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Tropical Depression Ten-E Discussion Number   1
NWS National Hurricane Center Miami FL       EP102018
200 PM PDT Tue Jul 31 2018

The broad low pressure system and area of disturbed weather that the
NHC has been tracking for the past several days has finally become
well-defined enough and has acquired sufficient organized deep
convection near the center to be classified as a tropical
depression. The low-level center is estimated to be just inside the
southeastern edge of the figure-6 cloud mass based on conventional
and microwave satellite fix data. The initial intensity estimate of
30 kt is based on Dvorak satellite classifications of T2.0/30 kt
from TAFB and T2.5/35 kt from SAB, along with uncontaminated 30-kt
winds in a 1634 UTC Scatsat-1 scatterometer pass.

The initial motion estimate is west-northwestward or 290/11 kt. A
deep-layer ridge to the north of the depression should keep the
tropical cyclone moving toward the west-northwest for the next 48
hours or so, followed by a turn toward the west thereafter due to
the ridge building slightly southward on days 3-5. The NHC track
forecast closely follows a blend of the consensus models TVCN and
HCCA since this is the first forecast on this system.

Although the comma-shaped cloud pattern is suggestive of a slightly
stronger system, microwave imagery and the Scatsat-1 pass indicate
that the circulation envelope is elongated northeast-to-southwest,
and that westerly winds likely only extend about 30 n mi to the
south of the center. Due to the cyclone's irregular shape, the peak
winds are being held lower than the Dvorak T2.5 data-T numbers.
Visible satellite imagery shows the tops of shallow convection in
the eastern semicircle blowing off toward the west, which is
indicative of modest mid-level shear undercutting the favorable
high-level cirrus outflow layer. This mid-level flow is also likely
producing some intrusions of dry air, a negative condition that
should act to inhibit inner-core convective development in the short
term. These aforementioned unfavorable environmental conditions, in
conjunction with the irregular shape of the cyclone's circulation,
should result in only slow strengthening for the next 48 hours or
so, despite the very favorable deep-layer, low vertical wind shear
environment. In the 48-72 h period, both the GFS and ECMWF models
are forecasting the shear to increase to near 15 kt, which should
act to maintain only slow development. By days 4 and 5, the shear is
forecast to abate, and the cyclone is forecast to become a hurricane
by 120 hours. The intensity forecast follows the trend of the HCCA
and IVCN intensity consensus models, but is slightly higher due to
the HMON model showing immediate weakening, which is pulling down
the consensus intensity forecasts.

FORECAST POSITIONS AND MAX WINDS

INIT  31/2100Z 12.7N 116.7W   30 KT  35 MPH
 12H  01/0600Z 13.1N 118.4W   35 KT  40 MPH
 24H  01/1800Z 13.6N 120.3W   40 KT  45 MPH
 36H  02/0600Z 13.8N 122.4W   45 KT  50 MPH
 48H  02/1800Z 14.0N 124.6W   50 KT  60 MPH
 72H  03/1800Z 13.8N 128.7W   55 KT  65 MPH
 96H  04/1800Z 13.7N 132.6W   60 KT  70 MPH
120H  05/1800Z 13.6N 136.7W   65 KT  75 MPH

$$
Forecaster Stewart

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