TROPICAL DEPRESSION EIGHT-E DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL EP082015
200 PM PDT MON JUL 27 2015
The low pressure system located more than 1000 n mi west-southwest
of the Baja California peninsula has finally acquired enough
persistent deep convection near the center for it to be upgraded to
a tropical depression. An 1831 UTC ASCAT-B overpass indicated a
well-defined circulation center and inner-core wind field containing
several 30-31 kt surface wind vectors at a distance of 35-40 nmi to
the northeast and southeast of the center. Although the depression
is a sheared tropical cyclone, a T2.0/30 kt Dvorak satellite
classification from TAFB also justifies upgrading the low to a
tropical depression at this time.
The initial motion estimate is 290/14 kt, which is based primarily
on microwave and ASCAT satellite fixes. The NHC model guidance is
in good agreement on the tropical cyclone moving toward the
west-northwest at 12-14 kt for the next 72 hours or so due to a
strong deep-layer ridge locate to its north. After that, however,
the guidance diverges significantly with the ECMWF model taking a
very weak cyclone or trough west-southwestward, the GFS and HWRF
models moving the system westward, while the GFS-ensemble mean and
the remainder of the models keep the depression on a slower
west-northwestward track. The NHC official forecast track basically
lies down the middle of the guidance suite throughout the forecast
period and is close to the consensus model TVCE.
The cyclone is not expected to intensify much due to persistent
moderate northwesterly vertical wind shear and the cyclone moving
over marginal sea-surface temperatures after 72 hours. There will
also likely be occasional intrusions of drier and more stable air,
which lies just to the north of the forecast track, into the
cyclone. However, the well-established southerly low-level inflow
of unstable air should help to maintain enough convection to keep
this system as a tropical cyclone throughout the forecast period.
The NHC intensity forecast is similar to the ICON consensus model.
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