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Hurricane Hilda Discussion Number 8
NWS National Hurricane Center Miami FL EP082021
800 AM PDT Sun Aug 01 2021
Hilda is a bit of a mess this morning with an elongated cloud
pattern from southeast to northwest and no signs of an eye in
conventional satellite imagery. However, microwave data near 1155
UTC from GPM still shows a well-defined low-level eye, although the
mid-level structure remains degraded from easterly shear. The
current wind speed is held at 75 kt, with this being an uncertain
estimate due to a large spread in the various intensity techniques.
Hilda is moving west-northwestward at about 7 kt, with microwave
data helping to pinpoint the slower movement. The track forecast is
no piece of cake this morning with some interaction anticipated with
Invest 91E to the east in a day or two. While a mid-level ridge
persists to the northwest of Hilda, the southern periphery of the
ridge weakens due to 91E, causing Hilda to take a northwestward
turn in a couple of days. Hilda then should turn back toward the
west-northwest and west by midweek due to the ridge remaining in
place and 91E weakening. This is a tricky forecast because the
guidance is shifting to the right, which at some point will bring
Hilda over cold waters and closer to 91E, changing which
atmospheric layers will dominate steering the tropical cyclone. In
addition, interactions between two systems this close together
aren't easy to forecast in the best of circumstances, and
the latest guidance isn't in great agreement on the future strength
of 91E either. As a compromise, the NHC track forecast is more
conservative in shifting the track to the northeast than the
guidance (remaining on the westerly side of the track envelope),
then gradually comes close to the previous NHC forecast by the end
of the 5-day period. This forecast is obviously rather uncertain,
and a lot of generally better performing aids are to the northeast
of the latest NHC track.
The hurricane still has some chance to intensify during the next day
or so with moderate easterly shear and good inner-core structure.
Still, it is becoming more likely that Hilda is close to its peak
intensity with no signs of the easterly shear abating until the
hurricane moves over cool waters in a few days. Model guidance
generally is lower than the last cycle, and only a few show
strengthening. I'm going to keep the chance for slight strengthening
in the near term, then show a steady drop in intensity due to
persistent (or stronger) easterly shear and marginal water
temperatures. The new intensity forecast is 5 kt lower than the
last one at 36 hours and beyond and that could still be too high,
especially if the track shifts any farther to the north.
FORECAST POSITIONS AND MAX WINDS
INIT 01/1500Z 14.6N 120.2W 75 KT 85 MPH
12H 02/0000Z 14.9N 121.2W 80 KT 90 MPH
24H 02/1200Z 15.4N 122.4W 80 KT 90 MPH
36H 03/0000Z 16.1N 123.4W 75 KT 85 MPH
48H 03/1200Z 16.9N 124.2W 70 KT 80 MPH
60H 04/0000Z 18.0N 125.5W 60 KT 70 MPH
72H 04/1200Z 19.0N 127.0W 50 KT 60 MPH
96H 05/1200Z 20.2N 131.2W 40 KT 45 MPH
120H 06/1200Z 20.5N 135.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
$$
Forecaster Blake
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