Tropical Storm Cosme Discussion Number 1
NWS National Hurricane Center Miami FL EP032019
800 AM PDT Sat Jul 06 2019
The broad area of low pressure that we have been monitoring for
several days has finally consolidated into a tropical storm.
Satellite images show that a well-defined center is present on the
western side of an area of deep convection which has been
getting closer to the center. The initial wind speed is set to 45
kt in agreement with the overnight scatterometer data, which is
higher than what Dvorak-only estimates would suggest.
Shear near Cosme has been decreasing during the overnight hours,
with cirrus cloud motions suggesting that easterly flow is
overspreading the circulation. However, it will take some time for
the large cyclone to overcome the very dry mid-level air near and
west of the core. In addition, Cosme has only about 36 hours over
lukewarm SSTs before reaching cool waters. These factors suggest
little significant strengthening this weekend, and a gradual
weakening early next week due to sub-26C waters and higher shear.
Only the HWRF shows any significant increase in wind speed, with the
rest of the models holding Cosme's intensity flat or decreasing
during the next few days. The official intensity forecast goes with
the latter solution, not too far from the model consensus.
An uncertain estimate of initial motion is 290/12. Cosme should
be steered to the west-northwest for the next day or so due to a
subtropical ridge over Mexico. However all of the models show a
break in the ridge forming between 120-130W, which will likely
induce a motion more to the northwest by Monday. There isn't a lot
of agreement, however, on exactly when that turns occurs, with the
GFS-based guidance and UKMET turning the system the system earlier
than the ECMWF and most of its ensemble. I don't have a lot of
reason to favor either solution at this time, so the forecast will
stay close to the eastern Pacific track model consensus TVCE. Based
on SSTs and model-simulated satellite data, Cosme should become a
non-convective remnant low in about 3 days.
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