Tropical Storm Lowell Discussion Number 5
NWS National Hurricane Center Miami FL EP172020
300 PM MDT Mon Sep 21 2020
Tropical Depression Seventeen-E has continued to have a ragged
appearance in satellite imagery during the day. The circulation is
elongated, with the main center just northeast of a poorly organized
convective mass and a secondary vorticity maximum well to the
north-northeast near Socorro Island. However, recent scatterometer
data showed an area of 35-40 kt winds to the south and southeast of
the main center. Based on this, the depression is upgraded to
Tropical Storm Lowell with an initial intensity of 40 kt.
The initial motion is now 290/14 kt. There are no significant
changes in the track forecast philosophy, the track forecast
guidance, or the track forecast since the last advisory. Lowell is
being steered by a large low- to mid-level ridge to the north and
northwest, and this ridge is forecast to persist through the
forecast period. The track guidance shows that the system should
continue west-northwestward for about 36 h, followed by a westward
motion through 120 h. The track guidance is still very tightly
clustered, and the new forecast track is near the various consensus
models.
Lowell is still experiencing some easterly shear, which the models
suggest should abate some in the next 12 h or so. However, the
poor organization of the storm suggests it may take a while to
respond to the more favorable environment. Thus, the new intensity
forecast continues the trend of the old forecast in showing slow
strengthening for the first 36-48 h. After that time, the intensity
will be strongly dependent on where the center is in relation to the
strong sea-surface temperature gradient. Since the forecast track
is basically unchanged, the new intensity forecast has only minor
tweaks from the previous forecast based on the forecast track
keeping the system over 25-26C water temperatures through 120 h.
However, any motion north of the forecast track would bring the
center over colder water and lead to a system weaker than forecast,
while any motion south of the track would keep it over warmer water
and possibly allow the cyclone to become a hurricane. The intensity
forecast remains low confidence.
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