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Tropical Storm Irwin Forecast Discussion Number 7
2017-07-24 04:32:54| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Sun Jul 23 2017 000 WTPZ45 KNHC 240232 TCDEP5 Tropical Storm Irwin Discussion Number 7 NWS National Hurricane Center Miami FL EP102017 800 PM PDT Sun Jul 23 2017 Irwin is gradually gaining strength. Deep convection has increased over the center during the past several hours, and the cloud pattern now consists of a central dense overcast with fragmented curved bands over the southern portion of the circulation. The Dvorak classifications from TAFB and SAB were both 3.0/45 kt, and the initial wind speed is increased to that value. This intensity estimate is also in agreement with an ASCAT-A pass from around 1800 UTC that showed maximum winds in the 40-45 kt range. Irwin is moving westward at 7 kt to the south of a relatively weak low- to mid-level ridge. This ridge is expected to guide Irwin slowly westward during the next few days. After that time, the forecast track becomes much more uncertain as the path of Irwin depends upon the degree of interaction it has with Hilary to its east. The global models all show Irwin slowing down significantly in a few days and then moving north or northeast as it becomes embedded in the circulation of Hilary. Conversely, the hurricane regional models HWRF, HMON, and COAMPS-TC show Irwin continuing generally westward. The NHC track forecast has been shifted a little to the north and west at days 4 and 5, but continues to lie to the east of the consensus aids favoring the global model solutions. The tropical storm is located in an environment of moderate shear, relatively moist conditions, and over 28 degree C water. These conditions are expected to change little during the next couple of days, and should allow for gradual intensification. Beyond that time, an increase in wind shear associated with the outflow of Hilary would likely cause Irwin to weaken some. The NHC intensity forecast is a little higher than the previous one, trending closer to the latest consensus models HCCA and IVCN. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 14.9N 117.3W 45 KT 50 MPH 12H 24/1200Z 14.8N 118.0W 55 KT 65 MPH 24H 25/0000Z 14.8N 118.8W 60 KT 70 MPH 36H 25/1200Z 14.8N 119.6W 65 KT 75 MPH 48H 26/0000Z 14.7N 120.6W 70 KT 80 MPH 72H 27/0000Z 14.2N 122.8W 65 KT 75 MPH 96H 28/0000Z 14.0N 124.2W 60 KT 70 MPH 120H 29/0000Z 14.5N 124.5W 60 KT 70 MPH $$ Forecaster Cangialosi
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