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Hurricane Hilary Discussion Number  26
NWS National Hurricane Center Miami FL       EP092017
200 PM PDT Thu Jul 27 2017

Since the last advisory, the structure of Hilary has changed quite
a bit.  The primary feature is now a long band, extending almost
3/4 of the way around the circulation.  Cloud tops have warmed
during this time and a pronounced dry slot is visible over the
eastern half of the circulation.  Subjective and objective Dvorak
intensity estimates have decreased, so the intensity has been
decreased accordingly, to 65 kt.

The intensity guidance remains divided, with the HWRF and COAMPS-TC
models insisting on reintensification, and SHIPS and LGEM
showing steady state or weakening.  Simulated IR imagery from the
HWRF forecast shows the development of a nearly clear eye in only 12
hours.  Given the current structure of the cyclone, this seems
unlikely.  Therefore, the new official intensity forecast favors the
statistical guidance and is a little above a blend of SHIPS and
LGEM through 36 h.  After that time, decreasing SSTs along the
forecast track should result in steady weakening, ultimately causing
the cyclone to become a remnant low.  Since it is the stronger
system, Hilary is still expected to dominate the interaction with
Irwin, and is now forecast to absorb Irwin in about 96 h, as
depicted by the ECMWF.

1-minute visible imagery from GOES-16 was very helpful in
determining the initial position of of Hilary at 1800 UTC, and the
low-level circulation has at times been visible through the higher
cirrus cover.  The initial motion is a somewhat more certain 290/8
kt.  The extent to which Irwin will affect the track of Hilary still
varies between the global models, with the GFS showing a stronger
Hilary moving farther north, and the UKMET and ECMWF showing a
weaker Hilary pulled farther south.  The official track forecast
still lies between these solutions, but favors the southern
solution since the intensity forecast calls for gradual weakening
throughout the forecast period.

FORECAST POSITIONS AND MAX WINDS

INIT  27/2100Z 17.9N 116.6W   65 KT  75 MPH
 12H  28/0600Z 18.3N 117.9W   65 KT  75 MPH
 24H  28/1800Z 19.1N 119.5W   65 KT  75 MPH
 36H  29/0600Z 19.8N 121.3W   60 KT  70 MPH
 48H  29/1800Z 20.5N 123.5W   60 KT  70 MPH
 72H  30/1800Z 21.4N 128.0W   45 KT  50 MPH
 96H  31/1800Z 22.5N 131.7W   35 KT  40 MPH
120H  01/1800Z 23.7N 134.8W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Zelinsky

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