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Tropical Storm Irwin Discussion Number  25
NWS National Hurricane Center Miami FL       EP102017
800 AM PDT Fri Jul 28 2017

Irwin's structure has not changed significantly during the past
several hours, and deep convection near the center has been
blossoming intermittently.  Dvorak T-numbers have also been
fluctuating, and the best estimate of the initial intensity is 50
kt. SHIPS model data indicate some shear over the cyclone but not
strong enough to disrupt the cloud pattern. On this basis, the NHC
forecast calls for only small fluctuations in intensity during the
next 24 to 36 hours. Thereafter, the circulation is expected to
reach cooler waters and weakening should begin. This process will
continue until Irwin and Hilary merge in about 96 hours or sooner.

Irwin is embedded in light steering currents, and the cyclone has
barely moved during the past few hours. Little motion is
anticipated today or early Saturday, but after that time, Irwin
should be steered northward and northwestward by the southerly
flow in the wake of Hilary. Track guidance is in good agreement
that little motion will occur during the next day or so. There is a
big difference in both direction and speed among models beyond 3
days with the northernmost GFS and the southernmost ECMWF marking
the edges of the broad guidance envelope. However, by then, Irwin
and Hilary should have already merged.


FORECAST POSITIONS AND MAX WINDS

INIT  28/1500Z 14.8N 125.3W   50 KT  60 MPH
 12H  29/0000Z 14.8N 125.3W   55 KT  65 MPH
 24H  29/1200Z 15.2N 125.4W   55 KT  65 MPH
 36H  30/0000Z 16.2N 125.3W   50 KT  60 MPH
 48H  30/1200Z 18.0N 125.5W   45 KT  50 MPH
 72H  31/1200Z 21.5N 128.0W   35 KT  40 MPH
 96H  01/1200Z...Merge with Hilary

$$
Forecaster Avila

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