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Tropical Storm IRWIN


Tropical Storm Irwin Discussion Number  35
NWS National Hurricane Center Miami FL       EP102017
800 PM PDT Sun Jul 30 2017

Irwin is one resilient tropical storm.  Amazingly, the cloud
pattern has improved during the past few hours, with deep
convection forming and rotating around the center even though the
cyclone is now over sea surface temperatures colder than 25 deg C.
A 0002 UTC SSMIS microwave pass revealed a small ring of deep
convection that was partially open on the east side, but it also
suggested that the vortex is tilted a bit with height.  Since Dvorak
estimates from TAFB and SAB are a consensus T3.5, the initial
intensity remains 55 kt.

Irwin will be moving from 24-25C waters to 22-23C waters during the
next 24 hours, so weakening should begin soon.  In fact, it will be
quite difficult for Irwin to continue producing organized deep
convection in about 36 hours, and that is when the NHC forecast
calls for it to degenerate into a remnant low.  Based on global
model fields, the remnant low is forecast to dissipate by day 4, if
not sooner.  No changes to the previous NHC forecast were required
based on the latest intensity guidance.

The forward motion continues to increase as Irwin trails behind
Hilary, and the current estimate is 335/11 kt.  A little more
acceleration toward the north-northwest is expected during the next
12-24 hours, but Irwin should turn northwest and slow down on days
2 and 3 as it moves around the remnant circulation of Hilary.  The
updated NHC track forecast was nudged northeast of the previous
forecast after 24 hours to be closer in line with the latest HCCA
and TVCN guidance, but otherwise no significant changes were needed.


INIT  31/0300Z 19.8N 126.2W   55 KT  65 MPH
 12H  31/1200Z 21.5N 127.1W   50 KT  60 MPH
 24H  01/0000Z 23.9N 128.2W   40 KT  45 MPH
 36H  01/1200Z 26.0N 129.6W   30 KT  35 MPH...POST-TROP/REMNT LOW
 48H  02/0000Z 27.6N 131.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  03/0000Z 28.9N 133.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  04/0000Z...DISSIPATED

Forecaster Berg