ZCZC MIATCDEP5 ALL
TTAA00 KNHC DDHHMM
 
Tropical Storm Irwin Discussion Number   3
NWS National Hurricane Center Miami FL       EP102023
500 AM HST Sun Aug 27 2023
 
The system has become better organized during the past several
hours.  This morning's satellite presentation consists of a primary
curved band wrapping around the south and east semi-circles of the
depression and a recent burst of deep convection near the surface
center.  Subjective and available UW-CIMMS objective satellite
intensity estimates support increasing the initial intensity to 35
kt for this advisory.  Irwin becomes the ninth named tropical
storm of the 2023 eastern Pacific season.
 
Irwin is expected to remain in marginally favorable atmospheric and 
oceanic conditions for another 12 hours, so some slight 
strengthening should occur.  The cyclone will move over gradually 
decreasing SSTs while entering a thermodynamically dry and stable 
surrounding air mass by mid-period.  Based on these negative 
contributing factors, the NHC intensity forecast shows modest 
strengthening in the short term, then slow weakening through 
the remaining portion of the forecast while indicating Irwin as a 
remnant low by day 4.  A compromise of the various consensus 
intensity models was used for the NHC intensity forecast.
 
The initial motion is estimated to be west-northwestward, or
295/10 kt.  The forecast track philosophy remains unchanged for 
this advisory.  A strong subtropical ridge extending westward from 
the southwestern U.S. to the eastern Pacific should steer the 
cyclone in a generally west-northwestward heading through the 24 
hour period.  Afterward, a turn toward the west with an increase in 
forward motion is expected through day 3 as the ridge to the north 
builds westward over the central part of the eastern Pacific.  A 
reduction in forward speed is anticipated for the remaining portion 
of the forecast.  At the same time, Irwin weakens to a vertically 
shallow system and is steered by the low-level tradewind flow.  The 
track forecast lies between the HFIP HCCA consensus model and the 
TVCE simple multi-model aid.  


 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/1500Z 16.8N 120.7W   35 KT  40 MPH
 12H  28/0000Z 17.3N 122.0W   40 KT  45 MPH
 24H  28/1200Z 17.8N 123.9W   40 KT  45 MPH
 36H  29/0000Z 18.2N 126.4W   40 KT  45 MPH
 48H  29/1200Z 18.2N 129.5W   40 KT  45 MPH
 60H  30/0000Z 18.0N 132.6W   35 KT  40 MPH
 72H  30/1200Z 18.0N 135.3W   35 KT  40 MPH
 96H  31/1200Z 18.4N 138.9W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  01/1200Z 18.7N 141.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Roberts
 
NNNN