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Tropical Storm Lowell Discussion Number 11
NWS National Hurricane Center Miami FL EP172020
1100 PM HST Tue Sep 22 2020
Lowell's center is located near the northern edge of a band of deep
convection which extends over the eastern and southern portion of
the circulation due to moderate northwesterly shear in the
mid-levels below the cirrus layer. That part of the circulation
also happens to be where the tropical storm force winds are
predominantly situated, and a recent ASCAT pass showed that the
strongest winds have increased to near 45 kt. Lowell's circulation
will be straddling a tight sea surface temperature gradient during
the next few days, with the center moving over gradually cooler
waters and toward a drier air mass. As a result, little change in
strength is expected during the next couple of days, and some
weakening should begin by day 3 when water temperatures fall below
25 degrees Celsius and moderate westerly or southwesterly shear
sets in. The new NHC intensity forecast is largely an update of
the previous prediction and closely follows the HCCA, Florida State
Superensemble, and IVCN intensity consensus. Lowell is likely to
lose its deep convection and degenerate to a remnant low by day 4.
Lowell has been moving steadily toward the west-northwest, or
295/10 kt, steered by a mid-tropospheric high pressure area
centered just off the west coast of the Baja California peninsula.
The subtropical ridge is expected to become a little more
established to the north of Lowell, and that should cause the storm
to turn westward by 36 hours and continue at that heading through
the end of the forecast period. There continues to be very little
cross-track spread among the track guidance, and the most
noteworthy differences are the forward speeds depicted by the
models, bracketed by the speedy ECMWF and the more sluggish GFS and
COAMPS-TC models. The models overall have continued to trend
faster, and the new NHC track forecast is again pushed ahead of the
previous prediction, lying close to the TVCE consensus and the HCCA
aid.
FORECAST POSITIONS AND MAX WINDS
INIT 23/0900Z 19.8N 119.9W 45 KT 50 MPH
12H 23/1800Z 20.3N 121.3W 45 KT 50 MPH
24H 24/0600Z 20.7N 123.0W 45 KT 50 MPH
36H 24/1800Z 21.0N 124.9W 45 KT 50 MPH
48H 25/0600Z 21.1N 126.9W 45 KT 50 MPH
60H 25/1800Z 21.2N 129.1W 45 KT 50 MPH
72H 26/0600Z 21.2N 131.3W 40 KT 45 MPH
96H 27/0600Z 21.0N 135.7W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 28/0600Z 21.1N 140.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
$$
Forecaster Berg
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