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Tropical Storm Irwin Discussion Number  33
NWS National Hurricane Center Miami FL       EP102017
800 AM PDT Sun Jul 30 2017

Even though Irwin is crossing the 26 deg C isotherm, it does not
appear to be weakening yet.  In fact, recent microwave data indicate
the tropical storm has a mid-level eye, which has occasionally
appeared in geostationary satellite images.  The system is still
producing a fair amount of deep convection, especially to the south
of the center.  The latest Dvorak CI-numbers from TAFB and SAB are
3.5/55 kt and accordingly, the initial intensity is set a bit higher
to 55 kt.  This wind speed estimate is also in agreement with ASCAT
data from several hours ago that showed maximum winds near 50 kt.

Despite the recent increase in intensity, Irwin is expected to begin
weakening soon as it moves over even cooler waters and into a drier
and more stable air mass.  The storm is likely to become a remnant
low in 36 to 48 hours when it will be over SSTs near 22 deg C.  Most
of the global models show the remnant low dissipating in 4 to 5
days.  The NHC intensity forecast follows the trend of the guidance,
and it is largely unchanged from the previous prediction.

Irwin is moving north-northwestward, or 345 degrees, at 8 kt.  The
system is embedded in south-southeasterly flow in the wake of
Hilary, and it is expected to remain in this steering flow for
another day or two.  Once Irwin becomes a remnant low, the shallow
system is expected to turn a little to the left and slow down as it
becomes steered by the low-level flow.  The NHC track forecast is
adjusted a little to the north and east of the previous one, to come
into better agreement with the latest consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  30/1500Z 17.9N 125.4W   55 KT  65 MPH
 12H  31/0000Z 19.4N 126.1W   50 KT  60 MPH
 24H  31/1200Z 21.7N 127.3W   40 KT  45 MPH
 36H  01/0000Z 23.9N 128.6W   35 KT  40 MPH
 48H  01/1200Z 25.7N 130.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  02/1200Z 27.9N 132.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  03/1200Z 29.0N 133.2W   15 KT  15 MPH...POST-TROP/REMNT LOW
120H  04/1200Z...DISSIPATED

$$
Forecaster Cangialosi

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