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Tropical Storm Irwin Forecast Discussion Number 5
2017-07-23 16:56:47| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Sun Jul 23 2017 000 WTPZ45 KNHC 231456 TCDEP5 Tropical Storm Irwin Discussion Number 5 NWS National Hurricane Center Miami FL EP102017 800 AM PDT Sun Jul 23 2017 Irwin's center is exposed to the north and west of its associated deep convection due to about 15 kt of northerly shear. Subjective and objective Dvorak intensity estimates are a consensus T2.5, so 35 kt will remain the initial intensity for this advisory. The initial motion remains westward at 280/6 kt, with Irwin located south of a weak low-level ridge and almost midway between Tropical Storms Greg and Hilary. This orientation should cause Irwin to maintain a westward, albeit much slower, motion during the next several days. However, once Greg degenerates into a remnant low in about 4 days, a binary interaction between a stronger Irwin and Hilary is more likely to occur, which could force Irwin to turn west-southwestward at the end of the forecast period. There is some notable spread in the guidance, highlighted by the GFS and its ensemble mean on the southern end of the guidance envelope, and the ECMWF and its ensemble mean on the northern edge. The HWRF is also north of most models by the end of the forecast period, presumably because it is not capturing any interaction between Irwin and Hilary. The updated NHC forecast is nudged a little south on this advisory, and it is south of the model consensus after day 3 to account for an Irwin-Hilary track interaction. The shear over Irwin is expected to decrease within the next 12-24 hours, which should allow the cyclone to begin a sustained period of strengthening. Sea surface temperatures will be between 27-28 degrees Celsius, and the ambient environment appears sufficiently moist to foster intensification. The NHC intensity forecast favors a blend of the ICON intensity consensus, HCCA, and the Florida State Superensemble, showing Irwin reaching hurricane intensity in about 48 hours. This forecast is not too different from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 23/1500Z 15.0N 115.8W 35 KT 40 MPH 12H 24/0000Z 15.0N 116.6W 40 KT 45 MPH 24H 24/1200Z 15.0N 117.5W 50 KT 60 MPH 36H 25/0000Z 15.0N 118.2W 60 KT 70 MPH 48H 25/1200Z 15.0N 119.1W 65 KT 75 MPH 72H 26/1200Z 14.8N 121.4W 65 KT 75 MPH 96H 27/1200Z 14.2N 123.9W 60 KT 70 MPH 120H 28/1200Z 14.0N 125.4W 55 KT 65 MPH $$ Forecaster Berg
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