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Hurricane Linda Discussion Number  25
NWS National Hurricane Center Miami FL       EP122021
1100 PM HST Sun Aug 15 2021
 
Linda's satellite presentation continues to be an excellent example
of an annular hurricane with the classic doughnut shape.  The
cloud pattern consists of a +14C warm eye and a deep convective
inner-core while lacking banding features.  The Annular Hurricane
Index (AHI), which is included in the SHIPS intensity output,
calculated an AHI of 75 out of 100, with and AHI of 100 being best
fit to annular structure.  Although the inner ring's cloud tops
have cooled a bit in the south quadrant (-67C), the northwest
portion of the eyewall has thinned out.  It appears as though 
some dry air is beginning to impinge on this part of the hurricane. 
As a result, the objective and subjective satellite intensity 
estimates have decreased and support lowering the initial intensity 
to 90 kt for this advisory.
 
Through Wednesday morning, only steady weakening is forecast as
Linda remains over marginal (26C) sea surface temperatures and in a
low wind shear environment.  Beyond the 60 hour period, Linda will
move over a steep sea-surface temperature gradient (sub -24C) and
enter a dry more stable marine layer which should cause the 
hurricane to weaken more quickly through day 5.  The NHC intensity
forecast continues to follow the Decay-SHIPS model through 60
hours, then uses a blend of the global models and the IVCN/HCCA
consensus aids which show Linda becoming a post-tropical cyclone 
Friday night.
 
The initial motion estimate is west-southwestward, or 250/9 kt,
There is, once again, little change to the track forecast
philosophy as strengthening mid-tropospheric high pressure over the
northeastern Pacific steers Linda west-southwestward to westward
through the 36 hour period.  Afterward, a turn toward the 
west-northwest is expected as Linda rounds the southwestern 
periphery of the aforementioned ridge.  The NHC forecast follows 
the previous one closely and is in good agreement with the latest 
dynamical model consensus, TVCN.
 
A 0338 and a 0454 UTC METOP-A and B scatterometer pass indicated
that Linda's wind radii had expanded a little in the west
semicircle, and adjustments were made, accordingly.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  16/0900Z 18.2N 122.9W   90 KT 105 MPH
 12H  16/1800Z 17.7N 124.2W   90 KT 105 MPH
 24H  17/0600Z 17.5N 125.8W   85 KT 100 MPH
 36H  17/1800Z 17.7N 127.6W   80 KT  90 MPH
 48H  18/0600Z 18.2N 129.8W   75 KT  85 MPH
 60H  18/1800Z 19.0N 132.1W   65 KT  75 MPH
 72H  19/0600Z 19.9N 134.7W   60 KT  70 MPH
 96H  20/0600Z 21.5N 140.0W   50 KT  60 MPH
120H  21/0600Z 22.6N 145.0W   40 KT  45 MPH...POST-TROPICAL
 
$$
Forecaster Roberts
 
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