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