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Hurricane Hilda Forecast Discussion


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000
WTPZ43 KNHC 011450
TCDEP3

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