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Hurricane Irwin Forecast Discussion Number 15
2017-07-26 04:57:15| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Tue Jul 25 2017 000 WTPZ45 KNHC 260256 TCDEP5 Hurricane Irwin Discussion Number 15 NWS National Hurricane Center Miami FL EP102017 800 PM PDT Tue Jul 25 2017 Irwin has strengthened a little more during the past several hours. The eye of the hurricane has been occasionally evident in satellite images and cloud tops in the eyewall are quite cold, close to -80 C. The convective structure is asymmetric, however, with the majority of the deepest convection located to the west of the center. The latest Dvorak classifications have increased slightly, and support nudging the initial intensity upward to 80 kt. Irwin is moving westward at 7 kt as it is still being steered by a mid-level ridge to its northeast. A turn to the west-southwest is expected tonight and Wednesday as Hurricane Hilary approaches from the east. The forward motion of Irwin will likely come to a halt on Thursday and Friday as Hilary passes by to the north. After that time, a general northward motion is expected as Irwin gets caught in the flow on the east side of Hilary's circulation. The models are in better agreement compared to previous cycles, but there is still a fair amount of spread in where and when Irwin makes the northward turn. The NHC track forecast is largely an update of the previous one, and lies closest to the multi-model consensus TVCE. The hurricane could be nearing its peak intensity, and weakening should commence soon due to moderate wind shear and the potential for cold water upwelling due to the expected slow motion of Irwin. By the end of the forecast period, Irwin will be moving over much cooler SSTs and into a drier air mass, which should continue the weakening trend. The models are in good agreement, and the NHC intensity forecast lies near the middle of the guidance envelope. Irwin is a very compact hurricane. ASCAT data from around 1800 UTC indicated that the tropical storm force winds extend no more than 60 n mi from the center. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 16.1N 120.9W 80 KT 90 MPH 12H 26/1200Z 15.7N 121.9W 75 KT 85 MPH 24H 27/0000Z 15.2N 123.0W 70 KT 80 MPH 36H 27/1200Z 14.9N 123.8W 60 KT 70 MPH 48H 28/0000Z 14.7N 124.0W 55 KT 65 MPH 72H 29/0000Z 15.5N 123.5W 55 KT 65 MPH 96H 30/0000Z 18.2N 123.5W 55 KT 65 MPH 120H 31/0000Z 22.0N 126.0W 45 KT 50 MPH $$ Forecaster Cangialosi
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