty-Two-E Discussion Number   3
NWS National Hurricane Center Miami FL       EP222018
1000 PM CDT Sun Oct 14 2018

For the first time in the depression's (and its predecessor low's)
existence, deep convection has persisted for more than a few hours.
The convective canopy has been slowly expanding, although it is
still a little restricted on the eastern side due some easterly
shear.  Based on microwave data, the structure of the cyclone has
been slow to improve in organization, and consensus T2.0s from TAFB
and SAB support maintaining a 30-kt initial intensity.

The depression is located near the western edge of a mid-level
ridge, with a deep-layer trough located not too far to the north
across northwestern Mexico and the western United States.  Its
position places the depression within weak steering currents, and
the system is likely to drift west-northwestward or even meander at
speeds of less than 5 kt for much of the forecast period.  The track
guidance has shifted a little more to the northwest on this cycle,
and the NHC forecast has therefore been adjusted north of the
previous official forecast, although not as far as the TVCN
multi-model consensus nor the HCCA aid.  Despite this adjustment,
the cyclone is expected to remain small, which should keep
tropical-storm-force winds offshore of the coast of Mexico.

The forecast reasoning for the future intensity has changed
substantially.  For the first 3 days, vertical shear is expected to
gradually decrease, and the cyclone's small size will make it prone
to significant strengthening during that period.  In fact, based on
the Rapid Intensification Indices, the chance of a 30-kt increase
in 24 hours is 3 times more than average, and the chance of a 65-kt
increase in 72 hours is almost 9 times more than average.
Therefore, the NHC intensity forecast is above most of the guidance
through day 3, with the possibility of the depression becoming a
hurricane during that time.  After day 3, the models are trending
toward the cyclone entering a region of higher shear associated
with the western U.S. trough, which would likely lead to a
weakening trend.  Most of the intensity models suggest that the
cyclone's intensity will peak around 3 days, and therefore the NHC
intensity forecast now indicates weakening on days 4 and 5
(although it is still well above most of the models).  This is a
low-confidence intensity forecast, and additional adjustments are
likely in future advisories.

The small size of the circulation and its projected motion away from
Mexico does not require tropical storm warnings or watches at this
time. However, only a slight deviation to the right of the forecast
track would bring stronger winds closer to the coast, which would
require the issuance of a tropical storm warning. Regardless of the
winds, heavy rainfall will be the primary threat along the coast of
southwestern Mexico due to the system's slow motion, and flash
flooding will be possible in mountainous areas.


INIT  15/0300Z 17.5N 104.3W   30 KT  35 MPH
 12H  15/1200Z 17.7N 104.7W   35 KT  40 MPH
 24H  16/0000Z 17.7N 104.7W   40 KT  45 MPH
 36H  16/1200Z 17.8N 105.0W   45 KT  50 MPH
 48H  17/0000Z 17.9N 105.3W   50 KT  60 MPH
 72H  18/0000Z 18.4N 106.8W   65 KT  75 MPH
 96H  19/0000Z 19.3N 108.4W   60 KT  70 MPH
120H  20/0000Z 19.6N 108.9W   55 KT  65 MPH

Forecaster Berg


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Page last modified: Monday, 31-Dec-2018 12:11:28 UTC