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Hurricane IRWIN


Hurricane Irwin Discussion Number  16
NWS National Hurricane Center Miami FL       EP102017
200 AM PDT Wed Jul 26 2017

An earlier 0500 UTC METOP-A AMSU image and fortuitous ASCAT
A/B overpasses indicate that Irwin's circulation center is located
near the southern edge of the cloud canopy.  Apparently, the
moderate southeasterly outflow produced by Hurricane Hilary is
affecting Irwin's core structure.  Cloud tops have warmed during
the past several hours and a compromise of the Dvorak subjective
T-numbers from SAB and TAFB support an initial intensity of 70 kt
for this advisory.  The global models as well as the
statistical-dynamical intensity guidance show continued slow
weakening during the next 36 hours while the hurricane remains
within the impinging upper-level outflow of Hilary.  Afterward,
further gradual weakening is forecast as the cyclone traverses
cooler oceanic temperatures and enters a less than favorable
thermodynamic environment.  The official forecast is similar to the
previous package and is based on the IVCN consensus.

The much anticipated turn toward the west-southwest has finally
commenced, and the cyclone motion is estimated to be 255/6 kt.
Some binary interaction with Hilary during the next 48 hours or
so should cause Irwin to stall, and then accelerate cyclonically
around the southeast through northeast periphery of Hilary on days
4 and 5.  Global and ensemble models, however, show a much slower
forward motion beyond 72 hours than what was indicated in the
previous advisory, and adjustments to the 96 and 120 hour forecast
periods have been made accordingly.  The NHC forecast reflects this
significant change in the guidance and is based a blend of the TVCX
and HFIP Corrected Consensus (HCCA) models.

The ASCAT 0502 UTC scatterometer data and the RVCN multi-model
consensus were used for the initial and forecast wind radii.


INIT  26/0900Z 15.7N 121.5W   70 KT  80 MPH
 12H  26/1800Z 15.5N 122.5W   65 KT  75 MPH
 24H  27/0600Z 15.1N 123.7W   60 KT  70 MPH
 36H  27/1800Z 14.8N 124.4W   55 KT  65 MPH
 48H  28/0600Z 14.7N 124.7W   55 KT  65 MPH
 72H  29/0600Z 14.9N 124.5W   55 KT  65 MPH
 96H  30/0600Z 18.0N 124.5W   50 KT  60 MPH
120H  31/0600Z 20.5N 126.0W   45 KT  50 MPH

Forecaster Roberts