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Tropical Depression FOUR-E


ZCZC MIATCDEP4 ALL
TTAA00 KNHC DDHHMM

Tropical Depression Four-E Discussion Number   1
NWS National Hurricane Center Miami FL       EP042018
400 PM CDT Thu Jun 14 2018

Overnight scatterometer data indicate that the circulation of the
system was open on the northwestern side.  High-resolution GOES-16
1-min visible data indicate that the low is now closed, with a
well-enough defined circulation center.  Since there is plenty of
banded convection, this system is being designated as a tropical
depression, and the initial wind speed of 30 kt is based off the
overnight scatterometer data.

The initial motion estimate is an uncertain 325/5 kt.  A weak
mid-level ridge over Mexico is forecast to break down by tomorrow,
leaving the depression in an area of light steering currents.  Much
of the model guidance linger the system just south of the coast of
Mexico for the next couple of days until the cyclone gets drawn
northward into a larger trough currently seen over the western Gulf
of Mexico.  There is considerable uncertainty in the timing of this
poleward motion, however, with the UKMET, HMON, and COAMPS-TC models
faster than the rest of the guidance.  This seems like a pretty
clear case of staying near the model consensus, given the weak
steering flow that makes it nearly impossible to choose one model
over another one.  Thus, the official forecast shows a slow
northward motion, near the eastern Pacific model consensus TVCE, and
it should be emphasized that the forecast timing of landfall is
subject to large changes in the future.

The system is not particularly well organized at the moment, with a
few swirls seen in the visible imagery rotating around the larger
gyre.  After the low consolidates, light-to-moderate shear with
very warm waters, and high mid-level humidity should lead to steady
intensification.  This is a tricky forecast, however, since land is
so close to the north, which would prevent much strengthening.  The
official forecast is a blend of the statistical-dynamical guidance
and the regional hurricane guidance, a bit lower than the model
consensus since the HWRF keeps the cyclone well offshore (unlike
the official prediction), leading to a stronger storm.

It has been an active early part of the eastern Pacific season.
This is the 2nd earliest 4th tropical cyclone on record in the
basin during the satellite era (1966-present), only 6 hours behind
the previous record in 1974.

FORECAST POSITIONS AND MAX WINDS

INIT  14/2100Z 15.5N 100.1W   30 KT  35 MPH
 12H  15/0600Z 16.1N 100.5W   30 KT  35 MPH
 24H  15/1800Z 16.3N 100.6W   35 KT  40 MPH
 36H  16/0600Z 16.5N 100.5W   40 KT  45 MPH
 48H  16/1800Z 16.7N 100.3W   50 KT  60 MPH
 72H  17/1800Z 17.1N 100.3W   40 KT  45 MPH...INLAND
 96H  18/1800Z 17.5N 100.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  19/1800Z...DISSIPATED

$$
Forecaster Blake

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