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Tropical Storm IRWIN Forecast Discussion Number 9
2017-07-24 16:58:55| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Mon Jul 24 2017 000 WTPZ45 KNHC 241458 TCDEP5 Tropical Storm Irwin Discussion Number 9 NWS National Hurricane Center Miami FL EP102017 800 AM PDT Mon Jul 24 2017 Irwin's structure continues to improve, with the low-level center embedded beneath a CDO feature that has persisted for the past several hours. In addition, recent microwave data have revealed the formation of a mid-level eye. Dvorak satellite intensity estimates now range between T3.0/45 kt and T3.5/55 kt, so the initial intensity is raised accordingly to 50 kt. For once, the track forecast for a tropical cyclone is more challenging and more uncertain that its intensity forecast. Irwin is expected to have some binary interaction with Hurricane Hilary beginning in about 3 days, but the amount of interaction is still highly uncertain. The ECMWF, UKMET, and Canadian models all show a strong Fujiwhara interaction, with Irwin swinging to the east and northeast of Hilary by day 5. The GFS shows much less interaction, with Irwin staying well to the southwest of Hilary on day 5, and the regional HWRF and HMON models don't even seem to know about Hilary's existence to allow an interaction to occur. Needless to say, there is significant, higher-than-normal spread in the track guidance beginning in about 72 hours. The updated NHC track forecast continues to show a slow westward motion through day 3, followed by an acceleration toward the northwest and north-northwest on days 4 and 5. At the longer ranges, this forecast is closest to HCCA, but future adjustments are likely due to the significant spread among the models and their ensemble members. Since it appears that Irwin is developing a well-defined inner core, it is likely well on its way to becoming a hurricane. Vertical shear is forecast to be low for the next 48 hours or so, while sea surface temperatures are very warm between 28-29 deg Celsius. The NHC intensity forecast is generally a blend of HCCA and the ICON intensity consensus, bringing Irwin to hurricane status by 24 hours. Significant strengthening beyond that threshold is not anticipated at this time due to the possibility of increased shear from Hilary's outflow, and the NHC forecast shows little change in intensity between days 3 and 5. FORECAST POSITIONS AND MAX WINDS INIT 24/1500Z 14.8N 117.5W 50 KT 60 MPH 12H 25/0000Z 14.8N 117.9W 60 KT 70 MPH 24H 25/1200Z 15.0N 118.6W 70 KT 80 MPH 36H 26/0000Z 15.0N 119.6W 70 KT 80 MPH 48H 26/1200Z 14.9N 120.6W 70 KT 80 MPH 72H 27/1200Z 14.4N 122.2W 65 KT 75 MPH 96H 28/1200Z 15.0N 123.0W 65 KT 75 MPH 120H 29/1200Z 17.0N 124.0W 60 KT 70 MPH $$ Forecaster Berg
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