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Tropical Storm Blanca Discussion Number 5
NWS National Hurricane Center Miami FL EP022021
300 PM MDT Mon May 31 2021
Thunderstorms activity has increased markedly since the previous
advisory and convection now wraps almost 75 percent around the
well-defined low-level center. A bullseye ASCAT-B and a partial
ASCAT-A pass at 1717Z and 1602Z, respectively, depicted a few
35-kt surface vectors just northwest of the tight low-level center
along with a small radius of maximum winds (RMW) of about 15 nmi.
Based on the continued increase in the convective organization since
the ASCAT passes, the advisory intensity has been raised to 40 kt,
which is a little below the consensus T3.0/45 kt satellite
intensity classifications from TAFB and SAB, and objective intensity
estimates of 46 kt and 47 kt from UW-CIMSS ADT and SATCON,
respectively.
Blanca is forecast to maintain a general west-northwestward to
northwestward motion along the south side of a deep-layer
subtropical ridge for the next 3 days or so. Thereafter, a gradual
turn to the west-northwest is expected on day 4, followed by a
westward motion on day 5 as the cyclone moves over cooler water and
weakens, thus becoming more vertically shallow and steered by the
low-level easterly trade wind flow. The new official NHC forecast
track is similar to the previous advisory track and lies near the
center of the tightly packed guidance envelope, which is close to
an average of the consensus track models TVCE and HCCA.
Blanca is expected to remain in favorable environmental conditions
of low vertical wind shear less than 10 kt, high oceanic heat
content, and moist low- to mid-level air for the next 24 hours or
so. As a result, steady strengthening is forecast during that
time, with a brief period of rapid intensification a distinct
possibility owing to the cyclone's small RMW. Thereafter, the
combination of increasing westerly wind shear, along with
decreasing SSTs and mid-level humidity, should cause gradual
weakening. The new NHC intensity forecast is a blend of the HWRF,
HCCA, and Decay-SHIPS (DSHP) models, which is slightly above the
previous intensity forecast for the first 24 hours, and then is
very similar to the previous advisory thereafter.
FORECAST POSITIONS AND MAX WINDS
INIT 31/2100Z 13.5N 108.9W 40 KT 45 MPH
12H 01/0600Z 14.0N 109.9W 50 KT 60 MPH
24H 01/1800Z 14.6N 111.0W 55 KT 65 MPH
36H 02/0600Z 15.2N 112.1W 45 KT 50 MPH
48H 02/1800Z 15.6N 113.0W 40 KT 45 MPH
60H 03/0600Z 15.9N 113.7W 35 KT 40 MPH
72H 03/1800Z 16.0N 114.4W 35 KT 40 MPH
96H 04/1800Z 16.2N 116.2W 30 KT 35 MPH
120H 05/1800Z 16.2N 118.1W 25 KT 30 MPH
$$
Forecaster Stewart
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