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Tropical Storm Irwin Forecast Discussion


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000
WTPZ45 KNHC 262039
TCDEP5

Tropical Storm Irwin Discussion Number  18
NWS National Hurricane Center Miami FL       EP102017
200 PM PDT Wed Jul 26 2017

Irwin is a sheared tropical cyclone with the center exposed and
located on the southern edge of the convection. The shear is
probably caused by the outflow from Hurricane Hilary. An average of
the Dvorak T-numbers and data from a recent scatterometer pass yield
an initial intensity of 45 kt. The shear will likely continue, but
it is not expected to be strong enough to further disrupt the
structure of the cyclone. The NHC forecast calls for no change in
intensity during the next 5 days as per the previous advisory. Most
of the guidance maintains a near-steady intensity.

The cyclone is currently embedded within weak steering currents, and
it is moving toward the west-southwest or 250 degrees at 6 kt. No
change in the steering flow is noted in the global models for the
next day or two, so Irwin will likely continue its current slow
motion. Thereafter, Hurricane Hilary is forecast to pass well north
of Irwin, and the steering currents will change to southerlies. Most
of the models agree that Irwin should begin to move with a northerly
or north-northwesterly component in the wake of Hilary. This is
reflected in the official NHC forecast which, is in the middle of
the guidance envelope.


FORECAST POSITIONS AND MAX WINDS

INIT  26/2100Z 15.1N 122.8W   45 KT  50 MPH
 12H  27/0600Z 14.9N 123.7W   45 KT  50 MPH
 24H  27/1800Z 14.5N 124.7W   45 KT  50 MPH
 36H  28/0600Z 14.5N 125.5W   45 KT  50 MPH
 48H  28/1800Z 14.5N 126.0W   45 KT  50 MPH
 72H  29/1800Z 15.5N 125.0W   45 KT  50 MPH
 96H  30/1800Z 18.0N 126.0W   45 KT  50 MPH
120H  31/1800Z 21.0N 128.5W   45 KT  50 MPH

$$
Forecaster Avila