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Hurricane Irwin Forecast Discussion Number 12
2017-07-25 10:58:33| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Tue Jul 25 2017 000 WTPZ45 KNHC 250858 TCDEP5 Hurricane Irwin Discussion Number 12 NWS National Hurricane Center Miami FL EP102017 200 AM PDT Tue Jul 25 2017 Deep convection associated with Irwin now wraps almost all of the way around the center, and there have been occasional hints of a eye in microwave and conventional satellite imagery. Subjective satellite estimates from TAFB and SAB are just below hurricane strength, while several objective estimates, including the CIMSS satellite consensus, are above hurricane strength. With the attempts at eye formation, the initial intensity will lean toward the higher intensity estimates, and thus Irwin is upgraded to a hurricane. The initial motion is a little more northward than before at 300/4. A slow westward motion is forecast today as a weak mid-level ridge remains in place to the north of the storm. A west-southwestward motion is expected between 24-72 h as Hurricane Hilary approaches from the east. After that, Irwin is expected to undergo an binary interaction with Hilary, with the most likely result for Irwin being a generally northward motion around the eastern semicircle of Hilary. The details of this are still uncertain, with the ECMWF and Canadian models merging the two cyclones before 120 h, while the GFS and UKMET keep them separate until after 120 h. The new track forecast is similar to the previous forecast through 72 h. After that, it leans towards the GFS/UKMET in keeping the cyclone separate and accelerating Irwin around the eastern side of Hilary. Little change in strength is likely for the next 24 h. After that, increasing shear associated with the outflow of Hilary is likely to cause Irwin to weaken, although there is considerable spread in the guidance as to how much shear and how much weakening. By the end of the forecast period, cooler water along the forecast track and proximity to Hilary should cause additional weakening. The new forecast track is a slight adjustment of the previous track. An alternative intensity scenario is that Irwin dissipates as it is absorbed by Hilary before 120 h. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 15.5N 118.7W 65 KT 75 MPH 12H 25/1800Z 15.3N 119.4W 65 KT 75 MPH 24H 26/0600Z 15.0N 120.5W 65 KT 75 MPH 36H 26/1800Z 14.6N 121.4W 60 KT 70 MPH 48H 27/0600Z 14.3N 122.2W 55 KT 65 MPH 72H 28/0600Z 14.0N 123.0W 55 KT 65 MPH 96H 29/0600Z 16.0N 122.5W 55 KT 65 MPH 120H 30/0600Z 20.0N 123.0W 50 KT 60 MPH $$ Forecaster Beven
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